Karst of East Herzegovina and Dubrovnik Littoral 3031281195, 9783031281198

Table of contents :
Foreword
Preface
Contents
About the Author
1: Natural Characteristics
1.1 Geographical Position
1.2 History of Studies
1.3 Basic Climatological Data
1.3.1 Precipitation
1.3.2 Air Temperatures
1.3.3 Relative Humidity and Evaporation
1.3.4 Hydrological Characteristics
1.4 Geological Characteristics
1.4.1 Lithostratigraphic Characteristics
1.4.2 Regional Forms of Tectonic Composition
1.4.3 Seismicity
1.4.4 Hydrogeological Aspects of Neotectonic Activities
1.4.5 General Hydrogeological Characteristics
1.5 Geomorphological Characteristics
1.5.1 Dry Valleys
1.5.2 Karst Plain
1.5.3 Sinkholes
1.5.4 More Significant Mountains
1.6 Karst Poljes
1.6.1 Popovo Polje
1.6.2 Trebinjsko Polje
1.6.3 Mokro and Petrovo (Dzivarsko) Polje
1.6.4 Bilećko Polje
1.6.5 Ljubomirsko Polje
1.6.6 Ljubinjsko Polje
1.6.7 Fatničko Polje
1.6.8 Dabarsko Polje
1.6.9 Cerničko Polje
1.6.10 Gatačko Polje
1.6.11 Nevesinjsko Polje
1.6.12 Lukavačko Polje
1.6.13 Slato Polje
1.6.14 Trusinsko Polje
1.6.15 Konavosko Polje (Konavli)
1.6.16 Gradac Polje
1.7 Hutovo Blato
References
2: Catchments, Surface Flows, Springs
2.1 Water Catchments and River Flows of East Herzegovina
2.1.1 General Characteristics
2.1.2 Regional Trebisnjica Water Catchment
2.1.3 Catchment Area of Trebisnjica Springs
2.1.4 Musnica River with Gračanica Tributary
2.1.5 Trebisnjica Springs: General Data
2.1.6 Reconstruction of Trebisnjica Karst Aquifer Evolution Process
2.1.7 Hydrogeological Characteristics of Trebisnjica Spring Aquifer
2.1.8 Catchment Areas Between Trebisnjica Spring Zones and Grančarevo
2.1.9 Sub-catchments and Springs Between Grančarevo and Gorica
2.1.10 Catchment Areas of Trebinjsko, Popovo and Mokro Polje
2.1.11 Characteristics of Trebisnjica River Through the Popovo Polje
2.1.12 Zalomka River Catchment Area
2.1.13 Catchment Area of Northern Part of Nevesinjsko Polje
2.1.14 Catchment Area Between Nevesinjsko Polje and Buna-Bunica Springs
2.1.15 Characteristics of Zalomka River
2.1.16 Investigations Along the Zalomka River
2.1.17 Drezanjka Creek and Zovidolka River
2.1.18 Zovidolka Spring: Jama
2.1.19 Jedres and Jezdus Springs
2.1.20 Bregava River
2.1.21 Krupa River
2.2 Springs of Dubrovnik Littoral and Neretva Valley
2.2.1 Springs Along the Adriatic Coast
2.2.2 Ombla: Komolac (Source of Dubrovnik River)
2.2.3 Palace Spring: Mali Zaton
2.2.4 Zavrelje Zavrelje Spring: Mlini
2.2.5 Duboka Ljuta: Robinson Spring
2.2.6 Konavoska Ljuta
2.2.7 The Other Springs of Dubrovnik Littoral
2.3 Springs Along the East Rim of Neretva Valley
2.3.1 Springs Between Kuti and Dračevo
2.3.2 Springs of Hutovo Blato
2.3.3 Buna and Bunica Springs
2.4 Characteristics of Large Ponors and Ponor Zones
References
3: Underground Morphology and Fauna
3.1 Speleology Facilities
3.1.1 Short History of Investigations
3.1.2 Miruse Area (Bileća Reservoir)
3.1.3 Area Trebinje, Zupci and Bijela Gora
3.1.4 Speleological Facilities in Popovo Polje
Ponors Downstream from Velja Meda
3.1.5 Caves Between Popovo Polje and Dubrovnik Littoral
3.1.6 Speleological Facilities in Fatničko and Dabarsko poljes
3.1.7 Speleological Facilities in the Area of Bileća, Korita and Cerničko Polje
3.1.8 Speleological Facilities in the Gatačko Polje Area
3.1.9 Speleological Facilities Nevesinjsko Polje
3.1.10 Polje Gradac-Gradnica Shaft
3.2 Caves-Archaeologic Allocations
3.3 Caves and Shafts for Water Supply
3.4 Fauna
References
4: Water Resources Projects
4.1 Introduction
4.2 Multipurpose Hydrosystem Trebisnjica (HET): Conception
4.3 Reorganization the River Networks in Gatačko Polje
4.4 Dams and Reservoirs
4.4.1 Dam Klinje
4.4.2 Vrba Dam
4.4.3 Gorica Dam and Reservoir
4.4.4 Grančarevo Dam and Bileća Reservoir
Grančarevo Dam
Bileća Reservoir
4.4.5 Upper Regulatory Pool Hutovo (Hutovo Reservoir)
4.4.6 Lower Regulation Pool Svitava
4.4.7 Dam and Alagovac Reservoir
4.4.8 Bukov Creek: Potential Reservoir
4.5 Tunnels
4.5.1 Tunnel for Konavosko Polje Drainage
4.5.2 Access Tunnel for HPP Dubrovnik and Tail Race Tunnel II
4.5.3 Gorica - Plat Tunnel (Head Race Tunnel for HPP Dubrovnik)
4.5.4 Fatnica - Bileća Tunnel
4.5.5 Dabar - Fatnica Tunnel
4.5.6 Tunnel for RPP Čapljina
4.5.7 Tail Race Tunnel of RPP Čapljina
4.5.8 Burst of Underground Water during Excavation of Power Plant Hall of RPP Čapljina
4.5.9 Investigation Adit for HPP Dabar
4.5.10 Lazarići Tunnel
4.5.11 Head Race Tunnel for HPP Dabar
4.6 Remediation of Trebisnjica Riverbed
4.7 Drainage of Mokro and Petrovo Polje
4.8 Plugging Karst Springs
4.8.1 Plugging of Obod Spring in Fatničko Polje
4.8.2 Plugging of Jedres Spring in Nevesinjsko Polje
4.9 Underground Dam and Ombla Reservoir
4.9.1 Development of an Idea
4.9.2 Conception of Underground Dam and Reservoir
4.10 Tapped Springs, Local Water Supply Systems and Irrigation
4.10.1 Oko Spring (Eye Spring): Water Supply for Trebinje
4.10.2 Vratlo Spring (Gračanica River): Gacko Water Supply
4.10.3 Water Intake for Ljubinje
4.10.4 Tappng Structure Palata Mali Zaton
4.11 Tapping Structures and Water Supply Structures as Part of HET Activity
4.11.1 Vrijeka Spring
4.11.2 Jama: Udbine Spring
4.11.3 Irrigation of Trebinjsko and Mokro Polje and Zupci Plateau
4.11.4 Irrigation of Ljubomirsko Polje
4.11.5 Water Intakes along the Trebisnjica Canal
References
5: Influence and Consequences of Water Resources Projects
5.1 Introduction
5.2 Submerging of Living Space, Agricultural Land, Archaeological Sites and Infrastructure
5.3 Reservoirs and Permanent Surface Flows
5.4 Increasing the Minimum Flow through the Town of Stolac
5.5 Natural and Induced Collapses
5.6 Consequences of Water Regime Change
5.6.1 Impoverishment of Karst Aquifers
5.6.2 Influence on Downstream Springs and Submarine Springs
5.6.3 Consequences of Trebisnjica Spring Submergence
5.6.4 Characteristic Floods of Bilećko and Popov Poljes after 1968
5.6.5 The Role of the Hydrosystem on Flood Mitigation
5.6.6 Estimation of Consequences of Partial Water Transfer from Catchments of Buna, Bunica and Bregava into Trebisnjica Catchm...
5.7 Endemic Species Survival
5.8 Induced Seismicity
5.9 Eolian Erosion
5.10 Importance of Water Potential of Southeast Dinarides
References
6: Chemistry and Water Quality
6.1 Water Quality
6.1.1 History of Water Protection and Quality Control
6.1.2 Results of Water Quality Analysis
6.1.3 Turbidity
6.1.4 Self-Purification Capabilities of Karst Underground Flows
6.2 Water Protection
References

Citation preview

Cave and Karst Systems of the World

Petar Milanović

Karst of East Herzegovina and Dubrovnik Littoral

Cave and Karst Systems of the World Series Editor James W. LaMoreaux, P. E. LaMoreaux and Associates, Tuscaloosa, AL, USA

This book series furthers the understanding of cave and karst related processes and facilitates the translation of current discipline-specific research to an interdisciplinary readership by dealing with specific cave or karst systems. Books in this series focus on a specific cave or karst system, on the cave or karst systems of a specific region, on a specific type of cave or karst system, or on any other perspective related to cave and karst systems of the world. The book series addresses a multidisciplinary audience involved in anthropology, archaeology, biology, chemistry, geography, geology, geomorphology, hydrogeology, paleontology, sedimentology, and all other disciplines related to speleology and karst terrains.

Petar Milanović

Karst of East Herzegovina and Dubrovnik Littoral

Petar Milanović BELGRADE, Serbia

ISSN 2364-4591 ISSN 2364-4605 (electronic) Cave and Karst Systems of the World ISBN 978-3-031-28119-8 ISBN 978-3-031-28120-4 (eBook) https://doi.org/10.1007/978-3-031-28120-4 # The Editor(s) (if applicable) and The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 This work is subject to copyright. All rights are solely and exclusively licensed by the Publisher, whether the whole or part of the material is concerned, specifically the rights of translation, reprinting, reuse of illustrations, recitation, broadcasting, reproduction on microfilms or in any other physical way, and transmission or information storage and retrieval, electronic adaptation, computer software, or by similar or dissimilar methodology now known or hereafter developed. The use of general descriptive names, registered names, trademarks, service marks, etc. in this publication does not imply, even in the absence of a specific statement, that such names are exempt from the relevant protective laws and regulations and therefore free for general use. The publisher, the authors, and the editors are safe to assume that the advice and information in this book are believed to be true and accurate at the date of publication. Neither the publisher nor the authors or the editors give a warranty, expressed or implied, with respect to the material contained herein or for any errors or omissions that may have been made. The publisher remains neutral with regard to jurisdictional claims in published maps and institutional affiliations. This Springer imprint is published by the registered company Springer Nature Switzerland AG The registered company address is: Gewerbestrasse 11, 6330 Cham, Switzerland

Foreword

This new volume in Springer’s Advances in Karst Science Book Series builds upon the existing studies and literature and documents the historic and diverse zone of karst features in Central Europe. It presents a fresh and detailed look at both the past and current research and explores the unique and complex geology of a special geographic zone. Due to the sensitive nature of this special karst environment, future growth and development must be planned and implemented very carefully. With the diversity and delicate nature of its resources, the Dinaric Karst makes up many significant cavern systems, supports specialized agriculture, and is home to a population who copes annually with the reoccurring cycles of flood and drought due to the area’s unique geology. Petar has worked as a Senior Associate of PE LaMoreaux & Associates (www.pela.com) and he and his family and our family share many experiences in working together professionally and personally. It is my honor to write the Foreword for this fine addition to Springer’s (www.springer.com) series. I also had the opportunity to tour the area firsthand with Petar as one of the field trip leaders during the Karst Symposium: Expect the Unexpected in Trebinje, Bosnia-Herzegovina pre pandemic. Petar and his son Sasa and I and my father Dr. Phil LaMoreaux have served as members of the International Association of Hydrogeologists (IAH) Karst Commission. The Commission has been and continues to be a catalyst for much of the research and many of the publications in this series and in the Cave and Karst Systems of the World Book Series of which I am Editor. It is my pleasure, therefore, to introduce this work to you the reader. May you find it both enjoyable and helpful. P. E. LaMoreaux and Associates Tuscaloosa, AL, USA

James W. LaMoreaux

v

Preface

From 1968 to the present day, my key professional preoccupation has been karst and, above all, the engineering problems of karst—engineering karstology. From 1968 to 1988, I lived and worked in Trebinje in East Herzegovina, in an area with the most challenging karst according to Cvijić, “the most complete karst.” Even after 1988, my professional interest and continuous presence in the karst area of East Herzegovina and the Dubrovnik coast did not stop. That period, more than half a century, is characterized by the construction of one of the world’s most complex water management systems that needs to be built and survive in a natural environment that does not tolerate changes. It is a multi-purpose system of hydroelectric power plants on the Trebišnjica River. Its basic purpose is to master the extremely unfavorable regime of the most important natural resource, water, to the development of the region, but at the same time, to protect essential values of its natural and ethno characteristics. Previous world experience gained from the construction of similar facilities in karst warned of numerous problems and even failures. It was clearly indicated that the basic condition for implementation of such a complex regional project is detailed knowledge of the specific nature of the karst of East Herzegovina, where underground flow dominates, and the water regime is characterized by alternating floods and droughts. In order to reduce the ever-present risk of construction in karst to a minimum and to assess possible unwanted consequences in advance, extensive multidisciplinary research was carried out. Those works were started more than 60 years ago and continue, with greater or lesser intensity, until today. Numerous facilities have been successfully built, some of which have been in operation for more than 50 years. In the form of project documentation and numerous professional works, a great deal of experience has been accumulated, which is interesting for researchers and builders in karst regions. Fifteen years ago, I presented part of this experience and numerous exact data on which it is based, in the form of a monograph entitled “Karst of East Herzegovina and the Dubrovnik Littoral” (in Serbian). From then until today, the construction of the Trebišnjica Hydrosystem has continued, primarily in the area known as Upper Horizons. Since it is a technologically integral hydrosystem, with the objective of complex regulation of the water regime, including the partial transfer of water from the Neretva basin to the Trebišnjica basin, extensive analyses were carried out with the aim of improving the existing concept. There were also extreme natural phenomena (rainfall and floods) that affected the operation of the already built part of the system. Numerous research works were also carried out, with the aim of getting to know the nature of the karst in the areas that should be functionally integrated into the system. Great attention was focused on the water supply and irrigation of parts of East Herzegovina, with the age-old problem of water shortage. Many new investigative works were carried out, a large amount of new information was collected, and new facilities were built. Due to all of the above, I believe there is a need for a new significantly supplemented edition, in which the data of new research, observations, and knowledge about karst are updated. I have the great honor and pleasure of thanking the reviewers, world-recognized authorities on hydrogeology and karst hydrology: Prof. Zoran Stevanović, University of Belgrade, and Prof. Ognjen Bonacci, Civil Engineering Facility of Split, as well as Duško Vujović, B.Sc. civil vii

viii

Preface

engineer, great enthusiast, and exceptional connoisseur of the issues presented in the text. They all contributed significantly to the quality of the book with their suggestions and additional information. I wish to express my deep appreciation to Dr. James LaMoreaux, Series Editor of Advance in Karst Science, for his support and inspiration to publish this book. In particular, I would like to thank my daughter Prof. Tina Dašić, graduate civil engineer, for numerous suggestions and great effort in the final preparation of the book. BELGRADE, Serbia

Petar Milanović

Contents

1

Natural Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1 1.1 Geographical Position . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.2 History of Studies . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.3 Basic Climatological Data . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 1.3.1 Precipitation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.3.2 Air Temperatures . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.3.3 Relative Humidity and Evaporation . . . . . . . . . . . . . . . . . . . . . . . . 9 1.3.4 Hydrological Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.4 Geological Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.4.1 Lithostratigraphic Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.4.2 Regional Forms of Tectonic Composition . . . . . . . . . . . . . . . . . . . 16 1.4.3 Seismicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 17 1.4.4 Hydrogeological Aspects of Neotectonic Activities . . . . . . . . . . . . 18 1.4.5 General Hydrogeological Characteristics . . . . . . . . . . . . . . . . . . . . 19 1.5 Geomorphological Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 1.5.1 Dry Valleys . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 30 1.5.2 Karst Plain . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 31 1.5.3 Sinkholes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 1.5.4 More Significant Mountains . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 33 1.6 Karst Poljes . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 1.6.1 Popovo Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 38 1.6.2 Trebinjsko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 52 1.6.3 Mokro and Petrovo (Dživarsko) Polje . . . . . . . . . . . . . . . . . . . . . . 54 1.6.4 Bilećko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 1.6.5 Ljubomirsko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 1.6.6 Ljubinjsko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 60 1.6.7 Fatničko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 62 1.6.8 Dabarsko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 69 1.6.9 Cerničko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 71 1.6.10 Gatačko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 76 1.6.11 Nevesinjsko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 81 1.6.12 Lukavačko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 87 1.6.13 Slato Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 89 1.6.14 Trusinsko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 90 1.6.15 Konavosko Polje (Konavli) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 1.6.16 Gradac Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 1.7 Hutovo Blato . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 92 References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 106

2

Catchments, Surface Flows, Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 109 2.1 Water Catchments and River Flows of East Herzegovina . . . . . . . . . . . . . . . 110 2.1.1 General Characteristics . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 110 ix

x

Contents

2.1.2 2.1.3 2.1.4 2.1.5 2.1.6 2.1.7 2.1.8

Regional Trebišnjica Water Catchment . . . . . . . . . . . . . . . . . . . . . Catchment Area of Trebišnjica Springs . . . . . . . . . . . . . . . . . . . . . Mušnica River with Gračanica Tributary . . . . . . . . . . . . . . . . . . . . Trebišnjica Springs: General Data . . . . . . . . . . . . . . . . . . . . . . . . . Reconstruction of Trebišnjica Karst Aquifer Evolution Process . . . . Hydrogeological Characteristics of Trebišnjica Spring Aquifer . . . . Catchment Areas Between Trebišnjica Spring Zones and Grančarevo . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.9 Sub-catchments and Springs Between Grančarevo and Gorica . . . . . 2.1.10 Catchment Areas of Trebinjsko, Popovo and Mokro Polje . . . . . . . 2.1.11 Characteristics of Trebišnjica River Through the Popovo Polje . . . . 2.1.12 Zalomka River Catchment Area . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.13 Catchment Area of Northern Part of Nevesinjsko Polje . . . . . . . . . . 2.1.14 Catchment Area Between Nevesinjsko Polje and Buna-Bunica Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.15 Characteristics of Zalomka River . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.16 Investigations Along the Zalomka River . . . . . . . . . . . . . . . . . . . . 2.1.17 Drežanjka Creek and Zovidolka River . . . . . . . . . . . . . . . . . . . . . . 2.1.18 Zovidolka Spring: Jama . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.19 Jedreš and Jezduš Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.20 Bregava River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.1.21 Krupa River . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2 Springs of Dubrovnik Littoral and Neretva Valley . . . . . . . . . . . . . . . . . . . 2.2.1 Springs Along the Adriatic Coast . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.2 Ombla: Komolac (Source of Dubrovnik River) . . . . . . . . . . . . . . . 2.2.3 Palace Spring: Mali Zaton . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.4 Zavrelje Zavrelje Spring: Mlini . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.5 Duboka Ljuta: Robinson Spring . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.6 Konavoska Ljuta . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.2.7 The Other Springs of Dubrovnik Littoral . . . . . . . . . . . . . . . . . . . . 2.3 Springs Along the East Rim of Neretva Valley . . . . . . . . . . . . . . . . . . . . . . 2.3.1 Springs Between Kuti and Dračevo . . . . . . . . . . . . . . . . . . . . . . . . 2.3.2 Springs of Hutovo Blato . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.3.3 Buna and Bunica Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2.4 Characteristics of Large Ponors and Ponor Zones . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

Underground Morphology and Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1 Speleology Facilities . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.1 Short History of Investigations . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.2 Miruše Area (Bileća Reservoir) . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.3 Area Trebinje, Zupci and Bijela Gora . . . . . . . . . . . . . . . . . . . . . . 3.1.4 Speleological Facilities in Popovo Polje . . . . . . . . . . . . . . . . . . . . 3.1.5 Caves Between Popovo Polje and Dubrovnik Littoral . . . . . . . . . . . 3.1.6 Speleological Facilities in Fatničko and Dabarsko poljes . . . . . . . . 3.1.7 Speleological Facilities in the Area of Bileća, Korita and Cerničko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.1.8 Speleological Facilities in the Gatačko Polje Area . . . . . . . . . . . . . 3.1.9 Speleological Facilities Nevesinjsko Polje . . . . . . . . . . . . . . . . . . . 3.1.10 Polje Gradac–Gradnica Shaft . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.2 Caves-Archaeologic Allocations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.3 Caves and Shafts for Water Supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3.4 Fauna . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

111 111 113 114 115 117 119 121 123 126 129 130 131 131 133 139 140 140 141 146 146 146 147 152 155 157 159 159 162 163 164 166 167 170 173 174 174 176 176 177 179 183 185 185 186 188 189 190 191 193

Contents

xi

4

5

Water Resources Projects . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.2 Multipurpose Hydrosystem Trebišnjica (HET): Conception . . . . . . . . . . . . . 4.3 Reorganization the River Networks in Gatačko Polje . . . . . . . . . . . . . . . . . 4.4 Dams and Reservoirs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.1 Dam Klinje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.2 Vrba Dam . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.3 Gorica Dam and Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.4 Grančarevo Dam and Bileća Reservoir . . . . . . . . . . . . . . . . . . . . . 4.4.5 Upper Regulatory Pool Hutovo (Hutovo Reservoir) . . . . . . . . . . . . 4.4.6 Lower Regulation Pool Svitava . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.7 Dam and Alagovac Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.4.8 Bukov Creek: Potential Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . 4.5 Tunnels . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.1 Tunnel for Konavosko Polje Drainage . . . . . . . . . . . . . . . . . . . . . . 4.5.2 Access Tunnel for HPP Dubrovnik and Tail Race Tunnel II . . . . . . 4.5.3 Gorica - Plat Tunnel (Head Race Tunnel for HPP Dubrovnik) . . . . . 4.5.4 Fatnica - Bileća Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.5 Dabar - Fatnica Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.6 Tunnel for RPP Čapljina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.7 Tail Race Tunnel of RPP Čapljina . . . . . . . . . . . . . . . . . . . . . . . . 4.5.8 Burst of Underground Water during Excavation of Power Plant Hall of RPP Čapljina . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.9 Investigation Adit for HPP Dabar . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.10 Lazarići Tunnel . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.5.11 Head Race Tunnel for HPP Dabar . . . . . . . . . . . . . . . . . . . . . . . . . 4.6 Remediation of Trebišnjica Riverbed . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.7 Drainage of Mokro and Petrovo Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8 Plugging Karst Springs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.8.1 Plugging of Obod Spring in Fatničko Polje . . . . . . . . . . . . . . . . . . 4.8.2 Plugging of Jedreš Spring in Nevesinjsko Polje . . . . . . . . . . . . . . . 4.9 Underground Dam and Ombla Reservoir . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.1 Development of an Idea . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.9.2 Conception of Underground Dam and Reservoir . . . . . . . . . . . . . . 4.10 Tapped Springs, Local Water Supply Systems and Irrigation . . . . . . . . . . . . 4.10.1 Oko Spring (Eye Spring): Water Supply for Trebinje . . . . . . . . . . . 4.10.2 Vratlo Spring (Gračanica River): Gacko Water Supply . . . . . . . . . . 4.10.3 Water Intake for Ljubinje . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.10.4 Tappng Structure Palata Mali Zaton . . . . . . . . . . . . . . . . . . . . . . . 4.11 Tapping Structures and Water Supply Structures as Part of HET Activity . . . 4.11.1 Vrijeka Spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11.2 Jama: Udbine Spring . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11.3 Irrigation of Trebinjsko and Mokro Polje and Zupci Plateau . . . . . . 4.11.4 Irrigation of Ljubomirsko Polje . . . . . . . . . . . . . . . . . . . . . . . . . . . 4.11.5 Water Intakes along the Trebišnjica Canal . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

195 196 198 204 205 205 208 208 214 220 229 230 230 231 234 234 235 240 246 248 252

Influence and Consequences of Water Resources Projects . . . . . . . . . . . . . . . . 5.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.2 Submerging of Living Space, Agricultural Land, Archaeological Sites and Infrastructure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.3 Reservoirs and Permanent Surface Flows . . . . . . . . . . . . . . . . . . . . . . . . . . 5.4 Increasing the Minimum Flow through the Town of Stolac . . . . . . . . . . . . .

287 288

254 254 254 255 256 259 260 260 262 264 264 271 274 278 278 278 278 280 280 280 282 282 283 285

288 290 291

xii

Contents

5.5 5.6

6

Natural and Induced Collapses . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Consequences of Water Regime Change . . . . . . . . . . . . . . . . . . . . . . . . . . 5.6.1 Impoverishment of Karst Aquifers . . . . . . . . . . . . . . . . . . . . . . . . 5.6.2 Influence on Downstream Springs and Submarine Springs . . . . . . . 5.6.3 Consequences of Trebišnjica Spring Submergence . . . . . . . . . . . . . 5.6.4 Characteristic Floods of Bilećko and Popov Poljes after 1968 . . . . . 5.6.5 The Role of the Hydrosystem on Flood Mitigation . . . . . . . . . . . . . 5.6.6 Estimation of Consequences of Partial Water Transfer from Catchments of Buna, Bunica and Bregava into Trebišnjica Catchment . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.7 Endemic Species Survival . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.8 Induced Seismicity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.9 Eolian Erosion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 5.10 Importance of Water Potential of Southeast Dinarides . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

293 294 294 295 297 297 300

Chemistry and Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1 Water Quality . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.1 History of Water Protection and Quality Control . . . . . . . . . . . . . . 6.1.2 Results of Water Quality Analysis . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.3 Turbidity . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6.1.4 Self-Purification Capabilities of Karst Underground Flows . . . . . . . 6.2 Water Protection . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . References . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

307 308 308 308 309 312 313 316

300 302 304 304 304 305

About the Author

Petar T. Milanović was born in Belgrade in 1938, where he graduated and received his doctorate from the Geological Department of the Faculty of Mining and Geology, University of Belgrade. He has devoted himself to engineering karstology since the first days of encountering the challenges of the karst phenomenon. More than 50 years, he has worked as an expert for engineering karstology in the Multipurpose HydrosystemTrebišnjica Co. and the Institute for the Utility and Protection of Karst Water in Trebinje (Bosnia and Herzegovina), and later in Energoprojekt Co., Belgrade, Serbia. At the same time, as a university professor, he teaches the course “Applied Hydrogeology of Karst” at the Faculty of Civil Engineering, University of Mostar. After retired, he continues professional activities as freelancer and invited lecturer. As a visiting professor, he visited Colorado State University (1976/77), presented a lecture at the US Geological Survey, Reston; School of Mines, Rapid City; and Alabama State University, Tuscaloosa. As a designer, consultant or auditor, he participated in the realization of a large number of capital projects in the karst of Europe, Asia, Africa and South America. He has published more than a hundred scientific and professional papers on the topic of engineering issues in karst. He was a lecturer in postgraduate studies and, by invitation, at a large number of international scientific and professional gatherings and universities. He is a member of the Governing Board of the International Karst Institute in China, the most important institution of its kind in the world, which was formed under the auspices of UNESCO. He has published several books on engineering karstology, four of which were published by well-known American publishers (Karst Hydrogeology, WRP, 1981; Water Resources Engineering in Karst, CRC Press, 2004; Engineering Karstology of Dams and Reservoirs, CRC Press, 2018; and Dams and Reservoirs in Evaporites, with two coauthors, 2019, Springer). For his contribution to the development of engineering karstology, he has received several national and international awards, including: Award of Honorary Member of the Yugoslav Committee for Hydrogeology and Engineering Geology (1987); Award of Hacettepe University, Ankara (2000); Award for the Development of Karst Science, Beijing (2001); Lifetime Honorary Membership Award of the Association of Speleologists USA (2011); and Presidential Award of the Interna-

xiii

xiv

About the Author

tional Association of Hydrogeologists (2017). For his contribution to the establishment of the University of Mostar and the improvement of scientific teaching and research work, he was awarded a plaque and a diploma (1987). He is president of the Serbian National Committee for Hydrogeology, which is part of the International Association of Hydrogeologists. On the occasion of the 50th anniversary of the establishment of the International Karst Commission, he received a special award as the only representative of Europe (2000).

1

Natural Characteristics

There is no deeper and more thorough karst than that is this one Herzegovina-Montenegrinian between Neretva valley, Skadar Lake and Adriatic Sea. Jovan Cvijić

Irrigation buckets at Trebišnjica River

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. Milanović, Karst of East Herzegovina and Dubrovnik Littoral, Cave and Karst Systems of the World, https://doi.org/10.1007/978-3-031-28120-4_1

1

2

1.1

1

Geographical Position

Area of East Herzegovina (Bosnia and Herzegovina) and Dubrovnik Littoral (Croatia), geologicaly and geomorphologically, belong to the southeastern part of well known Dinaric karst region (Fig. 1.1). This area represents a unique hydrogeological entity. In general it is bordered to the

Fig. 1.1 Area of East Herzegovina and Dubrovnik Littoral

Natural Characteristics

west by the valley of the lower course of the Neretva River, to the south with the coast of the Adriatic Sea, and to the east by the mountain massif of Orjen, that is, a watershed with the catchment of the Boka Kotorska Bay. The northern border is the watershed of the upper Neretva catchment and Drina River catchment (Black Sea catchment).

1.2 History of Studies

Except for a small part in Gatačko Polje, this area as a whole belongs to the Adriatic Sea catchment area. Downstream section of the Neretva River valley, until its delta, and the Adriatic Sea coast from the mouth of the Neretva to the Boka Kotorska Bay, are the lowest erosion base levels for water of all karst aquifers in this region that flows toward them. Area of East Herzegovina encompass surface of 4750 km2.

1.2

History of Studies

Many researchers, especially geologists, geographers, hydrologists, speleologists, biologists, and geophysicists have studied this area and, in their own way, interpreted geomorphological, hydrogeological, hydrological and other karst phenomena and forms. Their observations have been published in various articles and studies and, more recently, through a series of studies from the point of view of practical engineering solutions. Here, the most important project is the regional project—Multipurpose Hydrosystem of Trebišnjica. There are also numerous other projects which address water supply, energy, water management problems, protection of biodiversity, cultural and historical goods, and water potential in this one region. Historically, the oldest known karst phenomenon in this area is Vjetrenica cave. This cave is mentioned in Naturalis Historia written by Gaius Plinius Secundus, 77 AD (Lučić, 2019). In sporadic documents and travelogues from the fifteenth, sixteenth and seventeenth centuries, the floods in Popovo Polje are mentioned. More significant written documents with geological and geographical themes have become more common since the middle of the nineteenth century. At majority of these works, besides some geological data, dominate the description and analysis of the karst phenomenon and struggle with water (problem of floods and droughts). The first data and the first geological sketches of this area were given by A. Boué (1840, 1858 and 1862). Later, there were numerous active Austrian geologists—E. Mojsisowicz, E. Tietze and A. Bittner—who made the first overview geological map in 1880. The first descriptions of some karst phenomena also date from that period. J. Pamučina presented a description of Vjetrenica cave in 1830. Russian diplomat—consul and travelogues A. Hiljferding visited Vjetrenica in 1853. His description of the cave is presented in the book Bosnia, Hercegovina and Old Serbia, which was published in Saint Petersburg in 1873. A slightly more detailed description of this cave was published by H. Mihajlović in the Vjetrenica cave in Zavala, Sarajevo, 1889.

3

M. Groller (1889) in his paper “Das Popovo polje in Herzegovina” analyzes the large flood in this polje in 1883. Philipp Ballif, an Austrian engineering consultant for Bosnia, analyzes the possibility of drainage of Fatničko and Popovo Poljes and organizes the first water level observations. At the same time (1896), he managed the irrigation of Gatačko Polje and construction of the first dam in the Balkans, the Klinje Dam on the Mušnica River, which is still operational. His own activities are described in the publication Wasserbauten in Bosnien und der Hercegowina—I Tele, Meliorationsarbaiten und Cisternen im Karstgebiete which was printed in Vienna in 1896 and displays a first cross section of karst poljes from Gatačko Polje to sea level (Fig. 1.2). Jovan Cvijić visited this area in 1891, 1897, 1908 and, the last time, in 1924 when his health was already quite impaired. Characteristics of karst poljes of East Herzegovina are presented in the article “Karst Poljes of Western Herzegovina”, 1900. In spite of the title mentioning West Herzegovina, the article presents characteristics of the majority of East Herzegovina poljes—Popovo, Fatničko, Dabarsko, Cerničko, Gatačko, Ljubinjsko (Fig. 1.3) and Stolačko, as well as some smaller poljes such as Plana, Meka Gruda and Korita. Cvijić pays special attention to Popova Polje (1909–1926). He organizes the first systematic geomorphological, hydrogeological, hydrological and speleological research (Stevanović & Mijatović, 2005). He presents most of his observations in the work “Old outflows from Popovo Polje and hydrographic zones in the karst”. The results of their own research and analysis of karst in East Herzegovina are summarized by Cvijić in his capital publication Geomorphology II, published in 1926 (Fig. 1.4). The karst area of East Herzegovina was also analyzed by Friedrich Katzer, am Austrian geologist who spent most of his working life in Bosnia and Herzegovina. He presents his observations, analyzes and conclusions in the works “Das Popovo polje in der Herzegovina” and Karst und Karsthydrographie. The first work was published in 1903 Breunschweig, and the second was published in 1909 in Sarajevo. His name is associated with other research, such as water supply of Nevesinje (1915) or occurrences of coal in Nevesinjsko Polje (1921). Popovo Polje and the Trebišnjica River were studied and are mentioned in the works of M. Groller (1889), A. Grund (1903–1910), VJ Daneš (1905, 1906), J. Dedijer (1907), K. Absolon (1916a, 1932), MS Radovanović (1929), S. Milojević (1927a, b, 1928, 1938), A. Chollay and Mr. Chabot (1930).

4

1

Natural Characteristics

Fig. 1.2 Cross section from Gatačko Polje to sea level (Ballif, 1896)

Cvijić’s research continued under Lazić (1926, 1927, 1930, 1932 and 1933) through investigation of caves and shafts in the area of Popovo Polje and underground water connections in the area of East Herzegovina. Numerous speleological objects in the Dubrovnik region have been investigated by Kusijanović (1926). In a few of his articles (1929–1939), he describes caves that were investigated in the vicinity of the Ombla Spring. Geological properties of some individual localities in this one region have been studied by numerous authors: V. Havelka (1931), B. Milojević (1935), J. Mihajlović (1930–1950), K. Petković (1935, 1958, 1961), Z. Bešić

Fig. 1.3 Ljubinjsko Polje, J. Cvijić, Geomorphology II, in 1926

(1951–1959), R. Jovanović (1939–1954), S. Behlilović (1956), M. Vidović (1961), B. Đerković (1966), R. Radojčić (1959–1970) and many others. K. Torbarov and V. Radulović, from 1962 to 1966, prepared a regional hydrogeological map of Montenegro and East Herzegovina in the scale 1:200,000. In the period 1958–1980, sheets of the Basic Geological Map of Yugoslavia were produced in the scale 1:100,000. The area of East Herzegovina is presented in sheets Dubrovnik (B. Marković, 1966), Trebinje (Lj. Natević & V. Petrović, 1970), Nevesinje (V. Rajić, J. Papeš, M. Mojičević et al. 1965–1971) and parts of sheets Ston,

1.2 History of Studies

5

Fig. 1.4 J. Cvijić, portrait and cover page of the book Geomorphology, published in 1926

Metković, Mostar, and Kalinovik (Rajić et al., 1971), as well as parts of Gacko and Nikšić sheets (Mirković et al., 1973). These sheets were a necessary basis for planning geological research works in this area. At the same time, the results of numerous research works studying the needs of the Trebišnjica Hydrosystem significantly contributed to improving the quality of some of these geological maps. The large hydropower potential of this area, as well as the need to protect its karst poljes from flooding, initiated systematic and complex research, with the goal of improving development of the whole region and preventing permanent emigration. Data fromthe mid-1950s showed only 29 inhabitants per square kilometer, which shows extreme underdevelopment of this region. Solving economic underdevelopment of this area was entrusted to the newly founded company, Hydroelectric Power on Trebišnjica (HET), which was formed in Trebinje, and to the design company, Energoinvest, from Sarajevo. To date, the world’s experience with construction of dams and reservoirs in karst has shown a high risk of failure. This area has highly developed karstification. As this problem cannot be avoided, it has to be managed. The development of the region depends on the success of these initiatives. In the mid-1950s, intense investigation of karst in East Herzegovina began: geological, hydrological, hydrogeological, speleological and geophysical. Project documentation and the results of these tests have been published

in a number of professional and scientific works and monographs. Authors include: B. Sikošek (1954), R. Gasparović (1957–1970), O. Zubčević (1959, 1965–1970), S. Mikulec (1960–1975), K. Torbarov (1976). P. Ramljak (1960–1980), D. Aranđelović (1962–1980), J. Mladenović (1963–1975), O. Uzunović (1963), B. Petrović (1965), M. Malez (1954–1970), P. Milanović (1971–2000), M. Milićević (1975–2000), S. Božičević (1984), S. Šićarov (1970–1980), B. Knezević (1976–2016); V. Pješčić (1968–1970), M. Simić (1975), I. Avdagić (1973, 1985), P. Stojić (1980), Ž. Žibret and Z. Šimunić (1976), M. Herak (1971, 1986, 1991), M. Bašagic (1979–1987), I. Bagarić et al., (1980), Kovačina S. & E. Miljković (2004), D. Isailović (1980), V. Jokanović (1980–2005), M. Krasovec (1985–1987), M. Vučić (1975–1985), T. Paviša (1979–1998), R. Buljan (1999) and many others. The karst problems of Nevesinjsko Polje were analysed by I. Bušatlija (1963) and B. Đerković (1966); Gatačko Polje by R. Milojević (1973) and Đ. Ostojić (1980); and geomorphological evolution and neotectonics of Orjen Mountain by Marković (1973). Geological and hydrogeological characteristics of the area of Hutovo Blato were analyzed by Šarin et al., (1965) and Simić (1975). The properties and water management of closed karst poljes was analzsed by Barbalić (1978). Hydrogeological characteristics of the coastal belt were

6

studied by A. Bojanić and D. Ivičić (1948); Konavosko Polje by V. Goatti and B. Biondić (1987); and hydrological characteristics of Ombla Spring by O. Bonacci (1995, 2016). The catalog of earthquakes in this area, for the period 1901–1978, was made by M. Janković and J. Gavrić (1979); induced earthquakes caused by the Bileća Reservoir were analyzed by M. Roksandić (1970) and P. Stojić, (1980). Regional seismotectonic research for defining seismic risk for large structures in the area of the HET was done by M. Arsovski, with associates from the Insitute for Earthquake Enginering (IZIS), Skopje, 1982. Seismic activity and structural relations of the coastal belt were studied by Petković (1935), Prelogović (1975), Cvijanović (1982), Dragašević (1983), Buljan and Prelogović (1997) and numerous others. A comprehensive and detailed explanation of the wide region of Popovo Polje appears in Vjetrenica—view in the soul of Earth, I. Lučić & B. Sket, (2003) and Transformation of karst—History of knowledge of the Dinaric karst on the example of Popovo Polje, I. Lučić (2019). There is significant focus on geological and hydrological characteristics. Exceptionally wealth with underground endemic fauna, especially in Vjetrenica Cave, attracted numerous researchers, including K. Absolon (1916b), J. Hadži (1932), S. Karaman (1953), and E. Pretner (1963). Endemic fauna of the Trebišnjica River basin was studied by S. Čučković (1978), B. Skeet (1976–1983), Pavičević D. & Perreau M. (2008) and many others. In recent years, the Devon Karst Research Society (England) is often present in Trebinje, working on one framework project, “Proteus”. Together with the speleologists from the society Zelena Brda from Trebinje, they conduct research. In 1978, as part of the Hydropower System Trebišnjica, the Institute for Utility and Protection of Karst Water was founded. Its purpose is to study engineering problems in karst, including how to manage great water potential with minimal disruption of specific eco-systems. As part of the Institute, the Laboratory for Water Quality Control was established in the area of East Herzegovina. During the war in the 1990s, the Institute ceaside working; however, the laboratory is still operational. From the extraordinary operational importance for power production is reconfiguration and updating the monitoring system in departement of Power production service. Numerous monitoring stations for registration of precipitation, river flows and fluctuation of underground water level in piezometers are equipped with electronic equipment and connected with a central observation system. Now, the key data are available in real time. Considering the specific regime of underground and surface water under extreme conditions in the Herzegovinian karst, managing the regional water potential becomes more efficient from an energy production viewpoint and with the goal of flood defense.

1

Natural Characteristics

Because of the wealth of data collected over more than 130 years, and numerous successfully built structures in exceptionally developed deep karst, East Herzegovina has become internationally recognised among members of several professions, including engineering karstology. Decades of experience gained during the implementation of the Multipurpose Hydrosystem Trebišnjica, better known as Hidropower System Trebišnjica (HET), is shown in a large number of professional papers and has been presented at numerous professional and scientific meetings. The more significant include: Trebišnjica, Hydropower the system symposium about construction, Trebinje 1965; the YugoslavAmerican project Karst Hydrology and Water Resources (1972–1975), with the participation of leading Yugoslav and American scientists dealing with engineering issues in karst; Symposium of influence of artificial lakes on the environment within the Institute for Utility and Protection of Karst Water, and the Yugoslav Committee for High Dams which was held in Trebinje, 1978; and Water 2020, an international conference about use and water protection, Trebinje, November 2020. As a logical continuation of numerous national and international gatherings held in Trebinje, including the DIKTAS project (UNESCO), there emerged a maintenance international course on engineering karstology, Characterization and Engineering of Karst Aqifers, similar to one from doctoral studies at Belgrade University. The course has been held since 2014 under the leadership of Dr. Z. Stevanovic, Belgrade University, and former chairman of the International Karst Commission, which is part of the International Association of Hydrogeologists. Note: Considering the number of authors who contributed to the knowledge of various aspects of karst in this region, it was not possible to list all their activities, names and references. I appologise to all of them.

1.3

Basic Climatological Data

The climatic characteristics of this region have features of a humid climate, with dry summers and rainy winters. The area between the coastal belt and Popovo Polje is characterized by a Mediterranean climate. Winters are mild, with very rare snowfall precipitation. Summers are warm and dry, with high temperatures. With the distance from the Adriatic coast and an increase in elevation to over 400 m, the climate changes to moderately continental. In areas over elevations of 800 m climate passes into the mountain. Here, the winters are cold and with considerable snow cover, and summers are long and dry. The first climatological and hydrological observations in the area of East Herzegovina began in 1888. The first meteorological station in Trebinje was founded in 1900. With the

1.3 Basic Climatological Data

7

beginning of investigative works for construction of the Hydrosistem Trebišnjica the number of hydrometeorological stations increased rapidly, so that by 1978 their number grew to 47 precipitation, 18 climatological, 4 evaporation and 83 hydrological gauge stations. In the period 1960–1980, an average of about 70 flow measurements was performed per year.

1.3.1

Precipitation

This region is known for its heavy rainfall. Its southeastern area covers part of the Orjen Mountain massif, with the highest recorded rainfall in Europe, more than 8000 mm at its maximum (Fig. 1.5). Precipitation is spatially and temporally distinctly unevenly distributed. The amount of precipitation in the same time interval and over a distance of only a few kilometers can vary more than fivefold and more. October, November and December are extremely wet, with about 40% of the average annual precipitation. Summer (June, July and August) is relatively dry, with a total of 11%

of yearly precipitation. Monthly extremes of precipitation have a large range, from 0 to 754 mm. Maximum precipitation per year in the area of East Herzegovina is close to 5000 mm, measured at the Ubla and Vrbanje stations (slopes of Orjen Mountain). Next to the Orjena area with the largest precipitation are Žabica Mountain, above Dobromani and Velež Mountain in the northwest part of the region. The largest intensity of precipitation in Trebinje was recorded in September 2007–120 mm over 30 min. Average annual precipitation for the Dobromani station in the period from 1923–1939 and 1947–1960 are: Min = 1436 mm, Average = 2164 mm and Max = 4680 mm, that is, by months (Table 1.1): For the Trebinje station, the annual precipitation extremes for the period 1957–1981 are: Min = 1311 mm and Max = 2399 mm. However, the data of measured precipitation for the period 1923–1939 and from 1947–1959 for the same station are different in minimum and maximum values:

Fig. 1.5 Isohyet map and histogram of mean annual precipitation on Orjen Mountain (Milanović, 2004)

Table 1.1 Dobromani, average annual precipitation Month Min Av Max

I 30 201 448

II 45 209 364

III 0 187 410

IV 11 164 468

V 15 111 285

VI 2 79 270

VII 0 47 150

VIII 0 68 387

IX 7 151 329

X 88 265 746

XI 34 349 1030

XII 99 308 1171

8

1

Natural Characteristics

Table 1.2 Trebinje, maximum one-day precipitation Month Av Max

I 64 156

II 71 154

III 60 160

IV 59 146

V 45 132

Min = 860 mm, Average = 1890 mm and Max = 3837 mm Medium and maximum one-day precipitation for the station Trebinje in the period 1925–1940 are presented at Table 1.2. In September of 2012, in Ljubinje, the recorded precipitation was 362 mm for 24 h, along with unconfirmed amounts of water that spilled over the rain gauge. At the highest part of East Herzegovina, Gatačko Polje (station Gacko) measured rainfall for the period 1951–1970 (Table 1.3). The value of yearly rainfall for Gacko station is: Min = 918 mm, Average = 1756 mm and Max = 2513 mm Characteristic and extreme precipitation in October 1998 caused flooding of the Gračanica open coal mine, where the following rainfall was recorded: – 08.10.1998—63.1 mm – 09.10.1998—183.5 mm – 10.10.1998—35.0 mm The maximum precipitation in 24 h was on 08.10.1998 from 00:00 to 24:00 and amounted to 192 mm (registered on the ombrograph). The maximum rainfall for 1 h was registered on October 8, 1998, from 13:00 to 14:00, at 56 mm. The maximum rainfall for 6 h, also on October 8, was 127 mm. On the same day, at 9:00 p.m., a water level of 498 cm at the Srđevići gauge station was recorded, which corresponds to the altitude of 937.21 m.

VI 49 160

VII 24 60

VIII 38 89

IX 50 164

X 90 147

XI 86 140

XII 84 280

The total recorded precipitation from 1968 to 2010, for the period November–February, shows great differences (Table 1.4). In Gatačko and Nevesnjsko Poljes, especially on the surrounding mountains, the duration of precipitation in the form of snow lasts from the beginning of November until May. In the period January–February, the height of the snow cover reaches 150 cm, and often more. In March 2005, in a Gacko urban area, snow height of over 2 m was recorded. Precipitation along the sea coast is much lower than in the continental section. Average annual precipitation for Dubrovnik station is 1006.6 mm. But, even there, precipitation is occasionally significantly higher than simultaneous rainfall in the area of Trebinje or further north. On 02.10.2018, in a period of 6 h, there was 260 mm of precipitation in Dubrovnik; however, in Trebinje there was only 60 mm. Ombrographic measurements show that the maximum intensity of precipitation in East Herzegovina reaches 4 mm/min. An intensity of 1 mm/min may last 20 min.

1.3.2

Air Temperatures

The average annual temperature above 400 m is less than 14 ° C, and below 400 m is higher than 14 °C. Near the sea coast, the average annual temperature is 16 °C. The average annual temperature for the area of Trebinja is 14.1 °C. The coldest month is January, with an average temperature of 5.3 °C, and the warmest month is July, with average

Table 1.3 Gacko, monthly precipitation from 1951–1970 Month Min Av Max Max day

I 4 159 372 60

II 20 192 355 88

III 4 145 392 68

IV 25 122 350 74

V 25 122 272 63

VI 19 95 257 63

VII 19 54 110 48

VIII 10 68 238 91

IX 0 117 371 87

X 0 186 573 130

XI 17 240 423 79

XII 55 256 636 85

Table 1.4 Precipitation, November–February, 1968–2010 Area (rain gauge) Trebinje Bileća Gacko

November 1974–February 1975 272.2 mm 281.9 mm 348.9 mm

November 2009–February 2010 1268.7 mm 1269.9 mm 1400.0 mm

1.3 Basic Climatological Data

9

temperature of 23.3 °C. The absolute recorded maximum is 39.5 °C, and the absolute recorded minimum is -10.0 °C. The coldest area in East Herzegovina is Gacko. The absolute minimum of -29.6 °C was measured in 1967.

1.3.3

Relative Humidity and Evaporation

The average annual humidity is 65.8%, and the highest average monthly humidity is in November—73.3%. The range of minimum relative humidity for January is 11%– 43%. Evaporation measurements were made at the Hutovo and Bileća reservoirs. Table 1.5 shows that in the observed period from April to October (1981), evaporation was greatest in July and August.

1.3.4

Hydrological Characteristics

From a hydrological point of view, the watersheds of East Herzegovina have all the typical characteristics of the hydrology of karst areas. The surface hydrographic network of permanent character is ultimately reduced. Surface outflow is distinctly temporary. Permanent natural surface lakes do not exist, but all karst poljes and individual smaller karst depressions temporarily flood, performing the function of natural retention. Under natural conditions, floods are recorded in all karst poljes. A graphic presentation of flood duration in the Popovo, Dabarsko and Fatničko poljes is given in Fig. 1.6. Analyzing the characteristics of water management systems of closed karst poljes, Z. Barbalić (1976) states that retention of closed poljes has a very significant influence on the general hydrological regime in wider areas. This retention contributes to the water balance, thus, exerts a very positive role on the regime of outflow from the lower poljes. In addition, some natural retention has a significant impact on the general piezometric conditions underground. The first hydrological gauge station was established in 1888. Systematic water level monitoring at gauge stations then began: Dražin do, Dobri do (Popovo Polje), Zavala, Trebinje, Arslanagića bridge, Bileća, Dabarsko Polje (Kuti and Bijeljani), Fatničko Polje and Gračanica (Gatačko Polje). A water gauging station, Srđevići (Gatačko Polje), was established in 1892, and Dobromani (Popovo Polje) and Bugovina (Mokro Polje) were established in 1898.

The first precipitation stations in Bileća and Gacko were established in 1892. Despite the fact that an average of over 70 hydrological measurements were performed annually, in some years over 120 measurements, current hydrological data are still subject to change and corrections. From the average annualy 367 m3/s of water from the precipitation on the East Herzegovina area only 145.4 m3/ s can be controlled by surface gauge stations, i.e. approx 40% of the total precipitation. That fact indicates very complicated regional hydrological relations (Mikulec, 1972). The average specific outflow is 40–50 l/s/km2. The most significant flows are from the Trebišnjica, Zalomka, Bregava, Buna and Mušnica rivers, with the Gračanica tributary. The Trebišnjica, Zalomka and Bregava rivers flow along their entire length only in wet periods. In dry periods, the Trebišnjica dries up downstream from Trebinje, the Zalomka near Crni Kuk, and the Bregava upstream from the Bitunje Spring and downstream from the Stolac urban area. Flows which do not dry up and flow the whole length are Mušnica, Sušica, Buna with tributary Bunica, Krupa and Dubrovnik rivers. The Dubrovnik river flow is under direct and strong influence of the sea, so it can only conditionally be treated as river flow. The Ključka River in Cerničko Polje and the Vrijeka in the Dabarsko Polje have permanent flows. These are flows with large capacity in winter (Q > 20 m3/s), and with practically negligible flows in the summer, most often between 100 and 150 l/s, up to extremely small flows under 50 l/s. The flow of Ključka Rijeka is interesting, with an entire length of about 300 m. Flows which dry up along the whole length are the Brova in Ljubomirsko Polje and Bukov Creek, which started in the dolomites of Bukov do (Krtinje), east of Ljubinjsko Polje. At extremely high water levels, the flow of the Trebišnjica River at a section downstream from the Gorica area has reached 940 m3/s (October 23. 1939). At the gauge station in Dobromani (Popovo Polje), on several occasions, the measured flow was over 1000 m3/s. For instance, on 02.12.1903 the measured flow was 1362 m3/s; on 24.03.1915 it was 1307 m3/s; and on 01.03.1945 the flow was 1065 m3/s. As a consequence of extreme precipitation in 1971, the flood waters submerged the limnigraph at the Dobromani gauge station (the depth of water in the river bed was 8 m).

Table 1.5 Monthly evaporation from reservoir surface (mm) Hutovo Bileća

IV 80.22 71.54

V 105.00 89.95

VI 117.39 103.18

VII 153.65 136.71

VIII 137.97 127.40

IX 72.10 72.45

X 36.19 45.64

10

1

Natural Characteristics

Fig. 1.6 Flood duration in Popovo, Fatničko and Dabarsko poljes. (courtesy Energoinvest 1971)

The minimum flow through the river section Gorica is about 3 m3/s. The flow of the Trebišnjica River is drying up downstream from Trebinje urban area, most often near Dražin do, while it is without flow at the Dobromani gauge station in the dry period. The longest floods were registered in Popovo Polje in 1915 (303 days) and 1937 (271 days). The shortest flooding was recorded in 1930, when the polje was submerged for 204 days. During the average wet year, floods last about 240 days and had a maximum height of about 34 m (Fig. 1.7).

Fig. 1.7 The flood in Popova Polje 1971 (Photo Balić)

According to the calculations of the Austrian major Groler, during the flood in 1883 in Popovo Polje, 356.5 million m3 of water accumulated. All this water sank through a number of ponors within 56 days. It is calculated that during the maximum floods in the polje, close to 1 billion m3 of water accumulated. Under natural conditions, the flood water runoff from all karst poljes is possible only through numerous ponors (swallow holes) and underground karst channels. The exception is Trebinjsko Polje, from where a large amount of the water

1.4 Geological Characteristics

11

As a consequence of the Bileća Reservoir, the duration of floods in Fatničko Polje increased. Data on the duration of floods after the construction of the Grančarevo Dam and the Bileća reservoir are given in Sects. 1.6.7 and 5.6.3. It is interesting to note that during the great flood of 1934 and submergence of the Biograd Ponor, the flood water from Nevesinjsko Polje overflowed above the limestone ridge, creating a huge torrent flow along the Dabrica valley and a temporary flow in the river bed of Radimlja (Fig. 2.21). Floods in Gradac Polje are rare and last a short time. More detailed descriptions of the hydrological characteristics of river courses and karst poljes of East Herzegovina are given in the chapters Karst poljes (1.6) and catchment areas, surface flows and springs (Chap. 2).

1.4

Geological Characteristics

1.4.1

Lithostratigraphic Characteristics

The analysed sub-region includes the extensive MesozoicTertiary complex of the Dinaric Mountain (Dinarides) (Fig. 1.9). The lithologically relatively monotonous and distinctly sedimentary complex possesses all the characteristics of the geological authenticity of the Outher Dinarides to which it belongs. The rock masses that dominate regionally are Mesozoic limestone and dolomites. These sediments form the basic geological setting of the region. Tertiary sediment, limestone, claystone, sandstone and conglomerates, as well as Quaternary cover, have a much lower percentage.

Fig. 1.8 The relationship of flood level (H) and cumulative swallow capacity (Qg) for the Popovo, Fatničko, Dabarsko and Gatačko poljes, 1969 (according to Energoinvest)

flows on the surface, through the Trebišnjica riverbed, towards Popovo Polje. Diagrams of the cumulative absorption of the ponors in the Popovo, Fatničko, Dabarsko and Gatačko poljes are presented in Fig. 1.8. The largest individual ponor is Biograd is Nevesinjsko Polje, with a swallowing capacity of about 110 m3/s. With construction of the Hydrosystem Trebišnjica, especially the construction of RPP Čapljina, floods in Popovo Polje have been significantly reduced but not completely eliminated in the lowest part.

Triassic The sediments of the Triassic age are found across a few localities comprising a small part of East Herzegovina. The thick-bedded and plate dolomites of the Upper Triassic period (including the sediments of the flysch facies) are the most important formation that comprises the main overthrust known as the High Karst Overthrust. In this long, thin and sometimes tectonically interrupted zone, lences and laminated dolomitic breccia are recorded at some locations. In the catchments of the Sušica River, Lastva and Jasen, the Upper Triassic formations are represented by layers of dolomite with different thicknesses. These dolomites are intensively grussified (crushed, sometime powderised) locally, more than 100 m in depth. In the area of Lastva and Grančarevo, the older parts of this formation are composed of shale with coal. The presence of the continental facies with the admixture of coal shows the periodicity of the tectonic activity. The total thickness of the Triassic sediments varies between 450 and 950 m.

12

1

Natural Characteristics

Fig. 1.9 Dinaric karst region: 1. Slovenia, 2. Croatia, 3. West Bosnia, 4. West Herzegovina, 5. East Herzegovina, 6. Montenegro, and 7. Serbia (Milanović, 2006)

The Upper Triassic formations of massive and layered dolomites are developed in the Zalomka valley between Gradina, Fojnica and Rilje. As is the case with the Triassic dolomites in the Lastva area, in the same manner, the Zalomka dolomites also form the core of the anticline. A narrow zone of Upper Triassic dolomites is noted at the Morine plateau, north of village Kifino Selo. Jurassic Jurassic sediments are more frequent than Triassic sediments. There are three distinct zones, and a couple of smaller localities with sediments of the Jurassic age. The first zone is divided into offshore areas along the High Karst Overthrust. This is a long zone with a general dinaric direction, in which the Triassic sediments gradually change into a Jurassic formation. The Lias is represented by a mixture of dolomite, dolomitic limestone and limestone. North of Konavli Polje, the zones and lences are formed mainly of limestone with lithiotis, which sometimes form true lumacels. The Middle Jurassic Cretaceous sediment lies normally over the Liassic formation. Dolomites also occur in this formation. The Oxfordian and Lower Kimeridgian limestone normally follow a continuous ‘ribbon’ of the Doger formation. In the Upper Kimeridgian and Titonian, they are represented by a

series of limestone and dolomite. The complete package of this Jurassic zone is located in the Duži area (from Neum), and its greatest extent is in the Gromače anticline zone, north of the Dubrovačka Rijeka and Zaton, where it forms part of a large karst plateau. The other major area with Jurassic sediments is composed of two separated zones, one at Grančrevo village and the second in the area of the Arslanagića Bridge. The lithiotic limestone and dolomite with shale interbeds, and the admixture of coal-bearing material in the north-west area of the Lastava Anticline, are particularly well studied. The Liasic formation, thin to thick stratified beds of lithiotic limestone, are the most exposed sediments of the Lower Jurassic age and are exposed from the Grančarevo area and through Jasen, continuing along the northern periphery of Ljubomirsko Polje. Their composition consists of dolomitic, microcrystalline and crystalline limestone. In a few localities, layered dolomites lie over the lithiotic limestone (Ljubomir, Fig. 1.10a). The limestone of Doger and Malm lie normally over the Liasic and is divided into Dubočani-Budoši-Krtinje areas. In the Malm limestone, on the north-eastern perimeter of Ljubomirsko Polje, from Jasen to Krtinje, there are a number of localities containing bauxite.

1.4 Geological Characteristics

13

Fig. 1.10 (a) Print of fish at thin layered Jurassic dolomites in Ljubomirsko Polje (b) Part of hippurites from Cretaceous limestone in the area of Gradac Polje, 1971 (Photo Milanović, 1971)

The third area with Jurassic sediments is located in the northern part of East Herzegovina and includes the Bjelasnica Mountain, part of the Zalomka River catchment area and the mountain area at the north-eastern perimeter of Nevesinjsko Polje. Lijasic and Doger are represented in the Zalomka area between Kokorinsky brook and Morine plateau. They are represented by limestone, dolomite, chert and silicious shaly limestone. Near Rilja, the upper part of the Liassicdoger formations are composed of oolitic and pseudo-oolitic limestone, as well as bedded dolomite and chert. The Lijassic-Doger formation in the Zalomka River area is characterised by distinct facial change in a small area. The special significance of this stratigraphic unit is given by the chert, which can be in form of lences, or laminated layers, or in mugla shape. In the Bjelasnica area, the Liassic-Doger sediments form one smaller area in the facies of different types of limestone, which are dominated, particularly in higher areas, by oolitic and pseudo-oolitic limestone. Sediments of the Upper Jurassic age are found in the Bjelasnica area and in the anticlinal structure of Zalomka, where it lies normally over the Doger formation. This zone extends through Rilje and Plužine to the perimeter of Nevesinjsko Polje in the Bijenja area. It consists of wellbedded Oxfordian-Kimmeridgian limestone and dolomite, locally with chert intercalation. They are normally overlain by layered Kimmeridgian-portland sediments. They are in various locations of different lithological composition. In the Kunjak-Plužine-Bijenja area, these are dense crystalline limestone; in the southern Bjelasnica foothills, they are limestone with interbedded dolomite lenses and intercalations of shaly limestone; on the Baba Mountain, the dense limestone

breaks off into the oolitic limestone facies, with thin interbeds of dolomite; in the area between Ključ and Bjelasnica, it is in the facies of thick bedded limestone; and in the area between Lukovice and Gradina, the Portland-Kimmeridgian is developed in the limestone cherty facies. Cretaceous No doubt Cretaceous sediments are the most abundant stratigraphic member in the area of East Herzegovina and the Dubrovnik Littoral. They are estimated to cover over 60% of this area and, in relation to other sediments, they dominate both in terms of the area they cover and in terms of thickness. This is generally the case in the Upper Cretaceous, whereas the Lower Cretaceous is much thinner. The Lower Cretaceous is represented in the offshore area and lies over the Jurassic sediments. This geological formation is long, narrow and locally disconnected by tectonic movemnet. It continues from the Neretva River Delta over Zavala, Hum, Duži and Stravča toward the Boka Kotorska Bay. In the Stravča area, this zone is disconnected by a regional transversal fault zone. This zone consists of well-bedded limestone and dolomite. The smallest areas built up from these sediments are also found in the area of the Grab village and in the Leotar Mountain area. In the northernmost wing of the Lastva anticline, Cretaceous limestone is deposited on massive and thick-bedded dolomites, so that the upper parts (apt-alb) are dominated by thin-bedded and layered limestone. In the northern part of the region, they lie concordantly above the Upper Jurassic sediments. This is the LukoviceBjelasnica-Šipačno-Ključ subdivision. The rock mass consists of dolomite, dolomitic limestone and limestone, with occurrences of bituminous limestone. Sediments of the

14

Lower Cretaceous age are also found in the Bregava River area. The lower parts consist of microcrystalline limestone, and the upper parts of dolomites and dolomitic limestone. Upper Cretaceous sediments cover the broad area of East Herzegovina. It is characterised by the occurrence of numerous hipurites (Fig. 1.10b). It is developed in the limestone— dolomitic and clastic facies. Al stage ages of Upper Cretaceous are confirmed. It is evenly distributed throughout the region, but it is difficult to identify all localities when geographically identifying its distribution. Cenoman is found in the Zupci-Ubla area, around Dražin do, in the Lastva anticline, eastern of the village of Meka Gruda and in the Bregava River valley. It is built mainly of cryptocrystalline limestone, interspersed with rare dolomite interbeds. The sediments of the Turonian age have an extremely wide distribution. They are developed as a broad zone between the Popovo and Ljubomirsko Poljes (limestone with dolomites, especially in the lower parts but also plate dolomites with interbedded limestone and limestone with chondrodontes). The Turonian formation is also developed in the area of Ubla and in higher developed zones on the southern slopes of the Žaba Mountain. In a large area north of the town of Bileća, the Cenomanian and Turonian formations are not separated. The same is also true for part of the Velež Mountain. The upper parts of the Turonian are composed of thick-bedded and massive limestone with rudist, cryptocrystalline and microcrystalline structures of light yellow color. Information presented as a textual explanation of the geological sheet Trebinje concludes: “. . .area that consists of these limestones is most intensively karstified in this part of Outher Dinarides” (Natević, 1970). The CaCO3 content is 99%. Sediments of the Senonian age are represented by cryptocrystalline shaly limestone with rudist. In the offshore area and on the islands, the Senonian formations are developed in dolomitic and crystalline limestone facies. There are some large areas of predominantly thick-bedded and massive limestone of the Senonian age. This is the terrain around the Ljubinje urban area and between the Ljubinjsko and Popovo Poljes up to the Neretva valley, with the Dinaric trend of structures. The Senonian formations are developed north of Fatničko Polje and south of Lukavačko Polje. It builds the southern perimeter of Dabarsko Polje and it extends from Trusina Mountain to the Neretva valley. It builds the southwestern slopes of the Velež Mountain and the perimeter of the wetlend Hutovo Blato (Derane and Svitava depressions). The basic characteristic of this limestone is the great numbers of rudist. In the Dabrica and Udrežnje region, at the contact between the Senonian limestone and the limestone breccia, there are significant deposits of bauxite. The Upper Cretaceous facies, which builds up significant areas of the northernmost part of the region, is developed in

1

Natural Characteristics

the limestone-shaly and the shaly-sand facies. This is the product of the well-known Durmitor Flysch zone. The overlying subdivision is a part of the deposits which divide the High Karst Overthrust unit from the unit of palaeozoic shists and limestone between Gatačko Polje and the Borač area in the north-east, to Morinj and Plužine in the west. The basis of clastic deposits has poorly defined characteristics of the flysch formation. It is composed of limestone breccia, conglomerates and shaly limestone, with interlayers of laminated mudstone and shale. The breccia and conglomerates are less represented than the limestone, and source of its origin is resedimentation of Titonian and Turronian rocks. Over these sediments lies a detachment with shales, shaly limestone and calcarenites, which are alternately exchanged with limestone breccia and conglomerates. These sediments have some of the most distinct characteristics of flysch. The following young lithological member has all the characteristics of a true flysch. It consists of sandstones, shale, sandy limestone, calcarenites and conglomerates, with frequent gradual transformation between the strata. Tertiary Palaeogene formations are registered in more separated localities of this region: the narrow littoral belt, the Hutovo Blato wetland; the wider area of Stolac and Svitava, the Dabrica area and Trusina Mountain, the narrow and frequently disconnected strips in the direction of the Ljeskov dub—Pusto Polje, the perimeter of Slato Polje—the southern slope of Đed Mountain—Cerničko Polje, and the along the northern perimeter of Dabarsko and Fatničko Poljes. Sediments of the Palaeocene, Eocene and Oligocene age that form a part of the para-autochthonous sedimentary deposits extend in the shape of locally disconnected strips along the Adriatic coast, which is widening in the subareas of Slano, Dubrovačka Župa and Konavali. The main components are alveoline-nummulitic limestone and flysch sediments (shale, claystone, clayey sandstone). The Cretaceous-Paleocene transitional zone is developed in the direction of the Dubrovačka Rijeka—Cavtat—Sutorina in a facies of clayey limestone. The Palaeocene-Eocene limestone is sporadically recorded between the Dubrovačka Rijeka and the Zaton, and from a long, narrow strip in the coastal zone between the Pelješac and the Neretva River delta. The middle Eocene of the autochthonous part of the structure is composed of nummulitic limestone, and the immediate zone on the surface along the overthrust head is composed of sediments of flysch age (Eocene-Oligocene). These sediments consist of sandstones, sandy shales and claystones. These sediments are detected in Dubrovačka Župa, Konavosko Polje and Sutorina in Boka Kotorska Bay.

1.4 Geological Characteristics

Upper Eocene flysch is found along the High Karst Owerthrust following the line Raba—Slano—Orašac— Zaton—Komolac—Brgat. This zone is sporadically dissected. The allochthonous part of the structure in the facies of Triassic dolomite is overthrusted over the flysch. In the wider region of Stolac and Svitava, the palaeogene sediments consist of Liburian strata, alveoline-nummulitic limestone and Eocene clastic deposits. Dark limestone (PcE), so-called Liburian strata that lie discordantly over the rudist limestone, are found along the reverse faults. The large zone of these rudistic limestones is located in the area of Dabrica— Dabarsko Polje and in the vicinity of Ubosko. At theprocess of gradually change, they are replaced by alveolinenummolitic limestone of the Lower and Middle Eocene. They form a wide zone, elongated in the Dinaric direction, Bivolje Brdo—Stolac and are also found in the Dabarsko Polje area. The clastic sediments are registered in the area of Opličići, Domanovići, Masline-Lokve, Dabrica and at a few more small localities. These sediments consist of conglomerates, sandstones, shales and clay. At the contact between the Eocene alveoline-nummulitic limestone and the Eocene conglomerates in the area of Stolac, Bivolje Brdo and Domanovići, there are occurrences and deposits of bauxite. The Eocene flysch of Lukavačko and Fatničko Poljes is represented by conglomerates, limestone breccia, sandstone, shale and shaly limestone. Paleogene conglomerates consist of a large area in the north-western part of East Herzegovina (in the region of Nevesinjsko, Slato and Lukavačko Poljes). Thick masses of these conglomerates are deposited in the Trusina Mountain area and extend to the Dabrica area. Some deposits are noted south of Cerničko Polje and north of Gatačko Polje, around Gračanica creek and the village of Nadinići. The conglomerates are composed of pieces of different sizes (from a diameter of a few millimeters up to blocks of over 1 m), different ages (from the Triassic to the Eocene) and different lithological composition. The majority are carbonates; however, some pebbles of eruptive rocks were found. In the conglomerate series, shaly sediments are also deposited, which appear on the surface in the Zovidolka River area. Neogene sediments are found in three localities, in Gatačko and Nevesinjsko Poljes and north of Stolac, near Hodovo and Rotimlje. The thickness of the Neogene rock in Gatačko Polje is estimated at 400 m. This is a coal-bearing series of three coal layers. The Neogene sediments in Nevesinjsko Polje contain yellow-gray clay and clayey shaly sediments, with three seams of pure quality coal. In the Hodovo area, the Neogene is composed of yellow-gray and gray shale, with low grain conglomerates and shale with clay lamination. Coal (lignite) is also present in this deposit.

15

Quaternary The quaternary formations cover a considerable area. This formation consists of unconsolidated rocks that cover karst poljes, river valleys, and sinkhole bottoms, as well as slope breccias, talus, and moraine material. Alluvial sediments cover the valleys of the Zalomka, Bregava, Buna, Neretva and Trebišnjica rivers. These are gravel, and sands with loam. The same material, with variations in granulation, is deposited in karst poljes. Proluvial deposits are found in Svitava, near Stolac in Ljubinjsko and Ljubomirsko Poljes. Limnoglacial sediments are found in the Ubla—Zupci area and in part of Nevesinjsko Polje. Fluvioglacial deposits cover the Zupci plateau and part of Mokro Polje. Terra rossa covers the bottoms of practically all uvalas and sinkholes in the region. Clay is present in the sediments deposited on the surface and in the sediments deposited in karst channels and caverns. Their quantity in the sedimentary rock mass of the Dinarides area is not massive; however, in terms of engineering karstology (for instance during grouting procedure), as well as in the case of water quality, their presence may be the source of major problems. All sedimentary rocks contain a clayey fraction of at least 3% (Osipov & Sokolov, 2013). Clays are formed by physical-chemical processes on the surface and in the subsurface, from the deepest parts of the ocean floor to the highest mountain massifs covered by glaciers. The process is caused by mechanical fragmentation of the rock, and it continues by the chemical process or as a consequence of change in mineralogical composition, structure and texture of the rock matrix by denudation or sedimentation and is completed by the process of lithification. Water plays a key role in their genesis and transport. The process of clay deposition in the underground and their sedimentation are linked to erosion and deposition from the underground, with different intensity. In the karst underground, a huge amount of clay is deposited, ranging from pure and plastic up to partially or completely lithified. Sediments belonging to the thinnest (0.002 mm) and colloidal (0.0002 mm) fractions are easily transported to the deepest parts of the karstified rock mass. Even if in common comunication is mostly used term clay should keep in the mine that it is never mineralogical absolutely pure. Almost alvays it consists no-clayey components sometime procentually more than clay itself. Plasticity increases with an increase of the clay component. A large amount of clay in this part of Dinarides is of glaciogenic origin, transported by fluvioglacial flows and deposited together with the much larger fraction. Part of the clay is also formed in the subsurface from the epikarst zone to a depth of more than 2 km along the tectonic zones (milonitic

16

1

zones). The fragmentation of the rock mass is also caused by turbulent flows with high kinetic energy or by the process of erosion and evorsion (so-called “water mill” effect). The clays are deposited in the Neogene and Limnoglacial sediments of the karst poljes of East Herzegovina and, in a large percentage, together with the sandy-dusty carbonate fraction, are deposited in a number of caverns, karst channels and fissures. Of the non-clayey components, apart from carbonate, clay incorporates negligible content of Uranium (U) and Thorium (Th). Clay deposits are a major problem for tunnel excavation and are the main cause of construction setbacks. It is especially technologically complicated to pass through caverns filled with clay when the tunnel is excavated with a tunnel boring machine (TBM). Except for water bursts and floods during excavation of the tunnel Fatnica—Bileća, the caverns filled with clayey deposits were the most frequent and main source of work delay. The large quantities of clay deposited in Mokro Polje are derived from fluvioglacial currents formed by the melting of the Orjen glaciers. They are used as basic raw material for construction of the clay-cement grout curtain beneath the Grančarevo Dam. In submerged caverns with slow water flow, the most saturated fraction and colloidal particles are melted. Thus, in the caverns inside limestone ridge Ljut (between Dabarsko and Fatničko Poljes), along the route of the Dabar-Fatnica tunnel, large quantities (a few hundred cubic metres, maybe more) of very clean and plastic clay are deposited. The presence of clay in the water endangers the quality of the water because it is the cause of increased turbidity of water in karst springs used for water supply. The origin of turbidity in karst water is discussed in more detail in Chap. 6.

1.4.2

Regional Forms of Tectonic Composition

For a change from the monotonous lithological composition, analyzed ground is characterized by very complex tectonic relationships. Based exclusively on field observations, the basic geotectonic scheme was given by Petković (1935, 1958). Most significantly, he defines the tectonic structure along this part of the Adriatic coast as the front of the High Karst Overthrust. Numerous neotectonic and seismo-tectonic data and structural analyses indicated the role of movement of the Adriatic microplate under the Dinarides (Prelogović, 1975; Dragašević, 1983; Prelogović & Kranjec, 1983; Aljinović et al., 1987). According to the new regional structural scheme presented by M. Herak (1991), the key structural units are Adriatic, Dinaric and Epiadriatic.

Natural Characteristics

In addition to the numerous data on which the mentioned authors based their conclusions, this opinion is supported by the results of seismic tests in the exploratory galleries inside the regional overthrust in the area of Ombla Spring near Dubrovnik. The velocity of seismic waves in the rock mass, measured on several occasions, was on average 6650 m/s, and locally close to 8000 m/s. It indicates the extreme pressures to which the northern carbonate block in the contact area was exposed to from the forces of the Adriatic microplate. As a consequence of this scenario, rotation of carbonate blocks between zones of contact along the coast and Popovo Polje occur. Uplifting and rotation of regional structures undoubtedly influenced the formation of these tectonic, geomorphological and hydrogeological characteristics. For a long time, the basic document for the regional and detailed analysis of tectonic structures was a geological map and, later, aerial photos. Satellite images were also used, once they became available. In addition to standard and commercial aerial photos, a large part of East Herzegovina was covered by low-flight plane photos as a basis for making detailed geological maps for areas of construction and different large structures. For design of seepage waterproofing technology along the pervious Trebišnjica riverbed, the entire Popovo Polje was covered by aerial photos, scale 1:5000. Tectonic and karst features that registered on the aerial photographs were checked during geological mapping in the field. Characteristics of faults and overthrusts at zones of future structures are determined by application of geophysical methods and exploratory drilling. For the Upper Horizons project, which is part of the regional Hydrosystem Trebišnjica Project, aerial photography of Nevesinjsko Polje and the Zalomka River valley was organized. The tectonic mosaic of this region is built by the structures of faults, overthrusts and local imbricated structures, all of them coupled into the large units formingregional structures, with general dinaric strike. From the results of recent investigations, the opinion that existence of large overthrusts, with thrust movement of more than 10 km, is questionable. Dominating elements of geological structures in this region are submarine discontinuity close by and parallel with the sea coast (subduction zone between Adriatic microplates and Dinarides) and discontinuities of longitudinal direction which are clearly noticeable on satellite images and confirmed by geological mapping. The most significant among them include: the head of the High Karst Overthrust and tectonic lines Grahovo-Ljubomir-Stolac to the Neretva River valley upstream from the mouth of Bregava; Plana— Fatnica—Dabarsko Polje—Buna and Pusto Polje-SrđevićiGradina-Zalom-Bijenja, which divide the entire region into more tectonic blocks with dinaric strike.

1.4 Geological Characteristics

Along the above-defined discontinuties, it is possible to divide into five regional structural blocks: 1. 2. 3. 4. 5.

Block para-autochthonous (Adriatic) High Karst Overthrust (Dinarik) structural block Lastva structural block Velež-Meka Gruda structure Zalomka structure

In a series of local anticlinal structures within these structural blocks, such as the Gromača, Dobri do, Ljubova, Bjelasnica and Zalomka anticline, undoubtedly the most significant is the Lastva anticline, from a regional hydrogeological aspect. It is made up of not continual recumbent fault that is partially overthrusted over adjacent, southwestern, tectonic units along the Zupci-Ljubomir fault zone. The anticline core consists of Triassic dolomites of hectometer thickness. In comparison, the southwestern anticline limb is under the influence of strong horizontal stress and demolition of the structure, and the northeast limb has a more regular shape with preserved stratigraphic sequence. Among the majority of transversal faults of regional importance are the Zupci and Slivnica faults. The Zupci fault was observed, analyzed and described by Cvijić (1924). It is actually a fault zone more than 30 km long that stretches along the western edge of Orjen Mountain and Molunat, across Dubravka, Grab, around the edge of the Zupci plateau, then cuts across the Trebišnjica River downstream from the Oko Spring and continues towards Ljubomirsko Polje. In the area of Ljubomirsko Polje, this zone merges with the regional Grahovo-Stolac fault. The width of the Zupci fault zone is locally over 100 m. According to S. Behlilović (1956), the Cretaceous sediments along this zone are displaced by about 1000 m. The broad Plat—Duži fault zone, better known as the Slivnički fault, crosses Popovo Polje and the Trebišnjica riverbed and continues toward Ljubomirsko Polje but with simple tectonic discontinuity, without expressed wide crushing zones. On the geological maps, in the area of Trebinje and Nevesinje, a large number of transverse faults running north-south were noted. These are often regional faults with considerable length. Predominantly, these faults are vertical or semi-vertical. They cut through the folded structures in the Dinaric direction and break tectonic homogeneity of larger units in separate blocks. Lastva anticline Exceptionally significant hydrogeological role in karst aquifer evolution process and associated catchments of the Trebišnjica regional basin have so-called Lastva anticline structure, which is formed in the east (raised) block along the regional Zupci fault zone. The compressed

17

core of this regional fold consists of Triassic, Jurassic and Cretaceous dolomites. They are mostly affected by the process of disintegration (grussification). This makes them partially to absolutely waterproof. They take hold of a wide zone between Grančarevo and the Arslanagić bridge and stretch across the Jasen, Mosko and Ljubomirsko Poljes, and continue along fault zones northeast from Ljubinjsko Polje (anticline Žrvanj with dolomites in core). Further, according to direction of the northwest and Bregava Springs, this one structure has formed a fault without elements of folding or reverse movements. The Zupci fault zone and Lastva anticline represent the most significant hydrogeological structure and act as barriers between the northern and southern parts of Trebišnjica and Bregava catchments. Northeast from Ljubinjrsko Polje, dolomites of the Lower Cretaceous in the core of the Žrvanj anticline represent a barrier (watershed) for water that sinks in Fatničko Polje and directs them toward the Trebišnjica valley.

1.4.3

Seismicity

Undoubtedly, some older tectonic discontinuity is not definitely finished. This is confirmed by activity of the most significant seismogenic localities in this region near Dubrovnik, Boka Kotorska, Ston, estuary Neretva and Stolac. For instance, southeast of Stolac in the last 100 years, a greater number of earthquakes with a magnitude greater than 4.0 were registered. The strongest of these earthquakes had a magnitude of 6.0, and the depth of the hypocenter was 17 km (Janković and Gavrić, 1979). The most significant active seismogenic zone is represented by the coastal submarine fault, along which large catastrophic earthquakes occurred: 367, 1520, 1667, 1780, 1843, 1844, 1853, and the last one in 1979. Based on the devastating effect on the surface terrain, evaluated magnitude of these earthquakes was between 6.5 and 7.0 by Richter (Cvijanović, 1982). According to the same author, “initial tectonic movements, directed towards the northwest and north from the Adriatic area towards the Dinarides are on the level of Mohorovići’s discontinuity or even deeper. Movement of the Adriatic microplate according to land brings first of all subduction under Dinarides, then to compression of rock mass the above Mohorovičić’s discontinuity, folding, reverse faulting and overtrhrusting”. In the area of the Adriatic depression, the depth of Mohorovičić discontinuity is about 30 km. In the direction of the north (mainland) it increases. According to data of deep seismic sounding, in the Gacko area it is at a depth of 40–45 km. Of all those mentioned, the most famous earthquakes are most certainly the earthquake that occurred in 1667 and destroyed Dubrovnik and the earthquake on the Montenegro

18

1

coast in 1979. The main parameters of the earthquake that occurred on 15.04.1979 are: M = 6.6 and hypocenter depth H = 20 km, with the epicenter between Ulcinj and Kotor (Vukašinović et al., 1979). Based on measurement data, it was estimated that the anhydrite bodies in the seabed in the Dubrovnik area are located at depths of 4–5 km. Their connection with the zone of high destruction, in the area of the Adriatic shelf, is confirmed by the data on the occurrence of H2 S in the area of Mokošica. Also, on the surface of the sea, between Molunat and Cavtat, the next one the day after the earthquake in the Montenegro littoral (1979), felt intensely the presence of H2 S. With construction of large man-made reservoirs, exceptionally important is induced seismicity which, in karstified rocks, has certain specificity. A short explanation is presented in Chap. 5.

1.4.4

Hydrogeological Aspects of Neotectonic Activities

The general trend of rock mass vertical movement during the neotectonic period was not at the same intensity in the entire area of East Herzegovina. Sinking and rising processes in the framework of a general trend have relative values. Morphostructural units were delineated by tectonic discontinuities. Undoubtedly, subduction of the Adriatic microplate, which is still active today, has a great impact on the disorganization of surface river net and evolution of the karst process, but not in the coastal area only. This process is equally active in the deep hinterland. In this way, neotectonic activity has direct influence on direction of karst aquifer evolution processes. According to effect and mean activity of existing hydrogeological characteristics, the karst aquifer evolution process can be devided into two global stages: 1. Presavian (before Miocene) and 2. Neotectonic, which has two time periods: – Pliocene—Pleistocene – Pleistocene end—the present The Presavian stage of karstification had an insignificant influence on the current state of the karst aquifer. In the Triassic—Upper Cretaceous period, the parts of carbonate complex increased a few times above the level of sedimentation basins, making possible the development of the karst process. Relics of this process exist within the framework of recent karst aquifer as paleokarst forms filled with bauxite. This one period ends with orogenic movements known as middle alpine orogenic phases. This movement is expressed with compressive discontinuites and by emersion of

Natural Characteristics

carbonate masses that are captured by the process of karstification during neotectonic phases of development. Strong horizontal and subhorizontal pressures in a SE-SSW direction result in numerous folded structures that consist of Mesozoic and Paleogene sediments. The tectogenetic process that starts during the Laramie phase culminates at the end of the Eocene (Pyrenean and Savian orogenic phase), when the basic elements of the recent structures are formed. The vector direction of prevailing stress during the post-Laramien time determines the direction of the folded structures. Fault surfaces of dinaric direction are created, along which rises the vertical or subvertical—reverse movement of the Mesozoic carbonate rock mass over Eocene flysch. There is no overthrust on a regional scale. Imbricated structures and reverse faults are frequent. Geoelectrical investigations and exploratory drilling proved that overlap of the north-eastern blocks took place along the surfaces of the discontinuity, in which the slope towards the northeast is always greater than 55°. The slope of reverse contact between flysch and carbonate blocks along the northeastern edge of Dabarsko Polje near the Vrijeka Spring is about 63° (Aranđelović, 1977); in the area of Zaloma, on three measuring profiles, it ranges between 57° and 70°; and in the Cerničko and Fatničko poljes, it ranges between 65° and 75°. Similar results were obtained from investigations near Gradina in the area of reverse discontinuity, at the village of Srđevići-Zalom-Kifino Selo. In the area of Mali Zaton, immediately near the sea coast, through drilling and geoelectric investigations, it was determined that overthrust surface to a depth of 65 m has a slope of 50°–60°. An overthrust line, with movement of hectometres, exists in the area of the High Karst Overthrust, only. By application of geophysical methods and investigation by drilling in the immediate hinterland of the Ombla Spring, it was determined that the slope of the contact between the carbonate of the Mesozoic complex and the Eocene flysch is very steep, to a depth of 60–80 m below the elevation of 0.00 m. The slope of the contact is 80°. Further into the hinterland, inclination is less steep—about 35°. This contact was followed a few hundred meters in the hinterland by investigation works— boreholes. An attempt to follow this contact further into the hinterland (1 to the 4 km) to confirm assumption about kilometers overthrusting did not give results. This assumption (very realistic) is based on the position of the contour of this same contact in the area of Dubrovacka Župa, where more kilometers in the overthrust zone were discovered by erosion. The slope of the overthrust contact in the Mlini area is less inclined, only 15°. Drilling and geoelectrical sounding proved that, in the area of Omble Spring, sediment of flysch formation builds a

1.4 Geological Characteristics

continuous hydrogeological barrier to a depth 250–300 m below elevaton zero. Also, drilling and geoelectric sounding confirmed that the depth of Tertiary sediment in Dabarsko Polje ranges between 200 and (over) 400 m, and in the Cerničko and Fatničko poljes it is over 130 m. A depth of 200 m was found in the narrow structure of Zalom. These depths are presented because of the exceptional role of flysch sediment in karst aquifer evolution in East Herzegovina. Pyrenean and Sava orogenesis phases were replaced by reactivation of transversal faults and formation of new ones, the creation and movement of huge tectonic blocks. As an example, along the Zubački fault, which is formed in an earlier phase by the rising of the eastern block (dominates vertical component of movements), sub-horizontal movement occurs and there is a relative shifting of the eastward block. In the deep and spacious depression that was formed by post-Eocene movements in the area of the massif of Trusina Mountain and Nevesinjsko Polje, the Prominaa series is deposited. Simultaneously with deposition of Promina conglomerate, continental conditions start that remain on most of the terrain to present day. Locally (sedimentary basins of Nevesinje and Gacko) during Neogene come up to the deposition of freshwater sediments with coal. Movement of tectonic blocks along the old faults continues even in the neotectonic period. The vertical component of movement dominates, so that the Neogene basins reach a difference in elevation of up to 1500 m. There are huge differences in elevation speed of certain individual tectonic units in the direction of the movement vector. While the central tectonic blocks of the region, especially the Orjen tectonic block, are distinguished by a trend of uplifting, simuntaneously, the coastal blocks and blocks at the delta of the Neretva River have a tendency of relative sinking. Downstream from the mouth of Bregava, the area of the Hutovsko-Svitavska depression and the delta of Neretva represent the most expressive recent accumulative spaces, due to their sinking. It was established, by drilling, that conglomerates on the surface of the terrain in Mostar (foundation of the well-known bridge) in the delta of the Neretva River are detected at a depth of about 175 m. A map of existing vertical movement of earth crusts (federal geodetic administration—Belgrade 1972) shows that the speed of sinking in the Neretva Delta is around 1 mm/year, and in the Orjena area about 4 mm/year. Translational movement of tectonic blocks is also rare. These movements are frequently followed by their rotation. Pliocene neotectonic activity represents a continuation of previous tectogenetic processes and can be considered a significant period in creation of neotectonic structure, which

19

represents an important component in karst aquifer evolution. At the end of the Pliocene epoch, magnitude of the karstification process increased, with simultaneous decrease in fluvial erosion intensity. Tectonic movements in the Pleistocene play an important role in the construction of recent geological structures and evolution of karst process. Carbonate masses are exposed to the strong effect of the Adriatic Sea and Neretva valley erosion bases, including numerous local bases of erosion— tectonic rift valleys—in which karst poljes are created. The homogeneity of carbonate masses is damaged. The carbonate massifs are disintegrated by a dense network of faults, and cracking of the faults enables intensive karstification. The well developed surface drainage network dies, and the privileged routes of underground flows increase, including development of karst aquifers. In the Riss-Würm period, 140,000–25,000 years ago, the level of the Adriatic Sea level fluctuated (according to Šegota, 1982) between 110 and 96 m below the current level. The Neretva Valley from the confluence of the Svitava-Hutovo Depression was, at the same time, cut to sea level. Obviously, the gradients of flows directed toward the erosion base levels were incomparably larger than the modern ones, and the depth and effect of karstification proportionately increased.

1.4.5

General Hydrogeological Characteristics

Karstification Dissolution, one component of the karstification process, has been studied in detail and described in numerous works and textbooks, so there is no need to repeat it here. The role of physical rock disintegration will be briefly presented here, including significant components of this process. This is very much noticeable and documented in the course of investigative work in this region. In carbonate rocks of the Dinarides in East Herzegovina, primary porosity has a negligible participation. Secondary porosity of tectonic origin is a large percentage of total porosity and represents the initial form for the development of tertiary porosity—dissolution porosity, the genesis of which is usually identified with the term karstification. Karstogenesis is a process which, with chemical and biological components, plays a significant role in the process of mechanical disintegration of a rocky mass. During the initial phase, chemical- biological components dominate; however, expanding the volume of channels and caverns plays a key role in physical disintegration. There are active base flows in karst aquifers in a dry period, with characteristics of free-surface laminar flows;

20

1

Natural Characteristics

Fig. 1.11 Physical component of karstification process. General presentation. Cross-section. A. Flow along karst channel with regular geometry. Fast-velocity water carries rock pieces. B. Turbulent flow after karst channel becomes narrower. C. Area with whirling water after

flow velocity decreases; mechanical erosion by rotation of whirling water transfers blocks and pieces in the form of pebbles and cobbles (Milanović, 2020)

however, during periods of saturation, the karst aquifer has characteristics of a hydraulic system under pressure. In this stage, the basic kinematic elements of karst underground flow should be explaned mainly by the laws of turbulent flow through rough conductors (Fig. 1.11). Turbulent flows, often under high pressure and in combination with neotectonic movements, demolish the rock mass around the karst conduits, provoking collapse of the blocks; size varies from the smallest fractions to cubic meters. In such conditions, the effect of physical disintegration of the rock to the smallest fraction is far more significant than corrosion (chemical dissolution) for expansion of karst channels and transport of bed load and float fractions. An example from an exploratory adit for HPP Dabar in Dabarsko Polje confirms this statement (Fig. 1.12). After blasting during adit excavation, pieces of rock filled a part of the channel below the level of the investigation adit.

After precipitation, a turbulent flow was formed through the channel which, through the process of evorsion (water mill), in a period of several days, turned pieces with sharp edges into completely rounded gravel. This turned approximately 25–30% of the rock into the smallest fraction that was transported by water towards the point of discharge. It would take hundreds, or maybe thousands, of years for that quantity of rock to be dissolved by corrosion. The zones of concentrated solution are created at fracture intersections and at the contact points of limestone with weaker or waterproof rocks. On the surface, there are numerous sinkholes, valleys or karst poljes with number of shafts, sinkholes and ponors. Within the rock mass, privileged zones of underground flows are created. The most important features in these zones are channels of high permeability. Intensity and direction of karstification development, in addition to large amounts of solvent (water), largely depends on

Fig. 1.12 Dabarsko Polje, investigation adit. (a) Carbonate blocks and rock piecesdisintegrated by blasting and mechanically eroded by whirling water (b) Cobbles and gravel created by the process of erosion

(attrition—wearing away of rocks by friction). Photo—Cobbles and gravel in cavern (Milanović, 1986)

1.4 Geological Characteristics

21

Fig. 1.13 Relationship between karstification and depth based on geological, hydrogeological and geophysical investigations. 1. Base of karstification, 2. Graph of karstification by depth, 3. Graph of electrical sounding, 4. Groundwater level, 5. Fluctuation ranges of groundwater level (Aranđelović, 1970)

the position of erosion bases. In addition to structural elements, erosional bases are the most significant drivers of the development of the karst aquifer evolution process. In the area of East Herzegovina karst processes are fully developed, and their hydrogeological characteristics are unique in comparison to, for example, the karst of Taurides, Hellenides, China or Yucatan. Depth karstification To determine the change in karstification intensity as a function of depth, the results of drilling and water permeability tests on over 140 deep boreholes in East Herzegovina (Milanović, 1979, Fig. 1.13) were analyzed. The boreholes were drilled in regions with elevations of 200 to 1000 m above the mean sea level. All were included in the analysis, with karst cavities (empty and filled) and high water permeability measured at 5 m sections. Very large permeability is accepted if permeability of the measured section is greater than the pump capacity used to pump water into the borehole. Large water permeability is declared when section absorbs a large quantity of water so that a pressure of 10 bars could not have been achieved. The sections that could sustain the pressure of 10 bars with determined permeability greater than 30 Lugeons belong in the next group. Karstification was determined at a total of 398 layers. Empty caverns were observed in 138 sections. Most of the empty caverns (57%) are located between 50–150 m depth. Figure 1.13 shows that karstification decreases with depth. The most karstified, and therefore the most water-permeable, zone is at a depth of 10–20 m. This is the so-called epikarst zone.

The geoelectrical sounding diagram is based on measurements at 300 of the same points over 5 years, at different underground water levels, including periods of minimum and maximum (Aranđelović, 1970) in an area of East Herzegovina. Based on these analyses, it was established that, in the area of Eastern Herzegovina, karstification (expressed across index karstification - ε) reduces with depth (H) by exponential law (Milanović, 1979): ε = 23:97
e 0:012 H At depths of 250 to 300 m, karstification is reduced to a minimum (this zone is the bases of karstification) but this does not mean that, in certain zones, especially along deep faults, there are no karst phenomena even at much greater depths. In deep boreholes in the immediate area of the analyzed region (in Nikšićka Župa, Montenegro), the presence of karstified formations was determined at a depth of 2236 m, i.e., 1600 m below sea level (B. Milovanović, 1964/ 65). Porosity The effective porosity in the Dinaric karst is mainly of secondary origin and consists of fissures, karst channels, caverns and porosity of the sediments that fill numerous caverns. Primary porosity of the vuggy type was not recorded. Localities with travertine are rare and without important hydrogeological influence. The data colected from numerous boreholes and the results of grouting works show that

22

effective porosity of the majority of rocky mass (>80%) is less than 0.5%. Relatively homogeneous karst is only the near-surface zone (the so-called epikarst). Hydrogeological singularities (channels and caverns) inside of relatively compact rock masses are pronounced at depth. An example is the head race tunnel for Reversible Power Plant (RPP) Čapljina, from the Hutovo area to the Svitava depression. The tunnel passes through an extremely karstified massif, with a highly developed network of underground streams that sink into the lowest part of Popovo Polje and flows towards the rim of the Svitava depression and the Neretva valley. The first 3600 m of the tunnel pass through a compact rock mass with rare cracks and without the slightest traces of karstification, that is, with estimated rock porosity 3%). Determination of underground flow directions In order to define the direction and velocity of groundwater flow in the karst area, a large number of surveys were carried out in East Herzegovina using tracers. The first attempt was made in 1880, when 200 kg of pouderise coal was thrown into the ponor (swallow hole) beneath corn mill in the Pridvorci branch of the Trebišnjica River near Trebinje, without success. Tracing was repeated with chaff, also without results. An experiment with 3 kg of Na-fluorescein, near Dražin do also failed (Gavazzi, 1902). For the next experiment with Na-fluorescein (Pridvorci, 1916), Absolon believes that the attempt finished without success because of inexperienced people that organized tracer test. The first successful tracer works were the tracer test of the ponors of Kikovac and Fetahagića shaft in Trebinja (Lazić, 1926); the Doljašnica Ponor in Popovo Polje (1926) and ponor near Branilović in the Small Gatačko Polje (Srnčić, 1928). Na-fluorescein was used most often as tracer, but radioactive isotopes and lycopodium spores were also applied. In one case, the hydrobiological tracer method was applied. For the more than 130 tracer experiments applied in

1

Natural Characteristics

the area of East Herzegovina, over 6000 kg of Na-fluorescein was used. To define the position of the watershed between the Trebišnjica and Bregava catchment areas in Fatničko Polje, Na-fluorescein and 135 kg of lycopodium spores in five different colors were used. In order to determine the velocities and depths of underground flows in the area of the Hutovo Reservoir and in Nevesinjsko Polje, the radioactive isotopes Br-82, J-131, Cr-51, and Tritium (3 H) and the post-activated isotope Bromine were used. In order to avoid uncertain results, large amounts of dye were often used. For instance, in the Ponikava Ponor in Popovo Polje, 160 kg of Na-fluorescein (1969) was injected. For the Dobreljska Cave and Milino Prisoje ponors in Gatačko Polje and for the Pasmica Ponor in Fatničko Polje, 150 kg of dye per each was used. For dye tracing in the Konac Ponor in Ljubinjsko Polje, 136 kg of Na-flourescein was used. Apart from those mentioned, in the case of 21 tracer tests, an amount of dye ranging between 90 and 117 kg was used. In some cases, the sampling setup for only one tracer test included up to 43 observation points, sometimes at distance of more than 30 km from the ponor in which was injected dye. The results of more significant tracer tests are given in Table 1.6. Since, in the majority of cases, appearance of labeled waves has been registered on a number of springs, only the most significant links are shown. The results of a large number of so-called local tests are not shown in this table. The velocity of the underground flows Numerous tracer tests have established that the fictitious velocity of underground flows varies between 0.5 and 55.2 cm/s. The underground flows of East Herzegovina are well known at high velocity. The highest velocity was measured in periods when the karst aquifer was fully saturated. A dye test in the Biograd Ponor in Nevesinjsko Polje, at high water level, showed fictitious velocity of the underground flow was 33.67 cm/s. The straight line distance between the Biograd swallow hole and Bunica spring is 20 km, a height difference of 760 m. Large flow velocity is registered in the huge aquifer of Trebišnjica Springs: – Srđevići (Gatačko Polje)—Trebišnjica Springs (Bileća Springs), 33.6 km—velocity 7.53 cm/s. – Jasovica Ponor (Cerničko Polje)—Trebišnjica Springs, 25.6 km—8.15 cm/s. – Ključki Ponor (Cerničko Polje)—Obod temporary spring, 14 km—11.2 cm/s.

1.4 Geological Characteristics

23

Table 1.6 Tracer tests results, basic data

No. 1 2

Location of dye injection. Level (m a.s.l) Babića spring- Zalomka. 895 Biograd ponor- Nevesinje799

3

Bobotovo cemetery 970

4

BravenikZupci 800 Brljuške Zalomka river 885 Budoši 487 Bitomišlje Češljari Swallow hole “C” Fatn.p.469

5 6 7 8 9 10 11 12 13 14

15 16 17 18 19

Crnulja Pop P. 228 Dobreljska peć Gacko Polje 880 Doljašnica Pop.P. 229 Doljašnica Pop.P. 229 Doljašnica Pop.P. 229 (92 kg) Estavella No. 4, Fatničko Polje 470

Geljov bridge Mokro p. 273 Gradina, Gatačko Polje 930 Gradina, Trebinje, 272 Jasovica, Cerničko P. 810 Kaluđerov Ponor. Pop. P.250

25

Ključki Ponor, Cerni.P. 818 Kočela, r. Trebišnjica, 262 Krupac, Trusina 1070 Kutske jame, Dabarsko P. 472 Lisac, Popovo P 223 Lukovice, Gat. Nadinici, 955

26

Međine, Gradac 70

27

Mlinica, Lukavačko. 852

20 21 22 23 24

Date of test, sink capacity Q(m3/s) 26.5.1973 5.1.1963 80 29.5.1964 0.15 3.12.1971. 0.03 17.5.1973 0.001 1.3.1975 0.012 1.2.1972 0.2 2.4.1964 Pasmica H=8m 7/3/1970 1.0 15.4.1963 0.075 5/5/1926 23.0 01.6.1960. 45.0 01.06.1962. Middle water level 17.12.1963 Pasmica ponor H = 8.09 m 8/16/1956 0.08 31.3.1975 0.1 22.9.1959 0.3 21.02.1964. 0.5 27.4.1970. 29.11.1961. 28.02.1972. ≈1 23.02.1972. 0.03 27.3.1956 9/5/1970 Dobri do H = 4.81 m 26.01.1972. 0.02 02.12.1970. 0.02 18.5.1961 0.07

Dye travel time (h) 112 16

Place of dye appearance. Elevation (m a.s.l) Ovčiji brod 838 Bunica spring 37

Distance (km) 5.70 20.0

Fictitious. speed cm/s 1.4 33.67

846

Piva spring 604

16.4

0.54

528

Konavoska Ljuta 90 Ovčiji brod 838 Stara mlinica 310 Janska (spring), Zagorje-Slano

10.0

0.53

4.8

1.72

3.2

1,3

Vel. Suhavić Trebišnjica spring. 325 Ljubanovo vrelo, Svitava, +3 Piva spring 604 Svitava +3 Svitava +3 Crni vir +3 Svitava, Derane Bistrine

22.4 17.8 12.4

7.15 8.24 3.54

18.1

1.19

11.7

7.7

11.7 18.3 11.7; 14 17.0 22.2 24.3 18.0 20.7 16.5

8.06 8.03

4.60 1.74 1.59 1.00 2.08

21.0 21.4 18.0

8.97 7.72 2.85

25.6 19.8 14.6

8.15 6,11 0.66

14.0 25.6 11.3

11.27 12.59 1.89

19.3

4.00

18.3 20.35 20.35 9.10 20.50

4.27 3.93 3.93 5.36 1.3

8.90

2.19

5.00

1.48

77 68 302 87 and 60 97 423 42 42 63

134 388 314 577 220 95 175 87 90 614 34 56 166 134

V. Suhavić, 195 Bitunja, 130 Treb. Spring. 325 Čepelica, 324 Ombla, Dubrovnik +2.5 Obod, Fatničko polje 476Baba jama Ombla spring, Dubrovnik +2.5 Trebišnjica spring. 325 Obod, 476 Glušci, Neretva +1.5 Obod Fatničko polje 476 Treb.spr.325 Ombla, Dubrovnik +2.5 Bunica 37

119 144 43 180 441

V. Suhavić, 195 Bitunja, 130

113

Mlinište, Neretva +2 Vrijeka and Sušica 475

94

Svitava, +3 Doljani, Ner. +2 Obod and Baba, Fatničko p. 476

0.98

(continued)

24

1

Natural Characteristics

Table 1.6 (continued)

No. 28

29 30 31 32 33 34

35 36 37 38 39 40 41

42

16.90 15.70 15.70

7.79 10.60 0.58

Trebišnjica spr., 325 m a.s.l. Čepelica, 324 Morašina (Ston), Bistrina, Budima, Janska, ± 0.0

15.80 18.20

13,10 13.48

92

Glušci, Neretva 2.5 m.a.sl.

16.00

4.82

232

Mislina, Ner. +2 Bili vir, Ner. +2

137

2.4 5.0 3.2

69 61 69

Ombla, Dubrovnik. 2.5 a.s.l. Ombla, Dubr. 2.5 Zavrelje, 100 m asl Ovčiji brod, 838

20.00 16.00 16.25 16.25 12.70 4.85

6.45 5.78 1.94

112

Zavrjele, Mlini 100

4.90

1.22

330

Vilina cave, Cernica 835

8.25

0.64

829

Trebišnjica spr. 325

33.65

1.13

124

Trebišnjica spring. 325 Obod, Fat. p. 476 V. Suhavić, 195 Bitunja, 130

33.65 19.40

7.53 5.73

10.40 12.20 4.85 6.20 15.40 24.60 11.00

1.8 1.9 0.95 0.91 0.88 6.7 4.7

16.00 18.00 27.10 10.70

12.80 6.0 11.0 3.15

27.02.1958. H = 9.22 m 23.03.1962. Dobri do H = 19.20 m 16.02.1969. 3.00 20.02.1962. 3.00 29.7.1956 0.52 28.3.1960 H = 1.25

33 37 48

Ponivka, Pop.P. 207 Ponikva, Pop. P. 207 Pridvorci, Treb. 273 Pridvorci, Treb. 273 Prisoje, Rilja 890 Slivnica, 410 Srđevići Gatačko Polje 940 Srđevići, Gat. P. 940

Slato Polje Mlinica 1000

46

Šuković Ponor, Cerničko Polje. 810 Trap, Mokro P. 275 Šabanov ponor Small Gatačko. Polje 924

52

1.1

75

45

51

1.40

25.02.1952. 0.5 9/9/1955 0.03 15.11.1955 Left = 0.12 right = 0.6 14.5.1955

Strupići, Dab. Polje, ≈500

50

6.70

Poljice, mill Popovo P. 244 Parež, Mruše 306 Ponikva, Dabar 471 Ponikva, Dabar 471 Pasmica Fat.P. 462 Provalija, P.P. (second test) 225 (105 kg)

44

49

18.00

Dye travel time (h) 257

Srđevići, Gatačko Polje 940

48

Fictitious. speed cm/s

Date of test, sink capacity Q(m3/s) 22.4.1969 0.3

43

47

Distance (km)

Location of dye injection. Level (m a.s.l) Bandera Mill Popovo Polje 238

Trnje, MokroP. 270 Velja Međa, Popovo Polje, 232 Vratlo, Vala 295 Zlatac, Nevesinjsko P. 828

21. 5, in 1974 0.10 3.12.1972. 0.01 23.7.1956 0.2 31.8.1958 1.0 19.10.1964 60 26.11.1972. 0.01 5/27/1961 0.02 26.3.1965 0.05 02.02.1972. 0.02 22.11.1962 H = 3.40 m 25.02.1957.

34 78 70 804

135 205 486 102

94

Place of dye appearance. Elevation (m a.s.l) Londža, Svitava. +3 Janska vrulja -10 Ombla, Dubrovnik +2.5 Oko spring upstream from Grančarevo, 299 V. Suhavić, 195 Bitunja, 130 Bitunja, 130

Zovidolka ponor near mill. 845 and Brusac, 841 Obod, 476 Trebišnjica spr. 325 Plat 1, 0.00 Robinson 1.00 Obod, 476 PB-1, 490 Treb springs 325 Robinson 1.00

22.4.1969 0.30

Derane., Londža +4, Janska, submarine spring

14.80 17.10

01.02.1973. 0.20 28. 3. in 1965 middle water level

Janska, 0.00

10.7

0.9

Buna, 37

21

4.40 (continued)

1.4 Geological Characteristics

25

Table 1.6 (continued)

No. 53 54

55 56 57

Location of dye injection. Level (m a.s.l) Ždrebanik Zalomka 835 Ždrebanik, Zalomka 835 Žira, Popovo P. 227 ŽdrijeloNeves. 825 Ždrijelovići, Ljubomir, 500

Ž-1, Žiljevo, Neves. P, 866

61

BR-1, Bregava 98

62

O-6, borehole. Ombla, 275

63

Ćetanuša, Zovidolka, 836

64

Ljeskovik Zalomka, 824

65

Moraj Luke, Zalomka, 909.

66

Kozjar, Gacko, Dobro P. 948

67

Milino prisoje, Nadanići 949

68

Obod Fatničko Polje, 476

1962

69

G. Zijemlje, Hansko Polje around 850 Crni kuk, Zalomka River

14.10.1975

Borehole B-2 Well B-4583.84 m a.s.l.

75

Skrobotno M-4407.90 m a.s.l.

76

Turčinovac GatačkoPolje, 928 m a.s.l.

77

Cavern in the tunnel for PP Dubr. 0 + 216

18.50

5.82

16.50

6.07

Tučevac, Trebinje 266 V. Suhavić, 195 Bitunja, 130 Treb. spring 325

12.05

10.46 9.08 6.81

Popovo polje Strujići, Meginja?

21.70 24.00 18.50 7.85

191

Buna spring 37

21.60

3.14

571

Derane, Drijen +4 Ombla spring +2.5 Buna spring 37

15.90

0.77

4.2

1.4

27

4.5

Buna spring 37

25.5

2.7

Zalomka, Rilja Ovčiji brod Zalomka, Luke

2.15 5.95 2.5 1.8

3.15 1.82 2.73 1.23

1.2 17.9 45.5 18.2 18.4 18.3

2.47 1.1 2.22

75

60

73 74

Bili vir, Neretva +1.5 Buna spring 37

4.12.1961. 0.23 9/11/1960 0.50 20.11.1957 0.004

Konac, Ljubinje 408

72

3.0

88

59

Estavella “Gorica” 280 m a.s.l. Borehole B-3

27.20

7/4/1970

Estavella near Vel.pećina Fatn. Polje.472

71

Fictitious. speed cm/s 3.94

Dye travel time (h)

58

70

Distance (km) 27.20

Date of test, sink capacity Q(m3/s) 01.4.1961 0.04 8/10/1969 0.003

22.12.1960. 0.5 3.3. in 1964 0.003 11.8.1975 0.0035 7/3/1986 pumped 5 m 3 water 18.5.1979 0.020 20.10.1988. 0.010 17.01.1978. 0.005 pumped up 5/17/1976 0.015 28.4.1972 0.050

7/5/1986 (30 kg dye) 26.3.1961 33 kg dye 04.02.1962. 0.075 01.02.1958. 15.05.1961. 43 kg dye 04/07/1961. 34 kg dye 22.11.1962 H = 340

01.07.1963. 1.5

252

32 66 68 97 654??

72

Place of dye appearance. Elevation (m a.s.l) Buna 37 Buna spring 37

Jezerina, Nadanici Jezerina, Nadini. Zovidolka Buna spring Dejan’s cave. Nikšić spring Oko

11/12 May 1968

120 384 66 Obod 68 Trebiš. springs 360 A well 312 Plat

0.33

Buna, Potoci, Livčina (Mostar Bijelo Polje) RB 1, RB-5, RA-3, RA-1, K-1 upstream of Rilja Oko Rasovac, Ombla, Zavrelje, Robinson Old Mill, M-2

5.5 17.3 7.25

Old mill Kopjela, Hercegov. jama

8.1 5.5

Kopjela, Hercegov. jama 327 m a.s.l. Obod, Baba, PB1, Trebišnjica spring

3.25

Well Police, Plattunnel No. II

16, 18, 27 17 (continued)

26

1

Natural Characteristics

Table 1.6 (continued)

No. 78

Location of dye injection. Level (m a.s.l) Estav. Gradina, 400 m upstream from Trebinje.

Date of test, sink capacity Q(m3/s) 22.9.1959 0.3

Dye travel time (h) 175 Ombla

Place of dye appearance. Elevation (m a.s.l) Ombla, Oko in Zasad, Tučevac, Dražin do

Distance (km)

Fictitious. speed cm/s

Note: The results of tracer tests inside the Bileća Reservoir area are given in Sect. 4.4.4

– Ključki Ponor (Cerničko Polje)—Trebišnjica Springs, 25.6 km—12.6 cm/s. – Pasmica Ponor (Fatničko Polje)—Trebišnjica Springs, 15.8 km—velocity 13.1 cm/s. Huge fictitious velocities are registered in others aquifers of East Herzegovina, by tracer tests of the following ponors (swallow holes): – Ponor zone Ždrijelovići (Ljubomirsko Polje)—Tučevac temporary spring (Trebinje), distance 12 km, velocity— 10.6 cm/s. – Ponikva Ponor (Dabarsko Polje)—Bitunja Spring, 16.9 km—7.97 cm/s. – Pridvorci Mill (Trebinje)—Ombla, 16.2 km—6.5 cm/s. – Doljašnica Ponor—Crni Vir, 18.3 km—8.3 cm/s. – Ponor Provalija (Popovo Polje)—submarine spring Bistrina, 16.6 km—6.4 cm/s. The highest velocity of the underground flows in East Herzegovina was determined to be between the Ponikva Ponor in Popovo and the boreholes in the Hutovo area, a distance of 1.5 km (velocity 55 cm/s) and at a distance of 4.3 km (33.3 cm/s). All the examples mentioned refer to the wet period of the year, that is, to the period when karst aquifers are well saturated. In the dry period, underground flows are considerably slowed down and take place only in the base flow zone. In those conditions, some of the above-mentioned flows are moved by next fictitious velocity: – Srđevići Ponor (Gatačko Polje)—Trebišnjica, Springs, velocity 1.13 cm/s. – Ponikva Ponor (Dabarsko Polje)—Bitunja spring, velocity 0.58 cm/s – Pridvorci (Trebinje)—Ombla, velocity 3.2 cm/s During the tracer test of the Biograd Ponor in Nevesinjsko Polje, 2 days before it dried up and sinking stopped, the labeled wave remained in numerous siphons of the main channel throughout the dry period of year. After the rainy period started, the labeled water apears in the Bunica Spring. Fluctuation of underground water level The level of aquifer water in the dry period is at a great depth, excluding the coastal area, where groundwater level

corresponds with sea level. In the continental parts, at higher altitudes, during the dry period it descends to great depths. These are usually depths greater than 100 m, but there are also frequent zones where the water level drops to 300–400 m below the terrain surface. An extensive piezometer network has been established in the territory of East Herzegovina, primarily for the purposes of designing and construction of the Trebišnjica Hydrosystem. For measuring fluctuation of groundwater level, over 400 boreholes were drilled and were equipped mostly with piezometric constructions. Their depths are from 20 m to 530 m. With the formation of piezometric networks in the middle of the last century, some piezometers have been observed continuously for more than 50 years. The established regime of observation was twice a week, but measurements were performed daily as needed and were equipped with automatic devices that enabled measurements every hour. The deepest borehole of 530 m was drilled at Dobri do, on the edge of the end of Popovo Polje, to determine the depth of the dolomite core of the anticlinal structure between the lowest part of Popovo Polje and the Adriatic Sea. One borehole was drilled to level, at an elevation of about 400 m, into the right bank of the Bileća Reservoir. In the locations with possible independent aquifers, double piezometers were embedded. This type of piezometer is often installed in Popovo Polje, to separately monitor water fluctuation in the alluvial deposit (shallow piezometer) and in carbonate karstified rock masses under alluvial deposits (deeper piezometer). The piezometers are concentrated in the zones that were of interest for the main structure design: the site area of the Grančarevo Dam; the right bank of the Bileća Reservoir; the region of Fatničko Polje; the tunnel trace of Fatnica— Bileća, Zalomka River Valley; Nevesinjsko Polje; Popovo Polje, including the catchment area of Ombla Spring; and the Hutovo Reservoir area. A large number of piezometric boreholes were drilled in the area of the Gorica dam site, the Gatačko Polje, Cerničko Polje, and in the area of Reversible Power Plant (RPP) Čapljina. A large number of deep boreholes were drilled in the immediate area but also in the wider hinterland of Ombla Spring, four of them in the area of Zavrelje Spring. These boreholes were drilled during investigations for underground HPP (Hydro Power Plant) Ombla.

1.4 Geological Characteristics

27

Fig. 1.14 Groundwater fluctuation graph in piezometric boreholes in the hinterland of Ombla Spring (Milanović, 1977)

Analysis of ground water level (GWL) data for the 140 boreholes established that, for some boreholes (at the perimeter of submerged poljes), the water level rises to the polje surface but also, in some boreholes, it remains at a depth greater than 200 m. In the dry period, the karst aquifer levels in a large number of localities are at great depth. In 85.1% of cases, the minimum is at a depth greater than 60 m and, of that, 63.7% of piezometer GWL data are measured at depths greater than 100 m. In 24.4% of cases, the minimum GWL was measured at depths of 200 m. Amplitudes of GWL fluctuation are different, from a few meters up to 300 or more meters. Analyzed data shows that the most common amplitude (59.2%) is between 20 and 80 m, while in 16.6% of cases, the recorded amplitudes are higher than 100 m. Large dimensions of karst channels, their mutual connection, large gradients and extensive infiltration capacity of the surface zone allow very fast filling and emptying of karst aquifers. Due to relatively small total porosity and extraordinary transmisibility, the ground water fluctuation is very fast and with huge amplitudes. Aquifers with more significant precipitation (more than 30 mm/24 h), in winter time, react after a few hours. Hydrograms are significantly different for wet and dry periods of the year.

A typical example of GWL fluctuation for East Herzegovina is given in Fig. 1.14. The diagram shows fluctuation in the aquifer of the Omble Spring. A similar fluctuation regime is registered in most piezometers of this region. In boreholes O-3 and O-10, in the hinterland of Ombla, amplitudes of 198 m were measured. In piezometric borehole O-9, which is located at distance of 1400 m from the spring, GWL fluctuation is between 5 m and 161 m above mean sea level, i.e., 156 m. In four more piezometers in this area, there are large amplitudes: O-2 = 166 m, O-4 = 158 m, O-6 = 158 and O-8 = 152 m. In both cases (GWL rising or decreasing), it occurs very fast. An example of fluctuation in O-10 is indicative. It is located in a zone where both structural and geoelectric analysis indicated deep and intensive karstification. It is drilled to 83 m below zero, and it is 1020 m away from the Omble Spring. The level in this piezometer varies from 35 to 233 m above sea level. The maximum measured daily rise of GWL is 99 m. Reactions of this aquifer to precipitation are very fast (Fig. 1.15). Under unsaturated conditions of aeration zones (after a long dry period) to hourly precipitation above 20 mm, GWL reacts after 2–4 h. The largest amplitudes recorded are in Nevesinjsko Polje, in the so-called Žiljevo carbonate ridge. Amplitudes measured in four piezometers in this area range from 281 to 320 m. These are the largest amplitudes known so far in the

28

1

Natural Characteristics

Fig. 1.15 Relationship between precipitation, groundwater fluctuation in piezometers O-6, O-8 and O-9 and Ombla Spring discharge (Q) (Milanović, 2006)

dinaric region. In a recession period, GWL decreased 312 m for 183 days, which is an unusually long period for karst (Fig. 1.16). This is explained by the good retardation characteristics of the Promina formation, which deposited karstified limestone in a huge paleodepression. The most significant hydrogeological area in the catchment of the Trebišnjica River is the Plana area. In piezometric borehole PB-1, located in the Plana area, the maximum recorded amplitude is 129 m. In this case, the level changes both in the period of growth and in the period of drawdown are very fast. Fluctuations of GWL greater than 100 m were also recorded under the bottom of Popovo Polje in the area of the Hutovo Reservoir. In this case, maximum levels also remain under the terrain surface. One of the very significant conclusions from analysis of a great number of piezometers is that relying on underground water data from one borehole, only in karst, is very risky. As an example, we list a few boreholes drilled in the areas with huge and active karst channels; however, rock mass along the boreholes was absolutely compact and watertight: the borehole drilled in the immediate areas of the Jasovica Ponor

Fig. 1.16 Recession graph for boreholes F-3 in Nevesinjsko Polje (Milanović, 2006)

1.4 Geological Characteristics

(Cerničko Polje); the borehole inside the Vrijeka Spring zone (Dabarsko Polje); boreholes in the area of Svitava Springs; a number of very close boreholes from the investigation gallery inside the Ombla Spring; however, a karst channel with a flow capacity of more than 100 m3/s was not detected. Measurement of water permeability along the boreholes showed compact and impermeable rock, and the level of underground water in them is not the real GWL. For reliable conclusions, a larger number of investigation boreholes are required; however, increasing the number of boreholes does not absolutely eliminate risk. Flow regime As a consequence of different karst aquifer evolution processes, complex hydrogeological connections are established within the karst aquifers of East Herzegovina. The most expressive examples of these differences in connection can be stated as: – Direct relationship between the ponor (swallow hole) of Biograd and Bunica Spring. – Sinking in one ponor zone, and discharging in the large number of springs (ponor zone at Popovo Polje bottom near Hutovo village, and discharge in a number of springs along the Svitava depression and the Neretva Valley near Metković). – Sinking into a large number of mutually distant ponors and concentrated discharge in only one spring (sinking in a large number of swallw holes between Trebinje and Poljica along Popovo Polje, and concentrated discharging of all these water in the Ombla Spring; or sinking through the numerous ponors in Nevesinjsko Polje including seepage along the Zalomka and Zovidolka riverbeds, and discharge in one spring only—Buna Spring. – Bifurcation zones (water that sinks into one single ponor and flows in the direction of different watersheds). Exampleas include sinking water from Fatničko Polje flows towards the Trebišnjica and Bregava catchment areas; water from the Provalija Ponor in Popovo Polje flows toward the north in the direction of the Svitava depression and south toward the Adriatic Sea coast). – A combination of all the mentioned cases. In the dry period, when the levels are close to the minimum, flow takes place mainly in basic flow zones. All waters, including those accepted by hanging flows, gravitate towards the base flows. In that period, these flows rarely come under pressure. It is a period when the real gradients that would formally be the base topographical position (elevation difference

29

between swallow holes and springs) are not realized, because the sinking water is in the form of underground waterfalls and subvertical flows very quickly reach the current groundwater level at high depth. The GWL is hundreds and more meters under the sinking places at the surface (Srđevići, Pridvorci, Doljašnice, Ključki Ponor, Ponikva in Popovo Polje and others), or 700–800 m lower (Biograd, Ždrijelo, Zlatac, etc.). Only then are they accepted by the basic flow channel. However, then flows with free water face very small gradients, so the flows are slow. The final parts of these flows, in the immediate area of discharge, come under pressure in the majority of cases. During the period of precipitation and inflow of large amounts of water through ponors, the karst aquifer becomes saturated, and the base flow along its entire length comes under pressure. In these conditions, the flow is taking place according to the square root of resistance. Considering that most often these are unique hydraulic systems (without significant channel branching), flow depends upon the square root of piezometric differences. So far, from hydrogeological and hydraulic viewpoints, the best analysed karst aquifer is Ombla Spring. Except for the entrance (the main sinking zone along the Trebišnjica riverbed) and the exit (discharge of Ombla Spring), through numerous piezometric boreholes in the aquifer zone, data were collected which enable analysis of the hydraulic characteristics of this aquifer with adequate accuracy. Especially significant are investigations from 1971. After several months of dry periods, on 19.07.1971 the overflow on the Gorica Dam was opened for 24 h. The overflow increased from 22 to 78 m3/s (Fig. 1.17). The overflowing water wave flowed along the riverbed for approximately 4–5 km to the zone where intensive sinking begins—the zone around Pridvorci and Mostaći and downstream along the bed. The Ombla Spring is 16.5 km away from the ponor zone. Although it was a dry period, when the underground circulation was reduced to the area of the base flow, this wave, after t = 36 h, caused an increase in the discharge from Ombla (point B). This increase of Ombla discharge is evident on the hydrograph in Fig. 1.17. The time between maximum water wave on the Gorica Dam and maximum spring discharge was only 22 h. Tracer experiments have shown that it is not enough time for water to pass that distance. Under similar hydrological and hydrogeological conditions, the labeled wave takes 137 h to cover that path (16.5 km). Obviously, the increase in flow on the Ombla Spring occurred as a consequence of pressure propagation in the base flow in this karst aquifer. Relation of the discharge at the Ombla Spring and GWL fluctuation in the piezometers in the hinterland of the spring

30

1

1.5

Natural Characteristics

Geomorphological Characteristics

Dominant regional geomorphological forms in this area are: – cascading system of karst poljes from the level of Nevesinjsko and Gatačko poljes (800–900 m a.s.l.) to sea level – relics of before-karst fluvial drainage networks in the form of dry vallieys – large karst plains and – extremely karstified mountain massifs and numerous surface and underground karst forms – sinkholes – lapies – shafts and caves A more detailed display of karst poljes follows in the next chapter and other more important geomorphological forms will be mentioned.

1.5.1

Dry Valleys

Dry valleys are relics of the former fluvial drainage system in which, in recent conditions, there is no flow, even during a period of the highest rainfall. There are numerous such valleys in East Herzegovina. Among the more significant dry valleys are: Fig. 1.17 Simultaneous graphs of water injection into ponor zone in riverbed (dam overflow at Gorica Dam) and spring discharge (Milanović, 2018)

are very pronounced, which indicates a very good hydraulic connection within this karst system. This is confirmed by very high correlation coefficients between Ombla discharge and GWL fluctuation in piezometers O-6 and O-9 (Table 1.7). Here are just some examples that characterize underground flow in karst of East Herzegovina and Dubrovnik Littoral.

Table 1.7 Correlation coefficient between Ombla Spring discharge and GWL fluctuation in piezometric boreholes

O-6 • • •

O-9 • • •

– Krstac, from the Gatačko to Nikšićko Polje, with numerous ponors (Bobotovo cemetery, Dobra voda-Čarađe and others). – The valley between the Lukavačko and Nevesinjsko poljes which, in before-karst time, had a role as the former outflow from Lukavačko Polje and was a tributary of the Zalomka River. A part of the valley between Lukavačko Polje and the Jama Spring (Udbina) was created in flysch sediments and, in this section, the surface flow does not exist. The downstream part of the riverbed is cut into the Promina formation in conglomerates and the temporary flow of the Zovidolka River runs along them. Ombla • • •

Coef. correlation 0.9470 0.9472 0.9791 0.9549

1.5 Geomorphological Characteristics

– The dry valley between the Slato and Nevesinjsko poljes is also a former outflow from Slato Polje and the Zalomka tributary. The Radimlja valley (Dabrica), from Nevesinjsko Polje to the Bregava River, was part of the Zalomka flow and was very rich with water. Through development of the karstification process and underground connections in the direction of Buna Spring, this part of the flow lost its own function. – The part of the Bregava valley from Dabarsko Polje to the spring zone of the Bregava River was, before the ponors in the polje were created, the main drainage flow. Since waters of Dabarsko Polje now flowunderground towards the springs of Bregava, the section between the springs and polje is converted into a dry valley without flow, even in periods of extreme precipitation. – In a period of active surface flows, water of Ljubinjsko Polje catchment area flows toward Popovo Polje. Recently, it is a dry valley without flow, even in the case of extreme precipitation. – The dry valley of Hutovo—Kolojan—Glušci is the former surface drainage of Popovo Polje, towards the Neretva valley. Below this valley is created one of the most significant underground drainage systems for flood waters of Popovo Polje. – Certainly, one of the most striking dry valleys in this part of the Dinaric karst is Vala, between Zavala in Popovo Polje and the Slano settlement at the sea coast. It was likely the most important surface drainage of Popovo Polje (Fig. 1.18). Due to subduction of the Adriatic

31

microplate and rotation of the tectonic block between the head of the High Karst Overthrust and Popovo Polje, the possibility of further transport of water in the direction of the sea is disconnected. In times of full fluvial activities, this flow continued a couple of kilometers, through the bay of the Slano settlement. Erosion relicts of this flow still are visible one the Koločepski channel at sea bottom. – Relicts of the ancient Trebišnjica River which one are registred across Orjen Mountain confirm the existence of a fluvial network that drained water of the Trebišnjica catchment toward Boka Kotorska Bay. According to Marković (1973), relicts of ancient Trebišnjica flow were discovered in the area of Grahovsko and Dragaljsko poljes (Montenegro).

The bottoms of dry valleys are, as a rule, covered with series of sinkholes, ponors, shafts and caves. They are very important for reconstruction of the old river network and for analysis of the karst evolution process. It is described in more detail in the chapter about Bregava (Sect. 2.1.20).

1.5.2

Karst Plain

The Trebinje Forest and Lug, including the famous Kistanje karst plain, certainly makes one of the well-known karst plains (karst plateaus) in Dinarides. More broadly, the Trebinje Forest (Trebinjska Šuma) represents the initial part

Fig. 1.18 Dry valley Vala between Popovo Polje (Zavala) and the Adriatic Sea (Slano). 1. Sinkholes, 2. Direction of old drainage flow from Popovo Polje, 3. Trebišnjica River, 4. Alluvial deposits in Popovo Polje, 5. Adriatic Sea

32

1

Natural Characteristics

Fig. 1.19 Trebišnjica dry river bed at the karst plain of the Trebinje Forest 1969 (Photo by Milanović)

of Popovo Polje and is characterized by vast, large leveled limestone with numerous shallow sinkholes and an isolated residual hill, a hum. This morphological form is a residual hill of carbonate rock on a fairly level floor or bottom of the polje. The term “hum” is accepted as an international term in karstology. The total area of the Trebinje Forest and Lug is about 120 km2 (Fig. 1.19). A. Cholley and G. Chabot (1930) analyzed the genesis of Popovo Polje and the origin of the Trebinje Forest, using theirs theoretical setting on the hydrographic concentration in areas consisting of limestone, and Cvijić’s conception of alternation of normal processes with karst processes, which are again replaced by normal—fluvial processes in their final phase. These authors believed that the plains of the Trebinje Forest were created in the late phase of Popovo Polje genesis. A. Grund, in his works (1903–1910), also analyzed this plain and explained its origin by the constant uplift of the downstream part of Popovo Polje while this area was tectonically inactive. Accordingly, Trebišnjica had a long period of time to form this plain. The photo (Fig. 1.19) shows part of the Trebinje Forest with the Trebišnjica dry river bed. There is no doubt that, upon creation of the plain of the Trebinje Forest, large amounts of cold water from melting glaciers on Orjen Mountain played an important role. Small karst plains can be classified: Hrasno, Vranjska, Bijela Rudina, Meka Gruda and part of Dubrava. Dubrava represents a transitional morphological form, with plain and polje karst characteristics at an altitude of

150–350 m. The cultivable area of Dubrava is estimated at 63 km2. Upper Cretaceous and Paleogene limestones, as well as flysch sediments, form the Dubrave region. There are significant agricultural areas, but surface streams did not exist and groundwater levels are very deep. According to oral information (Milanović, 2004), a couple of exploratory wells were drilled in the area of Dubrava. From the two exploratory wells in Rotimlja, 100 m deep, one measured a capacity of 2 l/s at a depth of about 80 m. According to a short term pumping test from an investigation borehole in Bjelojevići, 160 m deep, the yield was 2 l/s, while the yield of the second borehole at the same locality (depth 60 m) was 0.25 l/s.

1.5.3

Sinkholes

Sinkholes are among the most significant and most common surface morphological forms in karst. They are very common in the karst of East Herzegovina. Some sinkholes occasionally flooded; however, duration was short. They are most often created in intersections of two or more faults along the fault zone. These are the places most susceptible to karstification, known as zones of concentration dissolution (Fig. 1.20). Sinkholes can also occur through roof cave-in in caverns and karst channels located at shallow depths below the land surface. This kind of sinkhole origin was investigated near the village of Grebci, north of Osojnik, between Đurkovica and Nova Đurkovica caves (Fig. 1.21).

1.5 Geomorphological Characteristics

33

Fig. 1.20 Sinkholes near Vukovići village in the hinterland of the Ombla Spring. 1. Deposits of a sinkhole bottom (terra rossa), 2. Karstified limestone, 3. Fault (Milanović, 1981)

On fairly level parts of terrain, sinkholes are more frequent but of a smaller scale, while on uneven (hilly) parts of the terrain, they are less frequent but of larger dimensions (larger diameter and deeper). Figure 1.22 shows distribution and size of sinkholes on the plain between Popovo Polje and the sea coast including the area of Trebinjska Šuma (Trebinje Forest). Very often, sinkholes are connected by faults that mark the routes of significant tectonised directions. So, the tectonic zone from the Plana area toward the Trebišnjica spring zone is marked by a series of sinkholes, some of which are over 100 m deep (Fig. 1.23). With a line of sinkholes, regional Zubci and Slivnica faults are marked. In addition to the karst poljes, the bottom of sinkholes represents rare arable areas in the Dinaric karst. In a number of cases on their rims, individual households and sometimes smaller villages are formed, as is the case with the sinkhole between Zupci plain and Konavali Polje (Fig. 1.24). Such sinkholes (valleys) including Rapti on the southern edge of Popovo Polje and a few large sinkholes between Cerovac and Stolac (Fig. 1.25).

1.5.4

Fig. 1.21 Formation of sinkhole by collapse of the roof. 1 and 2. Entrances of the explored caves, Đurkovica and New Đurkovica, 3. Part of the cave roof that caved in, dividing the karst channel into two sections, with a sinkhole between them (Milanović, 1979, from data by M. Malez, 1970)

More Significant Mountains

The dominant mountains of this region are Orjen (1893 m) towards Boka Kotorska, Bjelasnica (1395 m) along with the northern rim of Popovo Polje, Hrgud (1108 m) along with the canyon of Bregava River, Bjelasnica (1867 m) and Baba (1735 m) southeast of Gatačko Polje, Crvanj (1920 m) along with the northeastern edge of Nevesinjsko Polje, Velež (1967 m) between Nevesinjsko Polje and Neretva

34

1

Natural Characteristics

Fig. 1.22 Distribution of sinkholes between Popovo Polje and the sea coast (Milanović, 1977)

River, Leotar near Trebinje town (1244 m) and Žaba (954 m) near the Neretva valley. Every one of these massifs represents a specific and unique geomorphological unit abundant whole, with pronounced karst features. Orjen, specifically, is known as an area with the highest rainfall in Europe and also for the largest density of deep karst shafts (Fig. 1.5).

1.6

Karst Poljes

Karst poljes represent one of the most famous karst features of East Herzegovina.

Fig. 1.23 Sinkholes between the Plana area and Bileća town

The first detailed description of a number of these poljes (Dabarsko, Fatničko, Plana, Cernica and Gatačko poljes) was presented by Cvijić in the work “Karst polje of west Bosnia and Herzegovina” (1900). On several occasions, Cvijić studied Popovo Polje and presented his observations in “Old drainages of Popovo Polje and hydrographic zones in karst” (1950) and in Geomorphology II (1926). In this monography 16 cascading karst poljes are presented, distributed from a height of 1100 m a.s.l. to 60 m a.s.l. (Fig. 1.26). Figure 1.27 shows a cross-section from Gatačko Polje to Ombla Spring at the sea coast, with water flow in wet and dry

1.6 Karst Poljes

35

Fig. 1.24 Large sinkhole in the Zupci fault zone between Zupci plain and Konavli Polje, used for agriculture 2010 (Photo Milanović)

periods. The position of the Lastva anticline that divides the karst area into two separate hydrogeological units is also indicated. All investigations done up to now, and especially the long-term operations of the watertight Bileća Reservoir, prove that an underground connection between the karst aquifers situated upstream and downstream of this hydrogeological barrier is not possible. Four groups of poljes can be grouped by elevation: 1. The poljes with the lowest horizon are the Gradac Polje (86 m a.s.l.) and Konavli Polje (60 m a.s.l.). 2. Hypsometrically, the horizon of Popovo Polje (250–220 m above sea level) and Mokro Polje, with the somewhat higher Trebinjsko Polje (270 m a.s.l.) 3. Middle horizon—Bilećko (420 m a.s.l.), Dabarsko (470 m a.s.l.), Fatničko (462 m a.s.l.), Ljubinjsko (400–470 m a.s.l.) and Ljubomirsko polje (520 m a.s.l). 4. The poljes with the highest horizon are Slato (1080 m above sea level), Lukavačko (880 m above sea level), Nevesinjsko (870–800 m above sea level), Trusinsko (850–870 m above sea level) and Gatačko (950–936 m a.s.l.). The largest, in terms of area, is Nevesinjsko Polje at 170 km2 and the smallest is Slato Polje at 1.3 km2.

In all these poljes, during a period of precipitation, water accumulates, so according to hydrological regime, they can be declared temporary flooded poljes. The floods occur most often between October and April, but there are a lot of floods registered in this one period. In addition to those listed above, Cvijić (1900) includes the following in karst poljes of East Herzegovina: – Stolac Polje which is part of Vidovo Polje near the Radimlja River and Humačko near the Bregave River. – Plansko Polje, north of Plana, about 2 km long and 700 to 800 m wide, which represents the transition between uvala and polje. In natural conditions, Popovo Polje is always the first submerged and, in a period of drainage, has the last released floods. Figure 1.6 graphically displays flood duration of Fatničko, Dabarsko and Popovo poljes. The Trebišnjica River catchment area consists of a few karst aquifers that are mutually interconnected and function in different regimes as a consequence of different saturation, i.e., under different ground water levels. The impervious structure of the Lastva anticline prevents hydrogeological connection between aquifers of the northern poljes (Gatačko, Cerničko, Fatničko and Bilećko) with karst aquifers and poljes south from anticline: Popovo, Trebinjsko, Mokro,

36

1

Natural Characteristics

Fig. 1.25 Sinkhole between Cerovac village and Stolac town, used for agriculture 1972 (photo Milanović)

Ljubinjsko and Ljubomirsko. Waters of western poljes (Lukavačko and Dabarsko) in natural conditions belongs to the Bregava basin. Due to construction of the Trebišnjica Hydrosystem the natural water route is partially modified because a part of water that belongs to these poljes has to be re-routed into the Trebišnjica watershed. Nevesnjsko and Slato Polje that belongs to Zalomka catchment as well as the waters of the northern part of Nevesnjsko Polje including part of mountain massif Velež in natural conditions make separate hydrogeological/hydrological entities that belongs to the catchmet area of Buna and Bunica. Karst poljes north from the Lastva anticline represent very complex but unique hydrogeological/hydrological entity. The system of underground flows by which are connected this two poljes is displayed on the Fig. 1.28 in horizontal and vertical projection. The basic data for constructing this (simplified) model were based on the results of numerous tracer tests, observations of piezometric boreholes, measurement flows

and flood levels in the polje. All the waters of this complex system are controlled at two outputs—on the springs of the Trebišnjica River and the springs of the Bregava River. The Popovo, Trebinjsko and Mokro poljes are not included in this model. These poljes are situated south of the regional hydrogeological barrier, the Lastva anticline, which has prevented the development of karst aquifers towards the south, i.e., towards the absolute erosion base— sea level. Due to the impossibility of achieving continuity of underground filtration, the surface flow connection has been established by creating the Trebišnjica River canyon through the dolomitic anticline core. In this way, a unique geomorphological entity was formed, made up of these three poljes. Because of specific conditions of creation with dominant directions of inflow from the north, by surface flow (theTrebišnjica flow) and from the east (water that belongs to Orjen Mountain), the Mokro Polje has some specific hydrogeological-hydrological individuality in relation to the Trebinjsko and Popovo Poljes.

1.6 Karst Poljes

Fig. 1.26 Karst poljes of East Herzegovina and Dubrovnik Littoral. 1. Reservoir, 2. Karst Polje, 3. Alluvioum and swamp deposits, 4. Spring, 5. Ponor, 6. Submarine spring, 7. Large fault zone,

37

8. Underground connections, 9. Permanent river flow, 10. Temporary river flow, 11. General directions of underground flows (Milanović, 1979)

38

1

Natural Characteristics

Fig. 1.27 Cross-section Gatačko Polje—Adriatic Sea (Ombla). 1. Karst spring, 2. Ponor, 3. Direction of groundwater flow, 4. Eocene flysch (hydrogeological barrier), 5. Neogene sediments, 6. Permanent surface flow, 7. Temporary surface flow (Milanović, 1979)

More details about the model of the karst fields south of the Lastva anticline are given, displaying natural characteristics of certain fields (Sect. 2.1.10).

1.6.1

Popovo Polje

Popovo Polje is undoubtedly the most famous karst Polje in the world. All of the phenomena which characterize karst and the karstification process are developed in this polje. Because of this, Popovo Polje has been a subject of interest and research for numerous leading karstologists. Many theories about karst and karstification were formed using Popovo Polje as an example. It has been particularly investigated in detail for design and construction needs of the Čapljina Reversible Power Plant. Geological, hydrogeological, geomorphological and tectonic characteristics Popovo Polje is divided into the corrosion surface of the Trebinje Forest (Figs. 1.29 and 1.30) and Popovo Polje sensu stricto (downstream from Poljica—Fig. 1.31). The surface of the Trebinje Forest is a vast karst plain modeled in Turonian limestone, with interstratified dolomite zones of different thicknesses. The plain surface is characterized by the absence of surface cover and it is slightly tilted toward the northwest. On a stretch of approximately 20 km, from Duži (elevation 275 m) to Poljica (elevation 250 m), the slope of the surface is uniform. Along the northern rim of this plain section, Trebišnjica flow cuts 13 km of shallow canyon. Between Tuli and

Sedlari, Trebišnjica flow approaches on the left polje rim, and so it flows to the village of Ravno. Downstream from Poljica, the polje is covered with an alluvial cover (Figs. 1.31 and 1.32), with 1 to 2 m thick local occurrences of limestone on the surface. Total area of the polje is 68.4 km2. The agricultural area is 44.15 km2 of which 39.06 km2 is arable. The width of the polje varies between 1 and 3 km, the largest width being between Dračevo and Sedlari. Elevation of the Trebišnjica riverbed at Dražin do is 264.94 m and, close to the polje end, at Dobri do, the water gauge station is at 226.87 m a.s.l. Popovo Polje was formed exclusively in carbonate formations of the Mesozoic complex. A couple of narrow zones of Eocene limestone are discordantly inserted in Cretaceous limestone, which builds the northern polje rim, between Strujići and Hutovo villages. They are insignificant, from a hydrogeological perspective. The thickness of Cretaceous and Jurassic carbonate formations in this area is greater than 3000 m. Dolomites in the Zelenikovac area build the core anticlinal structures along the southern rim in the lowest part of the polje. The dolomites are represented also in a significant mass in the area of Zavala and along the Slivnica fault. The dolomite anticline structure of Zelenikovac (Fig. 4.35) along the southern part of the polje rim is particularly significant due to its role in directing the fluvial erosion, i.e., in the creation of the dry valley Hutovo—Doljani, as well as in the process of karstification, which forms one of the most significant zones of concentrated underground circulation.

1.6 Karst Poljes

39

Fig. 1.28 Hydrogeological model. (a) Surface and confirmed underground connections between karst poljes of East Herzegovina. 1. Large karst spring Qmax > 50 m3/s, 2. Spring Qmax > 20 m3/s, 3. Ponor, 4. Possible underground connection in both directions, 5. Estavelle, 6. Underground connection, 7. Permanent surface flow, 8. Temporary surface flow. (b) Vertical projection of important underground connections between karst poljes. P—precipitation, H-groundwater level in boreholes (Milanović, 1992)

Next to the role it played in the karstification process in formation of morphological properties, the fluvial process also played a significant role in creating the characteristics of the polje. This means, except the waters that cames from the north, as product of the Orjen glaciers melting, the large quantities of cold waters that filled Mokro Polje with fluvioglacial material flowed further towards the west, creating broad karst plate known as Trebinje Forest. The direction of geological structures and the direction of most poljes are approximately identical. In both cases, the dinaric strike of structures dominates, i.e., dip direction northwest-southeast, with the most common inclination

from 15° to 45° in a northeast direction. In some cases, layers are vertical (Dobromani area). The formation of a polje is predisposed by the faults of the Dinaric direction of extension. Some of these crushing zones were identified along the northern edge of the polje next to the middle part of the Trebišnjica flow. These structures are dissected by a dense network of fractures almost perpendicular on the strike of a structure, which had a special significance for the formation of hydrogeological characteristics of the polje itself and for the wider region also. An example is the dense network of faults in the Trebinje Forest area, between Hum and Duži villages

40

1

Natural Characteristics

Fig. 1.29 Area of Ljubomirsko Polje—Mokro Polje—Dubrovnik Littoral (Ombla—Konavli) (Milanović, 1980)

and the Trebišnjica River, from the Dražin do to Dobromani (Fig. 1.33). According to the dimensions of the transverse faults that cross Popovo Polje, the Slivnica fault stretches from the Duboka Ljuta Spring (Robinson) at the sea coast, via the Duži area to the village of Kočela, where it crosses the Trebišnjica riverbed and continues towards Begovića Kula. A large number of shafts, sinkholes and caves were registered in that area. Dense net of karst channels of high permeability

were formed in the underground with flows towards the Ombla Spring. Downstream from the Poljica to the Hutovo area, the basic rock mass (karstified limestone) is covered with alluvial cover (Fig. 1.31). The thickness of these deposits increases in the direction of the polje slope. In the beginning, between Poljica and Dračevo, the thickness of alluvial sediments is 2–3 m, and the basic rock (dolomite and limestone) in many places appears on the polje surface.

1.6 Karst Poljes

41

Fig. 1.30 Area of Trebinje Forest and Mokro Polje. 1. Limestone, 2. Dolomites, 3. Flysch, 4. Piezometric profiles across the Trebišnjica River, 5. Fault zones, 6. Large temporary spring, 7. Small temporary

spring, 8. Small permanent spring, 9. Shaft, 10. Cave, 11. Ponor, 12. Estavelle (Milanović, 1980)

In between the villages of Zavala and Ravno, the thickness of alluvial cover is about 10 m, and in the lowest part of the polje, downstream from the Ponikva Ponor, it reaches a thickness of 25 m. The composition of these sediments includes gravel, sand, conglomerate, loam, sandy loam, clayey loam and humus. Carbonate paleo-relief, over which alluvial sediments are deposited have all the properties of typical karst (lapies, sinkholes, ponors). In the upstream and central part of the polje, the gravel fraction predominates and, at lowest part of the polje, alluvial deposits consist of clay and sand. The entire mass of alluvial sediments in the area of Zavala—Ravno is rich with gravel content. On the riverbanks downstream from Ravno, the largest gravel masses have characteristics of cohesive weak conglomerate, dominated by carbonate cementation.

Loam, sandy loam, clay loam and humus in most of the poljes play the role of the roof over gravelly-sandy horizon. On the basis of geophysical data, it can be concluded that on contact of alluvial sediments with carbonate base rock, a small layer of clayey-sandy sediment exists, with a thickness of 1–3 m, but continuity of this layer is most likely questionable. Loam originates from terra rossa, created by the decomposition of limestone, that has been washed from the surrounding slopes. These sediments can be divided in three groups, based on clay content: 1. Clay loam with content of pure clay: 38–51% 2. Loam with content of clayey components: 11–26% 3. Sandy loam with clay content: 2–8%

42

1

Natural Characteristics

Fig. 1.31 Wide area of Popovo Polje and Dubrovnik Littoral. 1. Permanent spring Qmin>2 m3/ s, 2. Permanent spring10 m3/s, 4. Small permanent spring, 5. Small temporary spring, 6. Estavelle, 7. Ponor or shaft, 8. Cave, 9. Underground connection, 10. Temporary surface flow, 11. Submarines spring, 12 Karst Polje, 13. Limestone, 14. Dolomites, 15. Flysch. Standard geological notations were used for tectonics (Milanović, 1980)

Of the fault structures in this part of the polje, the most remarkable is the Trnčina fault that cuts Popovo Polje in the area of the ponors Provalija and Doljašnica. Natural construction material and bituminous rocks Mineralogical-petrographic analysis of 12 limestone samples taken from an open outcrop of thick-bedded limestone at Kočela, on the left bank of the Trebišnjica River, showed that it is limestone with uniform properties and quality. After polishing, the samples were characterized by a high gloss, and the presence of fossils gives them a beautiful appearance. This limestone has good physical and mechanical characteristics, so it can be used as decorative building material. The characteristics of light brown to white cretaceous limestone from near the road between Zavala and Slano

were examined in a laboratory in SR Serbia (1974). In the category ‘Opinion on rock mass quality’ it was pointed out that it is limestone with very good technical properties. It is characterized by very high pressure resistance, high bending resistance, very good resistance to wear, slight porosity and low water absorption. The effect of frost is stable. It can be used as a decoration stone for vertical cover of interior and exterior. It belongs to the category of very hard limestone, which is resistant to cutting. Bituminous limestone were registered in the area of Dobroman, between Ravno and Čvaljina (immediately above the railway tracks), in the area near Kolojanj, close to the road between Hutovo and Metković. Bitumen deposits were registered in some boreholes in the wider area of the village of Hutovo.

1.6 Karst Poljes

43

Fig. 1.32 Popovo Polje 1969 (Photo Milanović)

For the purposes of construction of the Čapljina RPP project, several localities were investigated as potential sites for gravel. An area with gravel upstream of the bridge in Ravno was investigated in detail. Geophysical surveys were carried out as week as investigative drilling. These investigations proved thathis deposit contains 514,425 m3 gravel. Ponors in Popovo Polje All waters that reach Popovo Polje are drained exclusively through underground karst channels, towards the lower erosion bases, namely the seacoast, the Neretva valley and the Svitavsko-Deranska depression. About 500 sinkholes and estavelles were registered in the polje (Fig. 1.31). The largest ponor is Doljašnica, with a maximum absorption capacity of about 55 m3/s (Fig. 1.34). Determination of exact maximum capacity is very difficult since the ponor is then submerged, and conditions for measurement practically do not exist. In 1926, the ponor was artificially connected with the Trebišnjica riverbed by canal. The goal was to make earlier drainage of floodwaters possible.

With large swallowing capacity are ponors Provalija and Crnulja with maximum of about 10 m3/s (Fig. 1.35). The maximum swallowing capacity of Ponikva Ponor (the ponor at the very end of the Trebišnjica flow) and Žira is from 3 to 5 m3/s. In natural conditions, it often happens that the opening of Ponikva is plugged by sediment and branches, transported by river flow and floodwater. During geological mapping and production of the inventory of ponors along Popovo Polje, a large number of these phenomena were recorded, whose swallowing capacity is estimated at 0.5–1.0 m3/s. Corn mills were built on a large number of these sinkholes. Most of them were destroyed by building a canal for Čapljina RPP or are abandoned. A few preserved mills, like those at Dobromani (Fig. 4.3) are out of order. Substratum beneath Quaternary sediments consists of karstified limestone-dolomite rock masses. Numerous old ponors, which are buried with alluvial sediments, are periodically activated and manifest on the surface in the form of the so-called alluvial swallow holes (ponors). Alluvial ponors are frequent occurrences downstream of Velja Međa. They are absent in the Zavala area. The largest alluvial ponors were

44

1

Natural Characteristics

Fig. 1.33 (a) Discontinuity net in the area of Trebinjska Šuma (b) Diagram of prevailing orientation of fractures (Milanović, 1977)

located a few hundred meters upstream from the Ponikva Ponor and in the western part of the polje, i.e., in the area of the Hutovo Reservoir. They most often have a funnel-like shape and can be of different sizes, from barely noticeable to very large, with a depth of up to 10 m and a diameter of the upper funnel rim of 15–20 m (Fig. 1.36). The thickness of clay-sand sediments which cover a real ponor opening in paleo-relief varies from the couple of meters to 50 m. During a flood, these ponors change their size, shape and position. Some of them become plugged and lose their swallowing function. Frequently in close vicinity are open new one or few more.

The reason for their genesis is mainly the process of suffusion. Figure 1.37 presents five possible stages of alluvial ponor genesis. But their formation can also be a consequence of destruction of the alluvial cover by pressurized air that is compressed in underground cavities during a period of sudden rise of groundwater level (Fig. 1.38). Estavelles In natural conditions, estavelles had great importance in Popovo Polje, from the aspect of flooding as well as from the aspect of drainage. The most important estavelle zones are located in a part of the polje between Dračevo and

1.6 Karst Poljes

45

Fig. 1.34 Doljašnica Ponor in Popovo Polje

Strujići. This area is characterized by large discharge and plays a significant role in the balance of the waters of Popovo Polje. In this area, 44 individual estavelles are registered and 33 localities with groups of 3–7 close estavelles. Some of them have the form of large shafts and caves, while the smallest ones are in the form of small suffusion depressions in the alluvial cover. They can reach a cumulative discharge of 70 m3/s. Some estavelles represent parts of large karst systems. At the surface, these estavelles are presented in the form of large shafts and caves of considerable size. Some of them, such as Meginja, Plitica and Kapuša, are partially speleologically investigated. The Plitica channel, after about 250 m, ends in a siphonal lake. There are two distinctly different groups of estavelles. In the case of Dračevo-Strujići estavelles, in natural conditions, discharging and swallowing regimes are equally distributed. In the case of estavelles along the Trebišnjica riverbed in the Poljice area and along the southern rim of polje between Poljica and Zavala, the sinking function dominates. A rare discharge of water, of short duration, occurs in extreme

hydrological situations (if daily precipitation in a wet period exceeds 100 mm). Temporary springs There are no permanent springs in Popovo Polje. The most important temporary springs belong to a group of hydrogeological phenomena—caves with water. In the winter period, after longer rainfall, large quantities of water flow out of these springs and, in the summer period, water is retained in the available siphonal lakes in the karst channels and caverns. In a period of long-term drought, these were the only sources of drinking water in these regions for people and animals. One of the most significant groups of these temporary springs is situated along the northern polje edge between Lug Plain and Dobromani. The other more significant group of these springs is located along with southern polje rim, in the wider area of Zavala. The most significant are Mareva Ljut (Pokrivenik) and Lukavac, below the entrance to the Vjetrenica cave, and Čvaušnik, near Čvaljina. This zone is interesting because

46

Fig. 1.35 Crnulja Ponor in Popovo Polje, 1970 (Photo Milanović)

1

Natural Characteristics

geological characteristics and certain hydrogeological indications make this the only area in Popovo Polje that justifies hydrogeological analysis and investigative work, in order to determine the possibility of underground exploitation for water supply (limited scale). Lukavac was investigated by M. Radovanović in 1924, 1925 and 1926 as part of researching the Vjetrenica cave. On the basis of observations of Lukavac and aneroid measurements of the height of the springs and lakes in Donja (Lower) Vjetrenica, as well as tracer tests, he concluded that they are not in mutual connection. However, during investigative pumping test that was organized by the Institute for the Utility and Protection of Karst Waters, Trebinje (1980), it was established that the spring of Lukavac has a direct connection with the water of Lower Vjetrenica. The pumping of water from the spring was followed by a simultaneous decrease in the water level in the underground lake of Lower Vjetrenica. With the cessation of pumping, the lowering of the water level stopped. After this research, Lukavac was eliminated as a potential water supply source. The Pokrivenik Spring is located below the village of Mareva Ljut, on the very edge of the polje. It has the shape of a cave, which is filled with water in a dry period. During 1980 (August and September), two exploratory pumping tests were carried out. The first prospecting pumping test lasted only 3 h. The second withdrawal test lasted from September 15 to 27. The capacity of the pump was 30–20 l/ s, and it achieved drawdown about 5 m. Due to backfilling of the channel by the sliding of local gravel, further pumping was not possible, and the experiment was interrupted.

Fig. 1.36 Alluvial ponors—the lower part of Popovo Polje, 1970 (Photo Milanović)

1.6 Karst Poljes

47

Fig. 1.37 Schematic presentation of the most important phases in subsidence-ponor formation at the alluvial bottom of Popovo Polje (Milanović, 1979)

Water samples for bacteriological analysis were taken three times, once in a period when water discharged and twice in steady state situation. The presence of bacteria that are not allowed in drinking water was determined in only one sample, taken in a dry period when the locals capture water directly from the unprotected spring. It should be kept in the mind that on a slope above the spring there is a hamlet, whose wastewater represents a constant source of potential pollution. The Čvaušnik Spring has not been specifically investigated or analyzed. In the winter period, discharge of this spring is greater than 100 l/s. Drainage from Popovo Polje in natural conditions In natural conditions, drainage from Popovo Polje occurs exclusively through numerous sinkholes and flow through underground karst channels towards the Adriatic Sea, the Neretva Valley and the Svitava-Derane area. Demarcation of these catchments in the polje area is extremely complicated. The boundaries of the water divides are variable in time and space and depend on the current ratio of surface and groundwater. In the bifurcation zone in the area of Velje

Međa, the waters of Popovo Polje flow towards the seacoast and, at the same time, towards the Svitava-Derane area. The ratio of water quantities flowing simultaneously in one or the other direction permanently changes and depends on the current level of underground water in that zone. This has been comfirmed by repeated tracer tests of ponors— Provalija, Doljašnica and Mlinica close to the village of Velja Međa village. By measuring the losses in the dry period, it was determined that total capacity of the ponors along the Trebišnjica riverbed, including ponors connected to the riverbed, exceeds 130 m3/s (see Sect. 2.1.11). The other ponors in Popovo Polje are located outside the riverbed, at higher elevation, and swallow water when the polje floods. When the depth of the flood water reaches 25 m, the outflow through the ponors is about 180 m3/s. At the time of maximum flood elevations and optimal conditions in a karst aquifer (sudden lowering of the GWL), the cumulative sinking capacity is about 250 m3/s. A diagram of cumulative swallowing capacity of the ponors along the Popovo Polje, according to data registered at a water gauge station in Dobri do, is given in Fig. 1.39.

Fig. 1.38 Formation scheme of subsidence ponors under the influence of pressurized air. 1. Flood water level, 2. Alluvial sediments, 3. Karstified carbonate rock, 4. Ground water level (Milanović, 2000)

48

1

Natural Characteristics

Fig. 1.39 Popovo (1972) and graph of cumulative sinking of ponors up to flood depth of 25 m (Photo Milanović)

Duration of floods in Popovo Polje is usually between 220 and 240 days, but it can last much longer. Floods lasting more than 300 days were registered in 1883, 1897, 1900 and 1915. In some cases, the flood water reached the Dobromani area. One of the largest floods in the period following was established at the hydrological station on 01.03.1941. On that day, maximum elevation of the registered floodwater was 260.76 m a.s.l., i.e., 33.94 m above the lowest part of the polje. About 1 billion cubic meters of water accumulated in the polje area. An area of over 7000 hectares was flooded. The floodwater level was registered in the canyon part of the Trebišnjica riverbed in the Dražin do area, close to the Trebinje urban area. Figure 1.40 presents average duration of the flood for 1924/25–1941/42 and 1945/46–1957/58. These graphs show that the polje was submerged, on average, for 7 months (November–May), and only slightly in June and July. In August, September and October it was not flooded, or very rarely. Depending on the ratio between surface and underground waters, Popovo Polje can be divided into three hydrologicalhydrogeological entities (Fig. 1.41). The lowest part of the polje—A—is practically surrounded on three sides by a close base of erosion. Since the difference between the polje and this base level is over 220 m, underground water circulation takes place under the influence of large gradients in the direction of the SvitavaDerane depressions, the Neretva valley, and from the area of Provalija Ponor toward the Adriatic Sea (submarine springs from the Budima to Bistrina, Fig. 1.42). This condition influenced formation of the underground drainage system,

with large drainage and transmission capacity. The capacity of drainage channels is considerably higher than the maximum capacity of all ponors located in this zone. Therefore, even during the highest flood levels, the groundwater level rises to near the polje surface but never rises above the polje level. This zone is characterized by ponors, the most important being Doljašnica, Provalija, Crnulja, Lisac and Ponikva at the polje level, and Žira and Kaluđerov Ponor on the polje bank. Between the sections from the Provalija Ponor and the very end of the polje, there is no underground flow connection with the seacoast. The reason for this is the Cretaceous dolomite in the anticline core which, in the area of Zelenikovac, makes the southwest rim of the polje play the role of hydrogeological barrier between polje and seacoast. Fluctuations of GWL beneath the lowest part of polje (the current area of the Hutovo Reservoir) are around 100 m. In the central part of the polje, which is marked B in Fig. 1.41, estavelles are the dominant hydrogeological feature. A dolomite zone between Popovo Polje and the seacoast, from Ravno and Zavala to Zaplanik in the Ombla hinterland, has a crucial role in its origin. This dolomite zone acts as a hydrogeological barrier to groundwater flows and prevented direct hydrogeological connection between the polje and the sea. This causes very fast rises of the water level in the polje area. A large inflow of groundwater (q1) and water from direct infiltration (q2) are much greater than the drainage capacity (q), and the aquifer’s water table rises. Since the upper aquifer surface dips in the direction of the absolute base of erosion, water emerges first to the surface along the perimeter of the polje, which is located further

1.6 Karst Poljes

49

Fig. 1.40 Flood level duration graphs in Popovo Polje for 1924/ 25–1941/42 and 1945/46–1957/ 58 (according to Energoinvest)

away from the base of erosion. Along this perimeter, estavelles start to function as springs. One part of this water emerges at the surface of the local base with the discharge (q3). The level released in that position is marked (1) on crosssection b′—b. Some estavelles may even begin to function before the regional groundwater level has been established. These estavelles are connected to channels in which hanged water courses can be formed. These flows, depending upon the maximum ground water level, can take place in openings located above the GWL or they can be absorbed by the aquifer. Part of the water from these estavelles is lost on the opposite side of the polje through the estavelles which, at that moment, function as ponors. During high precipitation, when the water level reaches position (2), these estavelles begin to

operate as springs by increasing the rate of flooding of the polje. Between the dolomite zone and the seacoast, occasionally part of the dynamic reserves of the aquifer can be derived from the discharge (q2) occuring within the immediate river basin. These waters feed temporary springs which are located closest to seacoast. Zone C in Fig. 1.41 covers the upstream part of the polje and part of the Trebinje Forest. It is characterized by temporary springs and ponors. The springs appear along the northern edge of the polje, and ponors are registered mostly within the riverbed or in the area surrounding it. With rising GWL, the springs are activated, and part of aquifer begins to drain out by flow (q3). The major portion of water circulates underground in the direction of bases of erosion with the

50

1

Natural Characteristics

Fig. 1.41 Schematic representation of the relationship between surface and groundwater in Popovo Polje. 1. River and marsh sediments, 2. Karst polje, 3. Dolomites, 4. Ponor, 5. Estavelle, 6. Temporary spring, 7. Permanent spring, 8. Direction of groundwater circulation, 9. Sinkhole and spring zone, 10. Riverbed of the Trebišnjica River, 11. Flood levels, 12. Hydrograph of piezometer level in the springestavelle zone, 13. Hydrograph of piezometer level in the ponorestavelle zones, 14. Flood level hydrograph, 15. Bottom of polje, 16. Part of hydrograph during extremely high GWL, 17. Springestavelle zones, 18. Ponorestavelle zone (Milanović, 1979)

flow (q1). Drainage capacity is regulated by the capacity (q) of channels that form the drainage network. The total discharge (Q) also depends on the rate of GWL fluctuation. The transmission capacities of these channels are such that ponors always function without interruption. Surface outflow from the polje is always oriented in the direction of the lowest part of the polje. Therefore, the part of polje marked C seldom becomes flooded. The specific relationship between underground and surface water flows in these three zones of Popovo Polje can be observed on the graphs in Fig. 1.41. In case A, the GWL never reaches the level of the polje, even during high floods. The flood occurs (point E on the level graph) under the influence of surface water which flows into this part of the polje.

The ratio of underground and flood waters in zone B is characteristic for the majority of karst poljes. Piezometric levels in the spring-estavelle area (the part in which the estavelles mainly function as springs) reach polje level— point E—very quickly after heavy rainfall. At the rim of this part of the polje, GWL rise high above polje level. On the graph, this is a solid line marked with the number 1. As a consequence of high piezometric lines and large gradient, there is discharge of the aquifer along this edge of the polje. Piezometer levels in the ponor-estavella zone (the zone where the estavellas work mostly as ponors) are below the polje level, so that part of the surface water is lost through the ponors. When inflow is larger than the capacity of the ponor (point F), a polje flood may occur. After cessation of precipitation, piezometric levels in a spring-estavelle zone decline

1.6 Karst Poljes

51

Fig. 1.42 Area of Popovo Polje—Svitava—River Neretva—Adriatic coast. 1. Limestone, 2. Dolomites, 3. Ponor Q > 3 m3/s, 4. Group of close spaced ponors, 5. Ponor, 6. Estavelle, 7. Submarine spring,

8. Permanent spring, 9. Temporary spring, 10. Established underground connection, 11. Flysch, 12. Fault, 13. Overthrust, 14. Established underground links (Milanović, 1971, modified 1980)

faster than the decrease of the flood level. The water level graph of this zone, which until then was higher than the flood level line, drops sharply, and it intersects the flood line at point G, shortly afterwards descending below the polje level. At that moment, inflow into the polje stops completely. Estavelles work like ponors. The phase of exclusive polje drainage ends (H) when the polje is totally empty. In extreme cases (dashed line, marked number 2), piezometric levels in the ponor-estavelle zone can reach the polje level and even rise above the flood level. Then, the ponors in this zone function as springs and are sometimes defined as estavelles. These are rare cases and last a short period of time. This occasionally happens with ponors of such capacity as

Srđevići in Gatačko Polje, Pasmica in Fatničko Polje or Ponikva in Dabarsko Polje. In zone C, level diagrams of GWL fluctuations in the spring zone (solid line) and level graph of fluctuation in piezometers in the ponor zone (dotted line) clearly differ. The piezometric level, i.e., the aquifer level issued in the ponor zone, behaves the same as the level issued in area A. It never reaches the polje level. The level issued in the hinterland of the spring zone (full line) behaves like a level in the spring-estavelle zone in the section of the polje marked B. Temporary springs become active in the period when the piezometric line in the hinterland reaches the polje level.

52

1

Natural Characteristics

Fig. 1.43 Panoramic view of Trebinje town and Trebinje Polje, 2019 (Photo Milanović)

1.6.2

Trebinjsko Polje

Morphologically, Trebinjsko and Mokro poljes make a geomorphological connected entity, with a total surface of about 12 km2 at elevations between 275 and 270 m a.s.l. The surface of arable land is 11.3 km2. Morphologically, hydrogeologically and hydrologically, Trebinjsko Polje belongs to the Trebinje urban area until the Gorica Dam. Trebinjsko Polje is partially morphologically separated from Mokro Polje with the Mali Hum (Small Hum) and Veliki Hum (Big Hum). North and west of Hum is Trebinjsko Polje, and in the southeast direction is Mokro Polje (Fig. 1.43). Unlike most karst poljes, the Trebinjsko Polje is hydrologically open in both upstream and downstream directions. In the downstream direction, it continues to the Trebinje Forest and Popovo Polje. These geomorphological karst entities are mutually connected by the valley through which it passes, toward Trebišnjica riverbed. Except for the Nevesinjsko Polje, this polje of East Herzegovina does not have a longer axis in the dinaric direction. The most significant river in East Herzegovina—the Trebišnjica River— flows through the Trebinjsko Polje. In natural conditions, Trebišnjica is permanent flow from the spring zone to the Trebinje area and, in the summer, it dries up downstream from Trebinje, between the areas of Mostaći and Dražin do. The polje is formed in thick-bedded to massive karstified limestones of the Upper Cretaceous (Turonian) age, over

which sandy-clayey sediments were deposited, with a thickness of 1–3 m (Fig. 1.44). Morphological modelling of the area of Trebinjsko, Mokro and Popovo poljes shows the existence of an ancient Trebišnjica flow in the period preceding the cutting of the Lastva anticline. It became the erosion base level for the waters of the surrounding mountain massifs for surface waters as well as for underground waters. Along the perimeters of these poljes are numerous springs. The water of these springs, together with the waters of Orjen glaciers, played a key role in the formation of these poljes. Permanent springs do not exist, but there is a large number of temporary springs, in the form of shafts with water, that were arranged for access to the siphon lakes in dry periods. They are registered in the Trebinje urban area. The most important temporary spring in Trebinjsko Polje is Tučevac Spring near Dražin Do, at the entrance of the Trebišnjica River in the canyon-like part of the bed. The maximum discharge of Tučevac is more than 20 m3/s. The most upstream part of the Trebinjsko Polje towards the Gorica suburb is characterized by temporary springs (mostly along the northern rim of the polje, with large maximum discharge). Ponors are predominantly situated along the southern rim. From the springs in Gorica to the Tučevac, there is a large number of springs, among which the following are important: Vrulja on Blace, Fetahagića well, Zasad Spring and Lušac Spring (Fig. 1.45). Discharge of each of these springs in the wet period of the year exceeds 5 m3/s.

1.6 Karst Poljes

53

Fig. 1.44 Hydrogeological map of Trebinjsko and Mokro Poljes

In the riverbed of Trebišnjica, downstream from Trebinje, several estavelles were registered. Downstream from the Gorica Dam, on the left bank there is a permanent but small spring—Studenac. The catchment areas of these springs encompass the wider area of Ljubomirsko Polje, including the sub-catchment of Brova and Zmijanc temporary flows. Estavelles, which are mostly active in sinking regime, are registered along the beds of Lušac creek and along the Pridvorci flow branch. The springs are mostly located on the perimeter of the polje or

they are situated a few meters above the polje level (springs in Gorica and Zasad). After construction of the Gorica Dam, the flow regime of Lušac temporary spring changed into a permanent spring because part of the water that sinks into the Gorica estavelle, situated upstream of the dam’s inside reservoir, discharges from Lušac and then flow capacity depends on reservoir level. A large number of ponors are registered along the Trebišnjica riverbed and in the Pridvorci river-branch. Swallowing capacity of the largest single ponor in the

54

1

Natural Characteristics

Fig. 1.45 Trebinje area. Temporary springs along the northern border. (a) Lušac Spring (b) Spring in Gorica (c) Fetahagića natural well (d) Spring in Zasad

Pridvorci river-branch is between 0.5 and 1.0 m3/s. The mill is constructed at that ponor (Fig. 1.46). The first successful tracer test of the ponors in Trebinjsko Polje was done in 1926 (A. Lazić and S. Milojević). Dye was injected into Kikovac and Fetahagića ponors. A tracer test of Pridvorci Ponor was done in 1956 and later in1960. During the small water flow (1956) a connection with Ombla Spring was established at the seacoast, and during the large flow (1960), when the water level above the ponor opening was 1.25 m, connections were established with Ombla and with Zavrelje Springs in Mlini settlement at the seacoast. The waters of Trebinjsko Polje flows predominantly as surface flow (Trebišnjica River), but a considerable portion sinks and flows towards the sea coast as underground flow. Like all karst poljes, the Trebinjsko Polje is subject to flooding. That’s why all old houses are built on the slope above the flood line. In some cases, the urban part of Trebinje was also flooded. Before the construction of the Grančarevo Dam, the largest floods were registered on October 23, 1939, with an elevation of 275.24 m, and on 19.12.1952 with an elevation of 274.79 m. The flood that occurred in December 1903 is well known, with an elevation of 274.55 m

(Fig. 1.47). During that flood, the Dobromani gauge station registered one of the largest recorded flows of the Trebišnjica River, Q = 1363 m3/s. After the construction of dams, at the end of April 1979, because of inflow into the power plant system of Q = 1165 m3/s and simultaneous overflow at the Gorica Dam of Q = 812 m3/s, as well as flooding of the Trebinjsko Polje and parts of the Goric suburb, water penetrated many basements in Trebinje (Figs. 1.48 and 1.49).

1.6.3

Mokro and Petrovo (Dživarsko) Polje

Mokro (Wet) Polje is covered by fluvioglacial sands and pebbles, with a very small percentage of organic admixture. The thickness of fluvioglacial sediments is (most often) 1–5 m. They were deposited by flows that originated from the Wirmian glaciers at Orjen Mountain. Limestone paleorelief under these sediments is exceptionally karstified, with numerous lapies, ponors and estavelles. There are no permanent springs in Mokro Polje. Inflow into the polje and outflow from the polje occur exclusively

1.6 Karst Poljes

55

Fig. 1.46 Old mill constructed above the ponor on the left bank of the Pridvorci river-branch, 2021 (Photo Milanović)

underground, through numerous temporary springs, estavelles and ponors. Among the few temporary springs and estavells that are registered along the eastern rim of the polje, the most significant are Oko Rasovac (Fig. 4.1), Zbora (Fig. 1.52), Vučonica (Fig. 1.50a), Little Šumet (Fig. 1.50b), Uspotnica, Đurov do (Fig. 1.50c) and Prtenjača (Fig. 1.50d). In a period of heavy rainfall, water also flows out on the slope above Little Šumet. In part of Mokro Polje, which is covered with fluvioglacial sediments, and in Abatno Polje, estavelles in the form of funnel shaped depressions with a depth 2–5 m, are predominantly registered. They are mostly overgrown by vegetation (Fig. 1.51). The yield of each of these springs in the wet period of the year exceeds 5 m3/s. Maximum inflow in the polje is estimated at Qmax > 100 m3/s (Fig. 1.52). The most significant sinking sites are located along the eastern edge of the polje. Tracer tests established connections of this ponor zone with the spring zone of Duboka ljuta near

Plat, at the seacoast. The largest amount of water sinks through numerous estavelles below Zgonjevo but also directly, by percolation, through the fluvioglacial gravels and sands of huge permeability, which lie above karstified limestone. Cumulative sinking capacity of Mokro Polje is estimated at Q ~ 6 m3/s. In February 2021, a depth of flood water of 5.5 m was registered, which is probably close to the maximum possible level. Duration of floods in Mokro Polje range between 39 and 108 days. Figure 1.53 shows the flood that occurred in 1979. Then, the flood came close to the entrance of the St. Peter & Paul Monastery (~ 273 m a.s.l.). With construction of siphon culverts under the Gorica-Plat pipeline and excavation of the drainage canal through which the waters of this part of the polje are conveyed into the Trebišnjica riverbed, activity of the ponor zone is somewhat reduced but not eliminated. During the excavation of this canal, the presence of a ponor under the alluvial cover was

56

1

Natural Characteristics

Fig. 1.47 Trebinje town. Flood level carved on house wall

established (near the road between Trebinje and Dubrovnik). With dye tracing of Trap and Trnje ponors, the connection between the ponors was proven. The underground

connection of the ponor zone Zgonjevo—Luke with Duboka ljuta (Robinson) Spring is situated at the seacoast.

Fig. 1.48 Trebinjsko Polje, flood, 1979, panoramic view (Photo P. Milanović)

1.6 Karst Poljes

57

Fig. 1.49 Trebinjsko Polje. Flood in 1979. Left—area of Mostaći- Gomiljani, and right view from Mostaći to Volujac—Mokro Polje (Photos by P. Milanović)

The surface of the catchment area of Mokro Polje is about 90 km2. Annual precipitation exceeds 3000 mm in most of the basin (particularly in the Orjen Mountain area). Since the system of karst channels has been developed in carbonate formations below the bottom of the polje, a large amount of water from the Mokro Polje catchment area flows underground under the polje to the base level of erosion—the Adriatic Sea depression. After full saturation, the whole system comes under pressure and all estavelles start to work in the spring regime (mostly sublacustrine). After intense precipitation in conditions of full saturation of the karst system, pressure propagation occurs (piston effect), resulting in an almost simultaneous increase in inflow and rising flood levels. Several exploratory wells have been drilled in the background of the Oko Rasovac Spring (karst shaft), as well as in the region of Vučonica and Bašinići estavelles, and near the Potoci Ponor in the middle of Mokro Polje.

1.6.4

Bilećko Polje

Bilećko Polje, with an area of about 6.4 km2, of which 2.84 km2 is arable, is located above the Trebišnjica Springs (Fig. 1.54). It is slightly inclined towards the south, with an altitude of about 420 m. There are no surface streams or permanent springs in the polje, and the flood waters drain away by sinking in numerous ponors. Flooding problems are partially solved by construction of a short tunnel to the Bileća Reservoir. The polje was formed in plate-layered limestones of the Cretaceous age (Turonian). It was created in an earlier phase of evolution of the karst spring of the Trebišnjica River. The base of karstification was much higher, so discharge took

place along the current northern perimeter of the polje. The consequence of this process is numerous sinkholes on the surface of the field. Among these, Duboki do stands out, in which, before filling, was a water measuring device with reference point (zero elevation), 0 = 408.52 m. The fact that flows of hundreds of cubic meters of water per second pass under the polje, as well as the existence of the partially explored Dejan’s cave system, indicate the intensive karstification of the rock mass below the polje. This is confirmed by drilling boreholes PL-1 and L-1 to a depth of 150 m. Excepting detailed geological mapping of borehole core L-1 on three occasions (1974, 1975 and 1977), geophysical radioactive logging has been done. Gamma, gammagamma and neutron-gamma methods were applied. The presence of caverns was determined at depths of 36, 39, 43, 63, 78, 99, 102 and 105–106 m. These zones are matched with zones of increased water permeability (Lugeon test). Under natural conditions, the lowest parts of the polje, especially the bottoms of deep sinkholes, are occasionally flooded. After the formation of the Bileća Reservoir, frequency of the occurrence of water in the Duboki do (deep sinkhole) increased, so the analysis of these floods was given greater importance. A more detailed view of that flood is found in Chap. 5.

1.6.5

Ljubomirsko Polje

The temporary flooded Ljubomirsko Polje is located at an altitude of 530–520 m (Fig. 1.55). The area of the polje is 8.1 km2, of which 7.8 km2 is arable. It was formed along large fault zones in the Dinaric direction. Along this rupture, one of the most significant structures in this area is overthrusted— the Lastva anticline. The core of this anticline is composed of intensively crushed (grussified) Triassic dolomite.

58

1

Natural Characteristics

Fig. 1.50 Mokro Polje. (a) Estavelle Vučonica (b) Spring Small Šumet (c) Estavelle Djurov do (d) Estavelle Prtenjača, 2021 (Photos Milanović)

The northeastern rim consists of Jurasic dolomites as well as a large part of paleo-relief at the bottom of Ljubomirsko Polje. The northwestern part consists of karstified limestone. Due to grussification process these dolomites have certain retardation capacity so, in several locations along the rim, smaller springs were formed, some of which are tapped for local water supply (Fig. 1.56). In a dry period, their yield decreases below 0.5 l/s and some of them dry up. A large part of the polje is covered by alluvial sediments with a thickness of 2–7 m, with predominantly sandy-pebble material and decomposed dolomite with partly clay content.

In these sediments, a shallow aquifer is formed, which is used by shallow-dug wells (Fig. 1.57). The Brova stream is formed by a number of smaller springs in the Brani do dolomite massif. These dolomites are partially grusified, with a sand fraction, so there is possible accumulation of a certain water quantity. In the part of Ljubomirsko Polje that consists of dolomites, there are no ponors. The Ždrijelovići Ponor zone in the northwestern part of the polje is the main infiltration zone. This ponor zone is formed in karstified limestone. Water that sinks in the

1.6 Karst Poljes

59

Fig. 1.51 Mokro Polje. (a) Estavelle in Quaternary deposits of Mokro Polje (b) in Abatno Polje, 2021 (Photos Milanović)

Ždrijelovići ponor zone discharges along the right bank of the Trebišnjica River and flows toward the downstream part of Popovo Polje. During tracer tests of these ponors, the dye appeared in 14 springs and estavelles, from the Arslanagića bridge to the Dražin do. The largest amount of tracer discharged in the downstream springs. The best connection

was realized with the Tučevac Spring. Water discharges at the level of the Trebišnjica riverbed only in periods of high and medium groundwater levels. At low groundwater levels, it is possible there is circulation under the bed of the Trebišnjica River and water flows directly toward the Ombla Spring, but that link has never been proven with tracer

Fig. 1.52 Mokro Polje. Temporary karst spring Zbora. (a) Flood 1970 (b) Photo in dry period 2021

60

1

Natural Characteristics

Fig. 1.53 Mokro Polje. Flood in 1979 (a) Flooded area near St. Peter & Paul Monastery (b) Flood in the area of Gorica—Plat tunnel trace (pipeline section at surface)

tests. With this investigation, a connection is proven only with the valley of Trebišnjica. It is interesting that temporary surface flow of Brova flows toward the west; however, after sinking, underground water flows in the opposite direction, to the east and southeast (Fig. 1.57). By temporay torrent flow of Brova creek, the water inflow into Ljubomirsko Polje is Qav = 0.12 m3/s, but the total average estimated inflow in the polje from all sources, is Qav = 1.0 m3/s (Fig. 1.58). The possibility of construction of a small reservoir on the Brova torrent flow was mentioned for the first time in 1960. In the 1980s this idea about the possibility of constructing small reservoirs on the upstream part of Brova flow for irrigation and water supply of surrounding villages was reactivated. The hydrological gauge station (limnigraph) was installed but very quickly was damaged and became unusable. This investigation was never completed.

1.6.6

Fig. 1.54 Bilećko Polje. 1. Thin layer limestone, 2. Reverse fault, 3. Permanent karst spring, Qmax >100 m3/s, 4. Temporary karst spring Qmax >10 m3/s, 5. Temporary spring that exists in extreme flood cases, 6. Investigation borehole, 7. Tunnel trace from Fatnica Polje to Bileća Reservoir, 8. Bileća Reservoir

Ljubinjsko Polje

The Ljubinjsko Polje belongs to closed karst poljes whose longer axis is in the Dinaric direction. The area of the polje is 8.5 km2, and the field is continuously inclined tothe northwest. The cultivated surface area is evaluated at 7.7 km2. Between the end points of the polje (along the longer axis), the height difference is 54 m (from 472 m above sea level in the eastern part to 398 m a.s.l. in the lowest, western part of the polje). From a hydrogeological viewpoint, the polje represents a kind of hydrogeological enclave. This hydrogeological individuality is reflected, above all, in the isolation of its basin from the basins of other, upstream karst poljes. Unlike most karst poljes of East Herzegovina, there is no significant

1.6 Karst Poljes

61

Fig. 1.55 Ljubomirsko Polje. 1. Clayey-sandy sediments, 2. Triassic dolomites, 3. Karstified limestone (J, K), 4. Overthrust and normal faults, 5. Direction of underground flows, 6. Temporary surface flow, 7. Group of close ponors

permanent or temporary spring. The water inflow into the polje occurs exclusively by Bukov creek torrent flow. Drainage of the polje occurs by water sinking into the ponors located in the western part of the polje (Fig. 1.59). The polje is created in Upper Cretaceous limestone. The bottom is covered with alluvial deposits. From the northwestern end of the polje towards the Deransko Blato, zones of Eocene limestone are discordantly inserted along the reverse structures. In this part of the polje, the wider zone of the Konac Ponor (401 m above sea level), a thickness of clayey sediments of 64 m was determined by drilling. The polje is temporarily flooded with water from Bukov creek. According to records of ancient resarchers, the duration of earlier floods in this polje was much longer. This is from the data of J. Cvijić. The abbreviation of earlier long-term floods can be explained by more significant alluvial ponors that were walled around 1920 and later, unhindered drainage taking place. In current conditions, floods are rare, and the duration of a flood is not more than 10–15 days. The maximum height of the water column in the lowest part of the polje, around the Konac Ponor, is about 5 m. Limitation of floods, in time and

height, is certainly a consequence of hydrogeological isolation and a small catchment area. Measuring flow at the Bukov Potok hydrological gauging station (February 19, 1986), the established quantity was Q = 1.44 m3/s. Since the local catchment area between this gauging station and the polje itself brought an additional amount of water, it can be assumed that flooding in the lowest part of the polje started when inflow ranged between 2 and 3 m3/s. According to earlier hydrological assessments, inflow into the ponor zone never exceeded 5 m3/s. A tracer test of the Konac Ponor was done on 22 December 1960, with 136 kg of Na-fluorescein (Fig. 1.31). It is estimated that during the test time, inflow into the ponor was 0.5 m3/s. Seven hours after the dye was injected, flow into the ponor stopped. Sampling points were as follows: four springs in Deransko Blato; six springs in Svitava; seven springs along the Neretva valley (from Doljani to Bađula); twelve springs and submarine springs on the coast of the sea from Bistrina to Ombla; three estavelles near Strujići; and, in the Bregava valley, at the Do gauging station. The possible presence of

62

1

Natural Characteristics

Fig. 1.56 Ljubomirsko Polje, Marojevića Spring, 2007 (Photo P. Milanović)

dye is indicated only in one sample from Meginja (Strujići), which was taken on January 18, 1961 (0.5 mg/m3). That sample is questionable. Eight main springs were observed until May 22, but the presence of dye was not determined in any sample. At the time of taking the samples, Meginja was submerged by the flood waters of Popovo Polje. The possibility of dam construction to achieve a small reservoir in the dolomites of the valley of Bukov creek was analysed a few times. This will be discussed in more detail in Sect. 4.4.8.

1.6.7

Fatničko Polje

Fatničko Polje is a closed karst polje, with an area of 5.6 km2 and at an altitude of 470 m. The polje is situated in the central part of East Herzegovina and represents the most significant hub of underground flows in this area. During his travels in East Herzegovina in 1897, J. Cvijić studied Fatničko Polje in detail, especially the morphology and hydrographic conditions, which he published in the paper, “Karst Poljes of Western Bosnia and Herzegovina”, 1900 (Fig. 1.60). The polje is created along a reverse fault with dinaric direction along with northeastern rim (Fig. 1.61). Along this fault, Cretaceous limestone are overthrusted over Eocene flysch. The bottom of the polje consists of Tertiary lake

sediments. By geoelectrical sounding and investigative drilling (borehole FP-1), it was established that the thickness of these sediments in the southeastern part of the polje reaches 108 m. During drilling of the borehole, a methane eruption occurred. This indicates the presence of sediments of organic origin. The greatest depth of these sediments extends along the northeastern edge, below the village Fatnica, with a width of about 200 m and a length of 2200 m. Geoelectric investigations show that the depth of this zone ranges between 130 and 140 m. In this area, limestone is detected by borehole, at a depth of 167.3 m. It is obvious that space for deposition of these sediments is created close to the northern block of the reverse fault. Between these two zones, in the paleo-relief, there is a limestone ridge, at a depth of 26.1 m (borehole FP-2). The most significant spring zone consists of temporary springs on the northeastern rim of the polje—Obod, Baba Jama and Pribabići. The elevation of the Obod dam crest is 476.26 m, and the opening of Baba Jame is at 476 m a.s.l. The elevation of the Lepernica estavelle is 471 m. The maximum measured discharge of the Obod Spring is 35.8 m3/s; however, the maximum discharge of this entire spring zone is estimated at about 60 m3/s (Fig. 1.62). A large number of tracer tests determined that a large catchment area gravitates toward the Obod Spring (Gradina

1.6 Karst Poljes

63

Fig. 1.57 Ljubomirsko Polje. Dug well in sandy pebble sediments (Photo by P. Milanović)

between Nadinići and Fojnica, and catchments of Gatačko and Cerničko poljes, Fig. 1.61). The lowest point in the polje is the Pasmica Ponor, at an altitude of 462 m (Fig. 1.63). A permanent water gauging station, including a concrete overflow structure, is in front of the Pasmica Ponor, with zero elevation 0 = 462.54 m (Fig. 1.64). As part of the investigation into the needs of the Trebišnjica Hydrosystem, in addition to the three boreholes already mentioned in the polje itself (flooded area), six more were drilled (F boreholes) above the level of the flood waters. These boreholes are located along the southwest rim of the polje to analyze the hydrogeological characteristics of the Pasmica ponor zone and to investigate bifurcation zones in the background of the southwest rim of Fatničko Polje (Fig. 1.65). Deepts of these boreholes are as follows: F-1228 m, F-2185 m, F-3265 m, F-4144 m, F-5200 m and F-6165 m. All these boreholes are equipped with piezometric pipes. Piezometer F-5 was equipped with a limnigraph.

Two piezometers, OK-1 and OK-2, were constructed in the background of the temporary Obod Spring. The purpose of these piezometers was to measure the pressure on the Obod channel. However, very fast flow (~16 m/s) carrying huge pebble pieces destroyed the flow measurement instruments that were previously installed in the outlet section of the Oboda channel. Speleologists could not penetrate the Obod karst channel deep inside because they very quickly came across siphon lakes. Only cave divers were able to investigate part of the northern channel (see Sect. 3.1.6). In order to control filtration between the Dabarsko and Fatničko poljes along the limestone ridge (Ljut), six boreholes were drilled between the poljes: D-1, D-2, K-2, DF-1, DF-2 and DF-3. An absolute relationship exists between the beginning of the Obod temporary spring and the water level at the Srđevići gauging station in Gatačko Polje (Fig. 1.66). This dependency played an exceptional operational role in managing the operation of the power plant system, especially

64

1

Natural Characteristics

Fig. 1.58 Ljubomirsko Polje. Brova creek in Jurassic dolomites, 2007 (photo Milanović)

in the winter period when it was important to provide the necessary space in the Bileća Reservoir, in order to accept waters of the incoming rainy wave. Anidea to seal the Obod Spring to prevent groundwater discharge into the Fatničko Polje was not successful (more detail on this in Sect. 4.8.1). Below the village of Fatnica and in the extreme northwestern corner of the polje, there are several smaller temporary springs, among which the Mačkovac and Zla stijena are more significant. They are located opposite of the Kutske Jame Ponor in Dabarsko Polje. According to Cvijić (1900), “They are active only when there is water in Dabarsko Polje because they are lower than the Kutske Jame (Kutske Pits) and for sure are connected, as it is opinion of local people”. However, this connection was never confirmed, despite tracer tests of the Kutske Jame (1956) and later observations. The position of smaller permanent and tapped springs (Kamenik, Kukolj, Jastrebnjak and Studenac) along the

northern perimeter of the polje is a consequence of the position of an impervious flysch zone. These do not have any impact on polje floods. A curiosity is a small spring, situated right above the Obod temporary spring. This small spring was tapped because it never dries up. A tower for investigation purposes was built on the Pasmica Ponor. It is equipped with tubes for tracer tests and for inserting a geo-bomb during the flood period (Fig. 1.67). Maximum swallowing capacity of this main opening of the ponor is about 25 m3/s, but the entire ponor zone is about 120 m3/s. This sinking capacity is possible at a time of maximum flood level, and simultaneous low level of underground water in the area of Fatničko Polje. Determining the spatial position of karst channels using a geo-bomb was successfully applied for the first time in Fatničko Polje on January 17, 1974 (Aranđelović et al., 1976). The route of the channel of the Pasmica Ponor was

1.6 Karst Poljes

65

Fig. 1.59 Ljubinjsko Polje. Western part of the polje, with Konac Ponor (the largest) and the ponor section in the lowest part of the polje, 2021. (Photo Milanović)

followed for a few hundred meters. It was later confirmed by construction works in the entrance area of the Fatnica— Bileća tunnel (Fig. 1.68). The largest estavelle zone is Lepernica, approximately in the middle of the southwestern perimeter of the polje, below the Velika Pećina (Grand Cave). This zone is located at an altitude of approximately 471 m. Estavelles Big and Little Nežir are located northeast of the Pasmica ponor zone, along with the polje perimeter.

Fig. 1.60 Fatničko Polje. Cvijić (1926)

Detailed measurements were done in 1971/72. It has been established that all ponors and ponor zones in this polje often work in the regime of springs. During these investigations, there was continuous monitoring of the water level at the Pasmica gauging station and the groundwater levels in piezometers F-1, F-5 and OK-2. In these periods, the inflow into the polje was almost twice as large as when Pasmica is exclusively in the regime of the ponor (1970–1973, Institute of Hydrotechnics, Sarajevo).

66

1

Natural Characteristics

Fig. 1.61 Area: Gatačko Polje—Fatničko Polje—Trebišnjica Springs. 1. Limestone and dolomites, 2. Flysch, 3. Promina conglomerates, 4. Great permanent spring, 5. Great temporary spring, 6. Great spring— cave, 7. Small permanent spring, 8. Small temporary spring, 9. Great

ponor, 10. Ponor, 11. Group of close ponors, 12. Boreholes, 13. Established underground link, 14. Temporary flow (Milanović, 2006, 1980)

Long-term observations of GWL fluctuations in piezometric boreholes around the perimeter of the polje (organized by HET) showed that after intense rainfall, the GWL south of the Pasmica ponor zone suddenly reaches an elevation higher

than flood water elevation. So, for example, after 5 days of precipitation, a total of 160 mm, the level water will rise: – in F-3—97 m (from 373 m to 470 m) – in F-5—82 m (from 388 m to 470 m)

1.6 Karst Poljes

67

Fig. 1.62 Obod Spring. (a) Dam (ancient overflow structure) with mills in dry period, 1979 (b) Overflow during a period of high spring discharge 1980 (Photos Milanović, 1979)

The southwestern perimeter of the Fatničko Polje has the role of a wide watershed and bifurcation zone. Water which sinks along this rim mostly flows in the direction of the Trebišnjica Springs, but one part flows in the direction of Bregava springs. This was established by tracer tests, including application of Na-fluorescein and lycopodium spores (Fig. 1.69). Flow in the direction of Bregava Springs is only possible when the Lepernica estavelle zone is submerged by flood water and when its function is in regime of ponor. It is estimated that, under these circumstances, 10% to 15% of flood water accumulated in Fatničko Polje can flow in the direction of Bregava Springs. Fatničko Polje is one of the most frequently flooded poljes. Flood levels are very high, and the duration of floods is very long. The maximum flood levels were recorded by Balif— 28.8 m (1888) and Cvijić—40 m (1897). According to data from the Hydrometeorological Service of Bosnia and Herzegovina, the depth of flood water on 30.12.1950 was 38.30 m, and the volume of accumulated water was 228 × 106 m3. On the velocity of flood water rise and the intensity of polje dewatering of greatly influence is maintenance of numerous ponors against plugging. In the notes of his visit,

Cvijić (1900) mentioned Austrian engineers Andreaš and Balif who, in the period 1890–1900, intensively worked on improving ponor drainage capacity in the Fatničko Polje. Before construction of the Grančarevo Dam and formation of the Bileća Reservoir, the duration of floods was between 73 days (1953) and 194 days (1960). After the formation of the reservoir, the periods without floods are, on average, shortened by a month, compared to natural conditions. In the period between 1968 and 2004, floods lasted from 51 days (1992) to 235 days (1979), with a maximum flood water depth of 33.82 m (1970). The average duration of floods is 125.3 days per year (Table 1.8). The longest continuous flood lasted 7 months (1950/51 and 1969/70). Figures 1.70 and 1.71 show photos of several floods. The average medium inflow in Fatničko Polje, for a period of 40 years, is Qav = 9.7 m3/s. Maximum registered inflow was 29.9.1984, Qmax = 261 m3/s. The hydrogeological and hydrological characteristics of Fatničko Polje are certainly the most complex in East Herzegovina, as well as in the karst of the Dinarides. One of hydrogeological specificities of Fatničko Polje is that, in a period of great precipitation, the entire polje comes under pressure, i.e., all ponors and estavelles function as springs, so the rise of flood water in that period is much faster. The crucial cause of this occurrence is insufficient drainage

68

1

Natural Characteristics

Fig. 1.63 Fatničko Polje. 1. Tapped spring, 2. Permanent spring, 3. Temporary Spring, 4. Great temporary spring, 5. Estavelle, 6. Group of nearest estavelles, 7. Ponor, 8. Group of close ponors, 9. Largest ponor (Pasmica), 10. Cave, 11. Shaft, 12. Sinkhole, 13. Temporary river flow, 14. Eocene flysch, 15. Eocene limestone, 16. Cretaceous limestone (Milanović, 1979)

capacity of channels downstream from the polje toward the springs of the Trebišnjica River. They cannot accept the inflow of large amounts of water from the Fatnčko Polje and from the local catchment area, so all ponors are in the water regime of springs (schematic shown in Fig. 1.72). In the dry period, only deep underground flows with a free surface are active, Fig. 1.72a. When discharge starts (on the Obod spring) and sinking (in the Pasmic Ponor), the inflow and outflow of water are still unconfined (with free surface) because there is far less transmission capacity of drainage karst channels (Fig. 1.72b). With an increase of inflow (Fig. 1.72c), the downstream channels come under pressure,

while in the upstream part, the aquifer is still partially saturated. When congestion (clogging) of channels starts, between Fatničko Polje and Trebišnjic springs, the ponors in Fatničko Polje are not able to absorb all the water and flooding occurs. The piezometeric line is still inclined towards the spring zone (1) When the quantity of inflow from the direction of Gatačko Polje increases and the precipitation between Fatničko Polje and the downstream spring zone is greater than 100 mm/24 h, the level of underground water in the downstream portion of the aquifer becomes higher than the level of flood water in the polje (Fig. 1.72d). Then, all the

1.6 Karst Poljes

69

Fig. 1.64 Fatničko Polje. Hydrometric gauge station in front of Pasmica Ponor and tower structure with launching pipes for geo-bomb and tracer injection during floods, 1972 (Photo Milanović)

ponors, including Pasmica, are in regime of springs and, at a number of places on the slopes above the Pasmica zone, water erupts (fountains) under pressure (Fig. 1.73). In that period, the flood level rises faster than if it is a consequence of inflow only from springs (Obod and Baba jama). In certain periods, there is an established balanced stage, when there is neither inflow nor outflow, but it lasts for a very

short time. Avdagić (1973) registered a period of 4 days during the flood in 1971 when there was no inflow or outflow from Fatničko Polje. The Fatničko Polje has an exceptional management role in the operation of hydropower plants. The polje has been the subject of investigation and analyses for numerous studies and scientific research for more than 50 years.

1.6.8

Fig. 1.65 Position of investigation boreholes. 1. Boreholes, 2. Karst shaft, 3. Cave, 4. Large temporary spring, 5. Ponor Pasmica (Milanović, 2006)

Dabarsko Polje

Dabarsko Polje belongs to the Bregava watershed (Fig. 1.74). The length of Dabarsko Polje is about 20 km, the average width varies between 1 and 3 km, and the surface is 33 km2 of which 28.1 km2 is arable. The Polje is slightly inclined in a NW–SE direction, from an elevation of 551 m at very northwestern part (Potkom) to the lowest points, the Ponikva Ponor (471 m a.s.l.) and Kutske Jame (472 m a.s.l.) in the eastern part of the polje. The polje is formed along a reverse fault, along the northeastern edge of the polje, along which the Fatničko Polje was also created (Fig. 1.75). As already mentioned, the inclination of the reverse fault surface varies between 60° and 70° in a northeast direction. Results of geoelectrical sounding depth of Tertiary sediments that are deposited into the depression of the Dabarsko Polje shows ranges between 200 and 300 m (Strupići–Hatelji), and in the area of the Ponikva Ponor, it is greater than 400 m. According to the same investigations, the bedrock of these sediments in the northwest part of the polje consists of Promina conglomerates. The high and steep

70

Fig. 1.66 Relation between inflow into Fatničko Polje and flow at the water gauging station at Srdjevići ponor in Gatačko Polje (Avdagić, 1973)

massif of the northeastern edge of the polje, from Kutske Jame to the village of Hatelji, consists of Cretaceous limestone. Further, to the very northwestern part of the polje, the mountain slope of Trusina Mountain continues, which consists of Promina conglomerates. Flood levels are controlled by Kuti water gauging stations (founded in 1888) and the Ponikva hydrology station. The most significant flow that causes flooding is torrential flow Opačica (Fig. 1.76), which starts in Trusinsko Polje. It spills into the central part of Dabarsko Polje, provoking a flood. The most important permanent spring is Vrijeka. Close to Vrijeka are temporary spring Sušica, permanent spring Pribitu and the Ljelješnica estavelle (Fig. 1.77). Hydrological processing of data from water gauging stations Kuti and Ponikva shows that floods last from 42 to 216 days per year (Fig. 1.78). The average flood lasts 110 days, and water depth reaches 14 m (Milićević, 1987). A comparison of average yearly flood duration for 1949–1967 (108 days) with the period 1968–1982 (135.7 days) is interesting. In the first period, not a single day of flooding was recorded in July, August and September. In the second period the time without single day of flood has been recorded in July and August only. The most significant is the only permanent spring— Vrijeka (Vrioka) (photos in Figs. 1.79 and 1.80). From the

1

Natural Characteristics

Vrijeka spring to the Ponikva Ponor, the total length of the stream is about 2.5 km. Flow discharge of the permanent Vrijeka River varies from about 25 m3/s maximum to 43 l/s extreme minimum (13.08.2003). Summer minimums are most often around 100 l/s, up to 150 l/s. From Sušica Spring (cave) towards the Berkovići settlement, at a distance of approximately 100 m, there is the Pribitu Spring (Fig. 1.81). The measured yield of this spring in the dry period is 17 l/s (D. Vujović, HET). The Bezdano spring zone consists of a few small springs that are connected with simple drainage, in the unique tapping structure. Due to small quantities of water, it is hard to believe that the water from this discharge source could have satisfactory drinking water quantity and quality. Tertiary sediments of the Dabarsko Polje (except for the surface layer, with a thickness of 10–20 m) are practically impermeable, so a significant aquifer is formed in the surface layer. Water feeding this aquifer originates from the waters of Opačica flow and direct precipitation. In this zone there are dug wells with a depth of 20 m. The most significant are Valjendža and Oko (downstream from Valjendža). For the purpose of measurement, the inflow in 1959 was established from hydrological water gauging stations Vrijeka, Ljelješnica and Blace. The average inflow in Dabarsko Polje, calculated for a period of 40 years is Qav = 6.90 m3/s. The polje is naturally drained through the Ponikva Ponor, Kutske Jame Ponor, Strupići ponor zone and Ljelješnica estavelle. The cumulative maximum capacity of the Dabarsko Polje ponors is about 42 m3/s. The Ponikva Ponor, on the southeastern perimeter of the polje consists of two cave openings (Fig. 1.82). The surface of the entrance of the eastern Ponikva channel is 8.43 m2. The size of western opening is something smaller. In a period of extremely heavy rainfall, Ponikva Ponor can work in regime of spring; however, the duration of discharge is very short. For instance, in the winter period of 1969–1970 Ponikva lasted in regime of spring 6 days. In this period, the maximal recorded discharge was about 12 m3/s (Avdagić, 1973). Tracer investigations established that almost all sinking waters in Dabarsko Polje discharged at the springs of Bregava. On their way to the Neretva River, a large part of this water percolates along the Bregava riverbed and flows towards Hutovo Blato. There is an indication that a small part of the water that sinks in Dabarsko Polje flows directly to the Deransko Blato, but this is not proven (Fig. 1.83). By dye tracing in the low water stage, when water was sinking only in the left (eastern) opening of the Ponikva Ponor, a connection with the Bitunja Spring in the Bregava valley was established. By tracer test, in a period of flooding when both openings of the Ponikva Ponor were submerged,

1.6 Karst Poljes

71

1.6.9

Fig. 1.67 Fatničko Polje. Investigation tower at Pasmica Ponor (Photo Milanović, 1971)

the connection with Bitunja, Big and Little Suhavić springs was established.

Cerničko Polje

Cerničko Polje is one of the smaller karst poljes, with an area of about 3 km2. It is situated between the hypsometrically higher Gatačko and lower Fatničko Polje. In the documents, “Meliorative-power system in East Herzegovina” (published in Sarajevo, 1960) and “Water management base of the karst poljes of East Herzegovina” (published in Trebinje, 1967) construction of HPP Cernica in Cerničko Polje was foreseen. According to these documents, Cerničko Polje was chosen for a man-made reservoir in this area and was geologically mapped in detail, including geophysical surveys. In the polje area, eight investigation boreholes (CB-1, CB-2 and CA-1 to CA-6) were drilled. The boreholes are located along the southern edge of the polje and in the hinterland of the Jasovica ponor zones, including the area of the Ključki Ponor, into which sinks the Ključka River (Fig. 1.84). The polje was formedthrough erosion of a narrow flysch zone, with a length of about 5 km. This is in contrast with the pronounced high limestone section along the face of the reverse fault, along which Jurassic limestones overlaid Eocene flysch. In addition, the reverse (northern) block was exposed to strong horizontal pressures that formed a local fold, with an axis perpendicular to the direction of faulting and approximately perpendicular to the dinaric direction (Fig. 1.85). The eastern limb of this fold (anticline) is extremely tectonized. Along it, there is a developed zone with karst channels, with large flow capacity from the ponors Jasikovac and Vranjača in Malo Gatačko Polje, flowing to the large spring Vilina Pećina (Fairy cave) at the northern perimetar of Cerničko Polje.

Fig. 1.68 Fatničko Polje during flood time. (a) Activation of the geo-bomb immediately before it was inserted into the ponor (b) Geo-bomb, Aranđelović et al., 1976. (Photo by Milanović 1974)

72

1

Natural Characteristics

Fig. 1.69 Watershed zones in the region of the Fatničko Polje. (a) Layout 1. Permanent Spring, 2. Temporary spring, 3. Ponor or estavelle, 4. Established underground water links, 5. Color of spores, 6. Watershed

zones Color of spores: (Z) green (C) red (P) blue (N) non-colored and (V) violet. (b) Cross-section from Trebišnjica Springs to Bregava Springs (Milanović, 1979)

The depth of the flysch was determined, through geophysical research, to be about 200 m. This flysch zone is a hanging hydrogeological barrier, over which the part of the water that sinks into Malo Gatačko Polje discharges at the surface, as the Ključka River flows to the largest ponor in Cerničko Polje (Figs. 1.86 and 1.87). In the dry season, almost all the waters of the Gatačko Polje basin flow below or around this barrier, toward the Trebišnjica springs. The polje floor is uneven, with a large number of gullies connecting temporary springs situated along the northern edge of the polje, with ponors along the southern edge. The most significant flow is the Ključka River which discharges from Vilina Pećina (Fairy cave). In summer the river flow decreases to a dozen liters, and in winter it is more than 20 m3/s. The length of the Ključka River is about 300 m (Fig. 1.87).

After flowing over the flysch, the river plunges into the ponor of the Ključka River at an altitude of 818 m. The ponor was formed in karstified Cretaceous limestone (Fig. 1.88). In front of the ponor, there is a concrete water gauging station (uverflow), equipped for monitoring. During high discharge from the Fairy cave, whose maximum estimates are more than 50 m3/s, far exceeding the swallowing capacity of the Ključki Ponor, retention at the ponor zone is created. Rising floodwaters submerge the western part of the polje toward Stepen, including the lowest part of the polje, known as ponorine—the area with a number of the closest ponors. These waters sink through a series of ponors along the southern rim of Cerničko Polje, the most significant being the Jasovica (Fig. 1.89) and Šukovića ponors. The ponors of the Cerničko Polje—the Šukovića Ponor and the Jasovica Ponor (810 m above sea level)—are

1.6 Karst Poljes

73

Table 1.8 Flood duration in Fatničko Polje from 1968 until 2004 Source HET 1968 1969 1970 1971 1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 Σdays Average. Monthly

I 31 31 31 31 3 6 23 – – 31 13 31 25 25 31 18 24 7 31 20 15 – – 2 – – 31 12 31 31 8 11 31 31 – 31 14 660 17.8

II 26 24 28 28 18 12 15 – – 28 24 28 16 6 9 14 9 17 28 28 22 2 – 6 – – 9 7 29 11 – 13 7 28 8 16 13 529 14.3

III 5 31 31 20 24 4 8 13 7 31 31 31 9 28 2 6 7 16 31 14 14 25 2 – – – – 9 12 – – 20 1 31 3 – 31 502 13.6

IV – 30 30 30 13 21 – 22 8 30 30 30 12 30 18 22 30 10 30 29 30 6 12 11 18 9 20 8 30 8 8 19 16 26 10 4 30 695 18.8

V 14 15 31 16 4 8 – – 14 7 31 31 24 23 – 3 20 5 29 8 14 – 5 14 – – 19 13 29 11 3 10 – 70 – – 31 425 11.5

VI – 11 21 – – – – – – – 27 9 8 – – – 2 – – – 3 – – 2 – – – – – – – – – – – – 10 107 2.9

VII – – – – – – – – – – – 8 – – – – – – – – – – – – – – – – – – – – – – – – – 8 0.2

VIII – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – –

IX – 10 – – 3 – 5 – 12 10 – – – – – – 6 – – – 10 – – – – – – 16 11 – 4 – – – 6 – – 93 2.6

X – – – 5 – – 31 19 14 15 15 6 15 7 4 – 31 – – – – 15 – 13 13 9 – 1 24 – 31 1 13 – 22 9 9 322 8.7

XI 21 5 15 10 14 – 30 23 30 14 – 30 26 – 11 2 13 21 2 7 8 6 6 26 20 25 2 2 9 22 30 14 25 17 17 25 17 545 14.7

XII 31 31 5 30 8 11 31 23 31 27 17 31 31 23 17 14 8 26 – 31 24 – 31 31 – 31 – 19 31 17 20 31 13 10 7 31 30 752 20.3

Σ of days 138 188 192 170 87 62 143 100 116 193 188 235 166 142 92 79 150 102 151 137 140 54 154 105 51 74 81 87 206 100 104 119 106 150 73 116 185 4638 125.3

max flood (cm) 2166 1896 3382 2382 1400 1602 2725 1535 2618 2566 2282 2609 2570 2233 2550 1715 1640 1904 2827 2141 1776 1498 1478 2637 1187 1725 2007 1403 2443 2225 1778 2644 2744 2418 1738 1956 1858

With bold are presented absolute recorded maximum (3382) and absolute recorded minimum (1187)

confirmed, through dye tracing, to be underground connections of Cerničko Polje with the temporary springs Obod and Baba Jama in Fatničko Polje and the springs of the Trebišnjica River. Floods in Cerničko Polje are hydrogeologically and hydrologically related to floods in Malo Gatačko Polje. Depending on the inflow into the polje, the flood begins first through the Fairy Cave and the Stepenički stream, and it flows from the polje through the Ključki, Jasovica and Šuković ponors (Fig. 1.90).

After the concept of using water that flows in the direction of Gatačko Polje—Cernica–Fatnica was abandoned, flood monitoring in the polje was practically cancelled for a long period of time. With an increase in interest for Cerničko Polje to be used as storage space (or retention), a program of additional investigation started (drilling of IBP boreholes), as well as observation of the water regime in the polje. An automatic hydrological station was built on the ponor of the Ključka River. Analysis of the flood in recession conditions, for the period of extreme rainfall in 2010, was carried out for the

74

1

Natural Characteristics

Fig. 1.70 Fatničko Polje. Early stage of flood, 2005 (Photo Milanović)

Fig. 1.71 (a) Fatničko Polje in flood conditions (1971); (b) Ponor zone Pasmica submerged by flood water (photos P. Milanović)

1.6 Karst Poljes

75

Fig. 1.72 Fatničko Polje. Change of function of sink zone into the spring zone. Schematic of cross-section between Cerničko and Fatničko Polje and change of ponors into springs a, b, c, d (P. Milanović, 2020)

period of time that flood waters lowered from an elevation of 849.18 m (06.12.2010) to an elevation of 831.78 m (12.12.2010). The initial depth of floodwater above the lowest point of the polje (816 m above sea level) was about 33 m. At that elevation, the flooded surface was 3.55 km2 and stretches west from the Ključki Ponor (to Zagradci). For the

selected lower elevations the flood water surfaces are: for elevation 840 m–2481 km2, and for elevation 834 m– 1518 km2. On the basis of the collected data, the runoff from the polje was calculated, i.e., swallowing capacity of the ponor zone (technical services HET). During a decrease of flood level

76

1

Natural Characteristics

Fig. 1.73 Fatničko Polje, 1974. Water jet at the hill slope above the Pasmica Ponor area and vortex in the same zone due to sinking, 2 days later (Photo in the corner) (Photos Milanović)

from 849.18 m a.s.l. to 831.78 m a.s.l., it was estimated that the total average cumulative capacity of all ponors was around 80 m3/s.

1.6.10 Gatačko Polje The Neogene sedimentation trench of Gatačko Polje was formed along the reverse fault, Pusto Polje—Gradina— Bijena. The surface area of Gatačko Polje is 37.6 km2 (Figs. 1.91 and 1.92). The limestone ridge between Fazlagića Kula and Srđevići divides it into Veliko Gatačko Polje (area 31.83 km2) and Malo Gatačko Polje (area of 5.77 km2). The elevation of Gatačko Polje ranges between 950 and 936 m. The northern edge of Gatačko Polje is built by Jurassic limestone with chert. Further towards the mountain pass Čemerno and the Neretva River, a geological formation known as Durmitor flysch continues. This formation consists of two main lithofacies, limestone and sandy-clay. This flysch formation is very much faulted and folded. Thickness

of the limestone sequence ranges from tens of meters to over a hundred meters. These limestones are extremely karstified, with numerous sinkholes and ponors (swallow holes). Each of these sequences issandwiched between sandy-marly zones inside of them, withtypical karst circulation, almost exclusively in the strike direction of these structures. On October 12, 1972, a relationship between the Blace Ponor (Ponikve area, north of Gacko urban area) and the Vjetrenik Spring (Gračanica riverbed) was established, through dye tracer testing. The previously mentioned sandy-marly facies, in which the dominant structures are conglomerates, microconglomerates, grauwacke, siltstones, sandy marls and marls, have a key hydrogeological role in the formation of the Klinje and Vrba man-made reservoirs. Layered dolomitic limestones of the Upper Triassic and detrital limestones of the Liassic and Doger build the northern slopes of Gatačko Polje and the substratum of Mesozoic karstified limestone. These are relatively poorly permeable rock masses, in which local and disconnected aquifers are

1.6 Karst Poljes

77

Fig. 1.74 Dabarsko Polje. Western part of the field, 2018 (Photo Milanović, 2018)

Fig. 1.75 Dabarsko Polje. 1. Cretaceous limestone, 2. Promina conglomerates, 3. Eocene flysch, 4. Ponikva ponor, 5. Great permanent spring, 6. Great temporary spring, 7. Small temporary spring, 8. Ponor,

9. Group of close ponors, 10. Great temporary spring—cave outlet (Milanović, 1980)

78

1

Natural Characteristics

Fig. 1.76 Dabarsko Polje. Channel of torrent flow Opačica River in a dry period, 2009 (Photo Milanović)

created. These aquifers are discharged through several springs, the most important being Srnj, Lijenj, Slavljan and Lipnik. The Srnj Spring is also tapped, and for a long time was used as a water supply for the town of Gacko (until the construction of the water intake at Gračanica Spring— Vratlo). Results of geophysical investigations indicate the total thickness of clastic (Cretaceous) and Neogene sediments in Gatačko Polje to be approximately 800 m. The existence of Cretaceous flysch beneath Neogene sediments in the western part of the polje was confirmed by micropaleontological analyzes of the drilling core from deep boreholes. Neogene sediments, with a maximum thickness of about 450 m, contain a coal-bearing series whose depth reaches 240 m. Based on the lithological and paleontological analyzes, R. Milojević divided the Neogene series into 13 lithostratigraphic units, in which there are three coal seams (I and II bottom and main coal seam) and one coal

seam zone with impure coal and carbonaceous marls (Dedić & Ostojić, 1981). The lowest, basal zone makes grey-green clay, with layers of tuff and conglomerates (thickness 20 m), above which lies the II coal seam (max 10–15 m thick), followed by gray friable marls (30 m), I lower coal seam (5 m), gray limestone marl (2–30 m), main coal seam (12–25 m), gray limestone marls (20 m), gray clay marls (thickness up to 140 m), tuffitic level (15 m), the lower striped coal level of the upper coal series (15 m), the middle coal level of the upper coal zone (25 m), the upper stripe coal level of the upper coal zone (20 m) and clays and marls of the final zone of the Neogene series, which are preserved only in the small space in the center of the basin. Geological reserves of coal are estimated at 480 × 106 tons. Research for exploitation of the Gračanica open mine has shown that the best accumulation capabilities have part of the Neogene series that includes I lower coal seam, gray marls and the main coal seam, up to a depth of approx. 40 m. The

1.6 Karst Poljes

79

Fig. 1.77 Dabarsko Polje. (a) Hydrogeological sketch map. 1. Permanent karst spring Qmax > 20 m3/s, 2. Permanent spring with a few liters per second at minimum, 3. Large temporary spring, 4. Large ponor with

swallowing capacity more than 20 m3/s, 5. Ponor, 6. Investigation boreholes, 7. Drilled well, 8. Cave, 9. Estavelle. (b) Photo—Estavelle Ljelješnica (Photo Milanović, 1970)

most important feeding by water of these zones is in the places where they are exposed on the surface of the terrain and also inplaces where they are in direct contact with limestone on the edge of the polje (Dedić & Ostojić, 1981). Permanent river Mušnica flows through the polje. Itis formed from the three streams whose springs are under Čemerno and Lebršnik Mountain. These are the Vrba, Ulinje and Jasenica creek, with its tributary the Žanjevica creek. It is an interesting fact that long term measurements of minimal flow of the Mušnica River show that, between the Avtovac and Srđevići gauging stations, it sinks about 0.05 m3/s on average. Also established is the presence in the ponor of marls and shallow underground flow. In one of these ponors (at the old bus station in Gacko) a tracer was inserted, and its connection with the Mušnica riverbed was established. In the area of the Malo Gatačko Polje tectonic rift, along the Gradina—Pusto Polje, discontinuity of one of the most concentrated infiltration zones of this area is formed from the Srđevići Ponor to the Šabanov Ponor, which is the lowest ponor in Malo Gatačko Polje (Fig. 1.92). Ponors were formed along the southwestern edge of Malo Gatačko Polje in very karstified Cretaceous limestone. In the current conditions, with submergence of approximately 6 m of floodwaters, an infiltration area is activated, whose

maximum sinking capacity reaches 160 m3/s in the most favourable hydrogeological conditions. For many years, the Srđevići Ponor (estavelle) was considered to be the largest ponor, based on the sinking capacity in the area of Malo Gatačko Polje (Fig. 1.93). New investigations established that the Jasikovac—Vranjača ponor zone represents the most significant ponor zone in the Malo Gatačko Polje. Due to works in the area of the open mine at the Gacko thermal power plant and the blocking of the Srđevići Ponor, its swallowing capacity is significantly reduced, compared to natural conditions. The existing swallowing capacity of the Srđevići ponor has not been precisely determined, but it is probably not more than 10 m3/s. In conditions of complete saturation of the karst underground and extremely high rainfall in the wider hinterland of the ponor, water flows out from the Srđevići Ponor for a short time. This is the case when, due to intense rainfall, the piezometric line in the massif of the Bjelasnica and Baba mountains rises high above the elevation of Srđevići ponor inlet. A change of regime from ponor to spring also indicates limited drainage capacity of the Srđevići karst system. This is different from the Jasikovac-Vranjača ponor zone, whose

80

1

Natural Characteristics

Fig. 1.78 Dabarsko Polje in a flood, 1986 (Photo Milanović)

drainage capacity is far greater. Therefore, it is not wrong to consider Srđevići as a ponor and not an estavelle. The direct underground connection between Fatničko Polje and Trebišnjica springs is extraordinarily important for the operation of power plants in the HET system, first of all for operation of the Bileća Reservoir. Because of this, Srđevići Ponor has been equipped for monitoring since the first days of the hydrosystem operation. All the water that sinks in Malo Gatačko Polje flows as underground flow towards the Trebišnjica springs, either directly or, in a period of high water, as part of water that temporarily appears on the surface in Cerničko and Fatničko poljes. Only one, very small part of the water of Gatačko Polje does not belong to the Trebišnjica basin. That is the area in the very eastern a part of the polje, between Ljeljinački Ponor (Fig. 1.94) and Bobotovo cemetery. The waters that sink into these ponors flow towards the springs of Piva River (Sinjac Spring), presently submerged by Piva Reservoir.

Flooding of Veliko Gatačko Polje is a rare occurrence, while flooding of Small Gatačko Polje follows every wet period, with precipitation of an average annual level. The floods of Malo Gatačko Polje start when the flow of the Mušnica River is established along the sinkhole zone from Srđevići to Šabanov Ponor, in Little Kulsko field (Fig. 1.95). The elevation of this part of the polje is about 929 m and the concrete overflow in front of the Šabanov Ponor opening is at 924.90 m a.s.l., the lowest point of Malo Gatačko Polje. When floods in this part of the polje reach approximately 3 m, which is the elevation of the limestone pass (approx. 932 m a.s.l.), the overflow begins towards the ponor zone, the most significant of which are the Jasikovac and Vranjača ponors. Each of these ponors has additionalopenings on the different elevations: Jasikovac between 920 and 927 (Fig. 1.96) and Vranjača about 935 m. An increase in the flood level from 3 m to approximately 6 m results in the cumulative sinking capacity through the ponors to reache approximately 160 m3/s.

1.6 Karst Poljes

81

Fig. 1.79 Dabarsko Polje, Vrijeka Spring with water gauging station for measurement durin low water flow, 2009 (Photo by Milanović)

Flow of the Mušnica River usually varies from approximately 100 m3/s (97.2 m3/s, (16.11.1997) to 0.06 m3/s in a dry period of the year. In a flood period, the Mušnica river flow can increase enormously. In the flood 10/11.10.1975, the following flows were registered: Water Gauge Station (WGS) Klinje— 408 m3/s, WGS Mulja (Avtovac)—467 m3/s, and on the WGS Srđevići—600 m3/s. These flows caused flooding of the polje (Fig. 1.97). Measurements at seven precipitation stations in the area of Gatačko Polje showed rainfall from 144 mm to 160 mm in 8 h. Because the Mušnica River upstream of WGS Klinje has a torrential character, the flow grew enormously in a very short time. These flows caused flooding at the Šabanov Ponor area, 933.47 m above sea level. In the western part of Veliki Gatačko Polje, the altitude of the flood reached 938.8 m. It is important to note that a protective net was installed between the bridge at the level of the dam crest and the overflow structure, to prevent removal of juvenile fish from the reservoir. Torrential flows carried branches and silt and created an impervious plug at the overflow structure. Because of this, the water level in the reservoir rose very quickly by more than 2 m, the water flowed along the dam crest, knocked down a

downstream fence wall and demolished the bridge above the overflow structure (Fig. 1.98). This contributed to an increase of flooding, which registered at the downstream water measuring stations. In a very short time, the water flowed over the Avtovac–Stepen road and flooded Gatačko Polje. If the dam overflow had been in operational condition during the flood, the wave would certainly have been more extended, but the flood could not be avoided.

1.6.11 Nevesinjsko Polje This is the largest karst polje in East Herzegovina, with an area of 170 km2 of which 109 km2 is arable. It is inclined from the north (about 870 m above sea level) to the south, toward the lowest points in the area of the Biograd Ponor at an elevation of 799.90 m (Fig. 1.99). A huge depression formed by post-Eocene movements in the area of the current massif Trusina Mountain and Nevesinjsko Polje, the Promina formation is deposited above intensively karstified limestone paleo-relief. In the southeast part of the Nevesinjsko Polje, a very pronounced

82

1

Natural Characteristics

Fig. 1.80 Photo, Vrijeka River from discharge at the Vrijeka Spring (Vrelo Vrijeka) to the sinking into the Ponikva Ponor (1982) and graph of cumulative sinking (Photo Milanović)

paleo-depression with a deposit of the Promina formation is over 800 m thick. During the Neogene, in part of the polje (wider area Dubljanice), freshwater sediments with coal are deposited. At the same time, coal sediments are deposited in Mostar, Nevesinje and Gacko sedimentation rift. Due to intensely neotectonic movements, with an emphasized vertical component, the neogene basins, Nevesinjski and Gatački, are uplifted 1.500 m comparing by Mostar basin. The Promina formation consists of Paleogene sediments of the molasses type. The dominant lithological members are conglomerates. In the deeper parts, there are predominantly small and less rounded pieces of rudist limestone, ranging in size from a few millimeters to more than 1 m, with carbonate cement. There are also alveolinic-numulitic limestones but these are less represented. Pebbles and irregular pieces are cemented with carbonated and sandy cement. Above them are deposited thick masses of conglomerate that consist of pieces with an origin from the sediments of a different age, from Jurassic to Eocene. In this zone, pieces of eruptive rocks (gabbro and diabase) are often found. The final sequence consists of conglomerates with carbonate pebbles of uniform composition.

The area between Zovi Do and Biograd is composed of the Promina formation in which, except conglomerates, the marl layers are registered. Drilling in conglomerates of the Promina sediments in this area to the depth of 100 m revealed four separate zones of marl, with a total thickness of 44 m. Along the Odžak–Budisavlje line (borehole O-1) revealed a depth of 162 m, with six zones of marl, totalling 76 m thick. Geophysical investigative works established that carbonate paleo-relief of the depression in which the rapid deposition of these molasses took place has a distinctly uneven topographical nature (Aranđelović, 1976). In some parts, these depressions are deep (according to geoelectric sounding data), to an elevation of +50 m, as was the case below Ljeskovik and Grebak, while in the area of Žiljevo, a limestone ridge breaks out on the surface of the terrain. In most cases, these sediments lie concordant over the Eocene flysch and discordantly over older formations, but they have individual lateral borders that are undoubtedly tectonic. Subvertical to the vertical tectonic border separates the Promina conglomerate mass from the Velež Mountain carbonate massif. The position of this contact is confirmed by drilling (borehole N) in immediately nearby fault surfaces, at the foot of Mali Veleža, southwest of the Stupine area.

1.6 Karst Poljes

83

Fig. 1.81 Dabarsko Polje, Pribitu Spring, 2009 (Photo Milanović)

Given that the matrix of Promina deposits is made of carbonate rocks and that cemetation is also carbonate, it is logical that this mass is karstification prone. All forms typical for karst are found in these masses: lapies, sinkholes, ponors, shafts and caves. In the valley of Drežanjski creek, a dry cave was registered in the spring zone and two caves in the middle part of the creek bed, from which large amounts of water flow out during periods of precipitation. The very source of this flow has a typical karst “eye” and is formed in conglomerates. Two tapped springs in Nevesinjsko Polje (Jezdoš and Jedreš) represent typical karst phenomena in conglomerates. The Jezdoš cave channel was explored to a length of 48 m, while a channel of Jedreš explored to a length of 230 m. In conglomerates in the area of Grebak, upstream of the Biograd Ponor, a large number of ponors were found that are more than 100 m away from the Zalomka riverbed. All of them are hypsometrically significantly higher than the riverbed. Ponors and zones where water sinks are established in more places along the Zovidolka and Zalomka riverbeds.

In the polje itself, the hydrographic network is very scarce, with temporary streams in a period of precipitation and snow melting. More significant permanent streams are Alagovac and Dušila. In the summer period, their flows are very small, so it can be said that these are torrent flows. Alagovac is located in the northwestern part of the polje and sinks into the Ždrijelo Ponor. Dušila stream flows for about 5 km and sinks into the Babin (Babov) Ponor. According to B. Đerković (1966), the catchment area of Alagovac is 13 km2. For water supply for the town of Nevesinje on the Alagovac stream, a dam was constructed upstream from the Ždrijelo Ponor. The dam forms a reservoir, about 3 km in length, 200 to 250 m width, and 8–10 m depth. In Nevesinjsko Polje, floodwater forms two temporary acumulations. One is formed in the northern part of the polje, and it is much smaller and a more rare occurrence than that which is formed in south, which acts as beforeponor retention for the Biograd Ponor.

84

1

Natural Characteristics

Fig. 1.82 Ponikva Ponor in Dabarsko Polje, 1972 (Photo Milanović)

The most significant ponors through which the waters of the northern part of Nevesinjsko Polje are drained are Ždrijelo (825.76 m above sea level) and Babova Jama, along the western edge of the polje, at the contact with limestone massif of Velež Mountain and the Zlatac Ponor (828.99 m a.s.l.), close to the northeastern edge of the polje and close to the village of Donja Bijenja (Fig. 1.100). All water that sinks into these ponors discharge at the Buna Spring. Zlatac and Ždrijelo ponors are equipped with water measuring rods. In the area of Donja Bijenja, at the very foot of the dolomite massif of the Crvanj Mountain, there is atemporary spring, that is, a cave with water. The largest amount of water in Nevesinjsko Polje is brought by the temporary flow of the Zalomka River, with Drežanjka and Zovidolka tributaries. The Zalomka River enters the Nevesinjsko Polje near the village of Kifino. It flows near the edge of the polje and sinks in the Biograd Ponor (Fig. 1.101). All water which sinks into the Biograd Ponor flows toward the Bunica Spring. The Biograd Ponor is the largest ponor in East Herzegovina, with of swallowing capacity of over 110 m3/s (Fig. 1.102).

The connection between the Biograd Ponor and Bunica Spring is one of the most direct underground links in the karst of East Herzegovina. When 80 m3/s flows into the ponor, the velocity of the underground flow is more than 33.67 cm/s. The inflow into the Biograd Ponor with a free water surface is aup to an elevation of approximately 805 m. With an increase in the level of floodwater, the karst system comes under pressure. In an extreme situation with heavy rainfall, the capacity of the Biograd Ponor is not enough to receive all the water of Zalomka flow, and a smaller part of the Nevesinjsko Polje upstream of the ponor becomes flooded. Because it has an elevation of approximately 815 m, water is still in the riverbed of the Zalomka, flooding only when the water level rises above this elevation. In these circumstances, average duration of the flood is 37 days. When the flood reaches an elevation of about 820 m, it begins to overflow towards the valley of Radimlja, i.e., in the direction of Bregava. In that period, the groundwater levels are close to or at the level of the Zalomka River. In this case, some estavelles are also active, and seepage along the riverbed is limited.

1.6 Karst Poljes

Fig. 1.83 Dabarsko Polje. Underground flow connections of sinking water in Dabarsko Polje (a) Layout and (b) Cross-section. 1. Permanent spring, 2. Temporary spring (estavelle), 3. Ponor, 4. Temporary river

85

flow, 5. Permanent river flow, 6. Underground flow connection, 7. Watershed of Dabarsko Polje catchment area (Milanović, 2018)

86

1

Natural Characteristics

Fig. 1.84 Area of Cerničko Polje—Meka Gruda. 1. Boreholes, 2. Spring with huge discharge fluctuation, 3. Large ponor, 4. Ponor, 5. Group of near ponors, 6. Shaft, 7. Cave (Milanović, 1980)

Runoff from this part of the Nevesinjsko Polje consists of the swallowing capacity of the Biograd Ponor and, in very extreme cases, on additional overflow, toward the Radimlja valley. The level of the largest recorded flood, which occurred on November 20 and 21, 1934, was 838.20 m above sea level (Fig. 1.103). The depth of the floodwater in the area of the Biograd Ponor was 38.30 m. Water sinks in the Biograd Ponor 210 days per year on average. Except water that sinks directly into the Biograd Ponor, the waters of a smaller part of the basin on Trusina Mountain (uvala Krupac) flows toward Bunica Spring. All other waters that sink along the beds of Zalomka and Zovidolka ponors, including direct infiltration in the vast Nevesinjsko Polje, flows toward the Buna Spring. The Biograd karst channel was explored by cave-diving to a

depth of 140 m (Sketch of the investigated channels is presented in Sect. 3.1.8). A part of the water sinks into the riverbed of the Zalomka River between the village of Kifino and Biograd Ponor. These waters flow through the limestone ridge under the polje (so-called ‘Žiljevo limestone ridge’) and discharges in the Buna Spring. Nevesinjsko Polje is characterized by extreme amplitudes of underground water fluctuation. In piezometeric boreholes (Ž boreholes) in the area of the Žiljevo limestone ridge, the registered amplitudes of underground water ranges between 280 and 320 m (Fig. 1.104). It is possible that minimal groundwater levels are deeper because some measured values are on the very bottom of the borehole and the ground water level is probably false.

1.6 Karst Poljes

87

Fig. 1.85 Cerničko Polje, including position of local anticline structure. Google Earth, supplemented in 2018

1.6.12 Lukavačko Polje Lukavačko Polje is situated at an elevation of 880 m. The surface area of this polje is about 2.5 km2 (Fig. 1.105). The lowest point towards which the polje waters are drained is the Mill Ponor, at an elevation of 852.30 m. The majority of the polje is formed in Promina sediments and partly in Eocene flysch. Part of the eastern edge of the polje is built by

Cretaceous (Senonian) limestone, in which ponors are formed. In the polje, a few smaller springs (Pištet and Ljubica) are registered, and two near the village of Upper Lukavac are tapped. Lukavačko Polje is connected with Nevesinjsko Polje by the valley of the Zovidolka River. Between the poljes and the Zovidolka Spring (the Jama siphon spring near the village of Udbine) stretches a dry valley, the former drainage valley of

Fig. 1.86 Cerničko Polje. (a) layout (b) cross-section. 1. Karstified limestone, 2. Eocene flysch, 3. Spring with high discharge difference, 4. Ponor, 5. Surface flow, 6. Reverse fault (Milanović, 1979)

88

1

Natural Characteristics

Fig. 1.87 Cerničko Polje. Ključka River from spring Vilina cave (Fairy cave) to the end ponor, 1975 (Photo by Milanović, 1975)

Fig. 1.88 Cerničko Polje. (a) Spring Fairy cave, 1975 (b) Ponor Ključka River, 2016 (Photos P. Milanović)

1.6 Karst Poljes

89

Fig. 1.89 Cerničko Polje. Jasovica Ponor zone along the southern perimeter of the polje 1973 (Photo by Milanović)

Lukavačko Polje. The polje is drained through the mentioned ponors. By tracer investigation, it is established that water from the Mill Ponor flows toward the permanent Vrijeka Spring and temporary Susica Spring, on the northern rim of Dabarsko Polje. With these investigations, it is established that there is a watershed in the area of Lukavačko Polje, between Bregava catchment area and Buna-Bunica springs. Zone.

1.6.13 Slato Polje The altitude of Slato Polje ranges between 1060 and 1020 m, and the surface is about 1.5 km2 (Fig. 1.105). The lowest point of the polje is Mill Ponor, situated on the south rim of the polje about 1000 m a.s.l. The polje is formed along the regional reverse structure in Eocene flysch sediments and partly in Promina conglomerates. This is the same reverse fault on which the Cerničko Polje was formed. The southern edge of the polje is built by Cretaceous limestone, and ponors

are formed in them, through which the polje is drained. In a period of great precipitation, the field is periodically flooded. Slato Polje is connected with Nevesinjsko Polje and the Zalomka valley by a narrow dry canyon, which is cut in Promina conglomerates. In the lower part of this valley is the Drežanj creek. Several caves in conglomerates were registered along the creek, through which water flows into thecreek in a period of precipitation. The flood waters of Slato Polje plunge through two sinkholes, one of which is the more significant Mlinica (Mill) Ponor. These waters flow towards the Zovidolka valley. It is estimated that about 80% of this water appears at the Jama Spring and the rest discharges at temporary springs along the Zovidolka riverbed, downstream from the Jama, in a length of approximately 3.5 km. These are the springs of Pećina, Vrioci, Brusac and Milosava. About half a kilometer downstream, a part of these waters sinks into the Ćetanuša estavelle, situated in the Zovidolka riverbed, and continues as underground flow toward the Buna Spring.

90

1

Natural Characteristics

Fig. 1.90 Cerničko Polje. Beginning of flood, October 1975 (Photo P. Milanović)

1.6.14 Trusinsko Polje The Trusinsko Polje is located north of the northwestern very end part of Dabarsko Polje (Podkom area) at an altitude between 850 and 870 m. It is a small polje, about 2.5 km long and between 0.2 and 0.5 km wide (Figs. 1.106 and 1.107). The longer axis of the polje has a dinaric direction. The polje is cut in alveoline-nummulitic limestone, and the ultimate eastern part in molasses so-called Promina series (conglomerates and sandstones with layers of marl). The area north of the Trusinsko Polje consists of karstified limestone of Cretaceous age that is divided into two blocks along the regional reverse fault with Dinaric strike. It is the same fault along which Fatničko and Dabarsko Poljes were created. Along this fault, the Krupac uvala was formed. By tracer test of the ponor in this uvala, it is established that sinking water flows toward the Bunica Spring. Temporary flow of Opačica River can be divided on the upstream part into the Trusinsko Polje from the spring area to

the waterfall above Podkom and the part through the Dabarsko Polje. The height of the waterfall is about 300 m. The waterfall is active during wet period of year, only. The spring zone is in Promina conglomerates. The flow is active along its entire length only during a period of rainfall. Downstream from the waterfall (the entrance of Opačica to Dabarsko poljes) the bed is cut into the sediments of Eocene flysch that consist mostly of marly component. Downstream of the inflow of the right tributary into the Opačica flow, the substratum beneath alluvial sediments is alveolinenummulitic limestone. Simultaneous hydrological measurements, which are done before the end of a wet period (10.4.2009, Ž. Zubac, HET) show that flow in the area of the spring zone (Q = 78 l/s) is twice as large as flow on the last downstream profile in Dabarsko Polje (Blace locality), near the bridge on the Berkovići—Stolac road, Q = 39 l/s. At some points, the Opačica flow downstream from the waterfall was only Q = 12 l/s, and after inflow of the right tributary (Podkom locality) 22 l/s was measured. This means that, in this part of the riverbed, part of the water from alluvial sediments drains.

1.6 Karst Poljes

91

Fig. 1.91 Gatačko Polje, including part of an open coal mine for the Gacko thermal power plant, 2016 (Photo by Milanović)

1.6.15 Konavosko Polje (Konavli) Konavli Polje is hypsometrically the lowest polje of this region, at 60 m above sea level, with an area of 48 km2 of which 42.2 km2 is arable land. It is formed along the front of the High Karst Overthrust. Under natural conditions, the lowest part of the polje along its southern edge is temporarily flooded. The northern rim and the bottom of Konavosko Polje consist of sediments of Eocene flysch over which Jurassic limestone is overthrusted. This is the area with the largest spreading of flysch sediments along the High Karst Overthrust. By depth, these sediments were put down under an elevation of 0.00 m The carbonate ridge between polje and sea, with a width of about 2 km, consists of Upper Cretaceous dolomites, including one narow zone of Cretaceous limestone along the seacoast. These dolomites are very much karstified. In the tunnel between polje and sea, with a length of 1.944 m, which serves as Konavosko Polje drainage, numerous caverns are found that are often filled with clayey material. A more detailed explanation of the problem of caverns along the route of this tunnel is given in Chap. 4. Alluvial sediments are deposited along the flow of the Ljuta River and Konavočica and Kopačica tributaries. There are developed river terraces along the valleys of these temporary rivers locally.

Konavoska Ljuta is the most significant spring in Konavosko Polje. The spring zone is located at the contact of Eocene flysch and the carbonate Mesozoic complex, at elevations between 80 and 90 m. The waters of a number of small springs form the Kopačica stream, which is a branch of the Ljuta River, with confluence close to the Jaz ponor zone, at the southern perimeter of the polje. After excavation of drainage tunnels, these ponor zones are reduced to a minimum.

1.6.16 Gradac Polje Gradac belongs to the group of smaller poljes of East Herzegovina, with an area of 2.3 km2 (Fig. 1.108). It is located at an altitude of 86 m above sea level. It is formed in Eocene limestone along the reverse fault that extends along the northern edge of the polje. The bottom is covered with a thin layer of arable soil, with local occurrences of limestone on the surface. There are no springs in the polje, nor permanent or temporary surface flows. The most significant karst form is Gradnica shaft. It is a vertical channel with a diameter of about 20 m and a depth of 85 m, which is close to sea level. The channel continues almost horizontal but is impassable because it ends in a siphonal lake. Floods in the polje are rare, approximately once every 10 years. It happens in periods of

92

1

Natural Characteristics

Fig. 1.92 Gatačko Polje. 1. Tapped spring, 2. Small permanent spring, 3. Small temporary spring, 4. Great ponor, 5. Ponor, 6. Water supply well, 7. Irrigation canals (mostly abandoned), 8. Quaternary sediments, 9. Flysch, 10. Neogene, 11. Jurassic limestone, 12. Triassic dolomites (Milanović, 2006)

huge precipitation when the water level in Gradnica rises up to the surface of the terrain. Floods are short-lived and the depth of floodwater in the polje is small. Local people associate flooding of the polje with a strong southern wind that, during periods of intense rainfall, blocks underground flows in the direction of the sea. By tracer test of the Međine Ponor (2.12.1972), a connection with springs at the Neretva valley was established. The largest amount of dye discharges in the Mlinište Spring (+2 m nm). Gradnica shaft is situated between a large sinking zone in Popovo Polje (225 m a.s.l.) and the spring zone along the Neretva valley (+2 m a.s.l). However, in spite of a large number of tracer tests, a link between Popovo Polje and Gradnica was registered only once, when dye was injected in the Ponikva Ponor. There is some weak indication of underground flow connection between Kaluđerov Ponor and Gradnica shaft, but it is not accepted as reliable.

1.7

Hutovo Blato

The wetland area of Hutovo Blato (Hutovo Mud) consists of two cryptodepressions (Svitava and Derane) between Čapljina and Metković, which are connected with each other and with the Neretva valley. The total surface of Hutovo Blato includes 7.411 ha, from which a constant water surface area spreads on 1402 ha and the wetland on 2150 ha (Dašković, 2009). The average level of the lakeswamp surface area fluctuates between 1 and 3 m a.s.l. The waters of Hutovo Blato belong to the Trebišnjica and Bregava basins, with a smaller part from its own catchment area. Surface inflow does not exist and outflow into the Neretva River takes place exclusively by the Krupa River. The first ideas about reclamation of Hutovo Blato date back to 1910, and the drainage works started in 1925. After World War II, works were intensified. In the period

1.7 Hutovo Blato

93

Fig. 1.93 Gatačko Polje—Srđevići gorge. Srđevići Ponor (estavelle), 2016 (Photo by Milanović)

1955–1959, more than 200 shallow geological boreholes were drilled, and from 1960 to 1962 an additional 60 boreholes were drilled. For the needs of reclamation of the Hutovo Blato, extensive hydrogeological investigations were organized in 1965 (Geoistraživanja—Elektrosonda, Zagreb, A. Šarin). After that, the idea of complete reclamation of the entire Hutovo Blato was abandoned. The area west of the Krupa River, (so-called Višićka cassette), which is protected by an embankment, has been brought to agricultural production. According to geological characteristics, the cryptodepressions of Hutovo Blato have lithostratigraphic and also structural characteristics of Dinaric karst (Fig. 1.109). Cretaceous sediments are the most represented stratigraphic unit, mainly karstified limestones which prevail in the catchment area. Paleogene sediments (Paleocene/Eocene and Eocene) are in second place, in terms of representation.

Long zones of nummulitic limestone lie down discordantly across Cretaceous limestone. Northeast blocks of Cretaceous limestone are overthrusted across Eocene, along the reverse tectonic contact of the Dinaric strike. Locally, along this contact, are inserted zones of Eocene flysch. The entire cryptodepression of Derane is formed in a monoclinal structure of Cretaceous limestone. The Svitava cryptodepression is formed in predominantly Paleogene limestones, except at the southwest rim (between Desilo and Doljani) which consists of Upper Cretaceous limestone. Since the Ostrovo ridge separates Hutovo Blato into two separate geomorphological units, the possibility of their hydrogeological connection through the ridge was analyzed. In the western part of Ostrovo, two boreholes were drilled, with a depth of 30 and 35 m. By monitoring the water regime in them, it was determined that a hydrogeological connection between Svitava and Derane depressions through the Ostrovo does not exist.

94

1

Natural Characteristics

Fig. 1.94 Gatačko Polje. Ljeljinački Ponor 1963 (Photo Milanović)

Both depressions are filled with neogene sediments: clay, peat, limestone blocks in clayey mass and sandy clay at the bottom. The total thickness of these sediments in the Svitava depression is estimated at more than 100 m. According to the results of geophysical investigations, the depth of the Neogene sediments is locally greater than 150 m. Only the upper 20–25 m were investigated with boreholes. In that area the percentage of the clay component varies between 10% and 80% (Simić, 1975). Thickness of peat in both depressions varies between 10 and 20 m. According to the results of geophysical sounding (Geofizika, Zagreb, 1964) the thickness of peat in the central part of the Derane depression is at least 64 m. Most probably, formation of peat started at the beginning of the Quaternary and that process lasts to today. The presence of partially carbonized oak trunks was confirmed by several investigative boreholes. Clay sediments contain different percentages of sandy fractions and represent the youngest member of the Quaternary. The basic structural features are linear reverse faults in the Dinaric strike whose continuity is often disturbed by

numerous ruptures that are at a certain angle to the Dinaric direction. Determining the catchment area of Hutovo Blato is exceptionally complicated. Inflow takes place through numerous springs along the edges of both depressions but also through numerous lacustrine springs detected at the bottom of Derane Lake. Toward the north the watershed can be declared the Bregava River and toward the south it is the Trebišnjica River, i.e., part of Popovo Polje downstream from Čavaš (Fig. 1.110). The water divide towards Ljubinjsko Polje is determined approximately. The approximate surface of the catchment area is 420 km2, including the area of Hutovo Blato itself. This area, together with Ostrovo, is estimated at 40 km2. The most significant inflows in the Derane depression belong to sinking water along the Bregava riverbed. Probably a negligible part of the water that sinks into Dabarsko Polje flows directly towards the Derane depression. However, it is not proven. About 40 m3/s of water of Popovo Polje, at a flood level of 4 m, flows towards Hutovo Blato. When the

1.7 Hutovo Blato

Fig. 1.95 Malo (Small) Gatačko Polje. Flood in front of Šabanov Ponor, 1972 (Photo Milanović)

Fig. 1.96 Malo Gatačko Polje. (a) Šabanov Ponor (b) One of the inlets of Jasikovac ponor zone, 2016 (photos Milanović)

95

96

1

Natural Characteristics

Fig. 1.97 Gatačko Polje. Flood on 13.10.1975

Fig. 1.98 Gatačko Polje. After flood, 1975. Overflow structure at Klinje Dam without bridge, and demolished downstream fence wall along the dam crest

flood level reaches 8 m in the direction of Hutovo Blato, about 120 m3/s of sinking water flows. Active karst channels were found during the excavation for the machine hall of RPP Čapljina, at elevations of 30 to 40 m below zero. Undoubtedly, karstification developed until the deepest parts of these cryptodepressions.

During periods of heavy rainfall, water discharges from a number of places along the southwest rim of the Svitava depression. This creates a spring zone several kilometers long. Under natural conditions (before construction of the embankment along this rim), the water level in the Svitava depression fluctuated from 0.5 m a.s.l. to 5.8 m a.s.l.

1.7 Hutovo Blato

97

Fig. 1.99 Nevesinjsko Polje. 1. Cave with temporary spring, 2. Large ponor, 3. Ponor, 4. Small discharge spring, 5. Large permanent spring, 6. Temporary river flow, 7. Established underground link (P. Milanović, 1980)

Based on long-term hydrological measurements, it was established that, during periods of extremely large water flow of the Neretva River, the Krupa River temporarily changes direction and flows opposite (upstream) towards Derane Lake. In these circumstances, Hutovo Blato becomes natural retention (Barbalić, 1978). Based on simultaneous hydrological data from the Neretva—Škrka—Derane Lake gauging stations, Šarin et al., (1965) concluded that the influence of flood waters in Popovo Polje on Derane Lake is insignificant. At the same time, the large waters of the Neretva flow have a direct

influence (“probably via influence of downstream flow of Bregava River”). As one of the last wetland habitats in Europe of international importance, Hutovo Blato was included in the Ramsar list in 1971. Because of its exceptional richness with ichthyofauna, ornithofauna and flora, and the role this part of the Dinarides has on bird migration, as well as being an area with important touristic potential, Hutovo Blato received the status of a nature park (1995). It is also included in the WWF project for the Mediterranean area (Mateljak, 2009). More detail about the springs of Hutovo Blato in Chap. 2, Sect. 2.3.2.

98

1

Natural Characteristics

Fig. 1.100 Northern part of Nevesinjsko Polje. 1. Investigation borehole, 2. Ponor with swallowing capacity over 1 m3/s, 3. Ponor, 4. Permanent spring, 5. Temporary spring, 6. Small permanent spring

Fig. 1.101 Biograd Ponor. Left—dry bed of Zalomka in front of the swallow hole, (Photo by Resner 1979). Right—entrance into the swallow hole, 1969 (Photo by Milanović)

Hutovo Blato Fig. 1.102 Nevesinjsko Polje. Sinking graph of Biograd Ponor (courtesy Energoprojekt, 2007)

99

100

1

Natural Characteristics

Fig. 1.103 Nevesinjsko Polje. Flood level carved at the rock on the road near the bridge over the Zalomka River. (Photo P. Milanović)

Fig. 1.104 Nevesinjsko Polje. Simplified cross-section Ž6—Buna Spring and groundwater fluctuation graph in boreholes situated inside the Žiljevo limestone ridge (Milanović, 2018)

Hutovo Blato

Fig. 1.105 Lukavačko Polje. Established underground links. Legend: Standard for Basic Geological Map (OGK, SFRY)

101

102

Fig. 1.106 (a) Trusinsko Polje (b) Waterfall between Trusinsko and Dabarsko Polje in the Podkom area

Fig. 1.107 Trusinsko Polje. Geological sketch. 1. Molasse (Promina), 2. Limestone with alveolines and nummulites, 3. Flysch, 4. Cretaceous karstified limestone, 5. Ponor, 6. Temporary flow of Opačica River, 7. Temporary spring, 8. Elevation, 9. Scree

1

Natural Characteristics

Hutovo Blato

Fig. 1.108 Gradac Polje, 1970. (Photo Milanović)

103

Fig. 1.109 Hutovo Blato, geological map. Taken from Basic Geological Map, SFRY, Sheet Metković, Institute for Geological Investigations, Sarajevo, 1958–1971

104 1 Natural Characteristics

Hutovo Blato

Fig. 1.110 Hutovo Blato. Topography map with underground water connections (Milanović, 2009)

105

106

References Absolon, K. (1916a). Z vyskumnych cest po Krasech Balkan. Zlata Praha, 4, Roč. 33. Prag. Absolon, K. (1916b). Vysledky Vyskumnych po Balkane. Časopis Morav. Mus. Zemsk, XV,2, Brno, pp. 245–249. Absolon, K. (1932). Die unterirdische Flüsse Ombla und Buna. Vprtag am 23.II.1932. Roterdam. Tijdoschr. v.h. Kon.Ned. Handrijksk. Genootsch.Leiden, 2 Reihe, 49, 4.Roterdam. Aljinović, B., Prelogović, E., & Skoko, D. (1987). New data about deep geological structures and seismotectonic active zones in Yugoslavia. Croatian Geological Bulletin, 40, 255–263. Aranđelović, D. (1970). Geophysics in civil engineerig. Bulletin of Institute for geological and geopysical investigations (Geozavod), X/XI, Ser. C, Beograd. Aranđelović, D. (1976). Geophysics in Karst. Special edition, Institute for Geology and Geophysics, Belgrade. Aranđelović, D. (1977). Report on geoelectrical investigations at area of PP Dabar. Documentation of HET-Trebinje. In Serbian. Aranđelović, D., Milanović, P., Filip, A., & Ramljak, P. (1976). Identification of space position of karst channels. In Proceedings. Karst Hydrology and Water Resources, Sarajevo. Arsovski, M., Mihajlov, V., Dojčinovski, D., & Cvijanović, D. (1982). Regional seismotectonic investigations to define seismic hazard. Report, IZIS. Skopje, North Macedonia. Avdagić, I. (1973). Experimental determination of parameters for water balans in karst. Institute for hydrotechnic, Civil Engineering Faculty in Sarajevo. In Serbian. Sarajevo. Avdagić, I. (1985). An aproach to determine outflow in karst hydrology systems. Scientific conference “Water and Karst”, Mostar, Bosnia and Herzegovina. Bagarić, I., Kovačina, N., & Milanović, P. (1980). Application of gasious tracers for detection of karst conduite space position. Publication:Naš krš. Vol. No 8, Sarajevo. Ballif P. 1896. Wasserbauten in Bosnien und der Hercegowina - I Teil, Meliorationsarbeiten und Cisternen im Karstgebilte. Printed in Vien. Barbalić, Z. (1976). Properties of water management systems of closed karst poljes. Proccedings of Yugoslav-U.S. symposium “Karst hydrology and water resources” 1975. Dubrovnik. Barbalić, Z. (1978). Efects of construction of daily reservoir “Svitava” on solution of water management problems in the area of the lower Neretva River. Proccedings: Conference on influence of man made reservoirs on environment. Yugoslav Commiittee of Lage Dams (JKVB). JKVB and HET. Trebinje. Behlilović, S. (1956). Geological properties of Trebišnjica River basen. Herald Geological. Sarajevo. Bojanić, L., & Ivičić, D. (1948). Hydrogeological Study of area Metković – Dubrovnik – Konavle. Geol. Institute for Geological Investigations. No. 186/84. Zagreb. Bonacci, O. (1995). Groundwater behaviour in karst: Example of the Ombla Spring, (Croatia). Journal of Hydrology, 165, 113–114. Bonacci, O. (2016). Hydrology analysis of turbidity ta springs in karst: Interpretation of measurement data at Ombla spring. In Croatian, Hrvatske vode, 24, 311–321. Boué, A. (1840). La Turkuie d'Europe III. Paris. Božičević, S. (1984). Morphology of the spring caves with the conglomerate of the Velež Mountain. Naš Krš, Buletin of Speleological Society, Vol. X, No. 16/17. Sarajevo. Buljan, R. (1999). Importance of structural model in design and protection of underground waters of Ombla Spring near Dubrovnik. Ph Disertation. Mining-Geological-Oil faculty, University in Zagreb. Buljan, R., & Prelogović, E. (1997). The significance of structural and geological relationship assesment in the construction of the Ombla underground Hydroelectric Power Plant. Minig-geological-oil Bulletin, 9, 17–22.

1

Natural Characteristics

Bušatlija, I. (1963). Some problems of hydrography and morphology of Nevesinjsko Polje and its perimeter. Third Yugoslav Speleological Congress. Sarajevo. Chollay, A., & Chabot, G. (1930). Notes de morphologie karstique du polje de Lika au Popovo (Vol. 39, pp. 270–285). Ann.de geographie. Cvijanović, D. (1982). Regional seismotectonic investigations to define seismic hazard. Dams and hydropovers at Upper Horizons of Trebišnjica catchment. Coauthor with Arsovski M., Mihailov V., & Dojčinovski D. IZIS, Skopje. North Macedonia. Cvijić, J. (1900). Karst poljes of Western Bosnia and Herzegovina. Herald of Serbian Royal Acad, In Serbian LIX (pp. 59–182). Cvijić, J. (1924). Geomorphology I. Beograd. Cvijić, J. (1926). Geomorfology II. Beograd. Cvijić, J. (1950). Old uoutflows of Popovo Polje and hydrography zones in karst. Herald of Serbian Geographycal Society (reprint) No. 30, 1. Beograd. Čučković, S. (1978). Question of possibility to survive well known endem human fish in area of Hydrosystem Trebišnjica. Proccedings: Conference on influence of man made reservoirs on environment. In Serbian. Yugoslav Commiittee of Lage dams (JKVB). JKVB and HET. Daneš, J. (1905). Uvodi dolini Neretvy. Zbornik češke spločnosti zemčvidne, čis. 6,7,8 i9. Roč. 9. Prag. Daneš, J. (1906). La region de la Neretva inferieure. La Gegraphie, 13. Paris. Dašković, N. (2009). General properties of Hutovo Blato. EKO Herzegovina, No. 5. Publication on ecology, nature, environment, turism and sustainable development. In Croatian. Mostar – Čapljina. Dedić, N., & Ostojić, Đ. (1981). Design of protection of PK “Gračanica” - Gacko against ground water, Book 1, Technical proposals of design. Istitute for mining investigations. “IRI” - Tuzla. Dedijer, J. (1907). Some information about geological history of Neretva River. Herald of Nationsl Museum No. 19, Sarajevo. Đerković, B. (1966). Hydrogeological characteristics close area of Nevesinje. Herald Geological No. 11. Dragašević, T. (1983). Oil geologic exploration in the Montenegro offshore in Yugoslavia. Nafta, 34(7-8), 397–404. Groller, M. (1889). Das Popovo Polje in der Hercegovina. Mitth. d. geograph. Geselsch. Wien, pp. 80/89. Grund, A. (1910). Beträge zur Morphologie des Dinarischen Gebirges. Mit Abbildungen in Text, einer Tafel ubd 3 Karted. Leipzig; Berlin (translation, 1973, not published). Zagreb. Hadži, J. (1932). Contribution to the knowledge of Vjetrenica cave fauna. Serbian Royal Academy of Sciences, Belgrade. pp. 103–157. Havelka, V. (1931). Geologische Reiseskizzen aus der Hercegovina Südostbosnien und dem angrenzenden Teile der Crna Gora (Montenegros). III Teil. Glasnik Zemalj. Muz. BiH, 43 (1931), 1. Sarajevo. Herak, M. (1971). Tectogenetic approach of karst terraine classification. Krš Yugoslavie 9/4, Zagreb. Herak, M. (1986). A new concept of the Dinarides. Acta geol., JAZU, 16, 1–42. Zagreb. Croatia. Herak, M. (1991). Dinarides and mobilistic view to genesis and structures. Acta Geologica, 21(2), 35–117. Zagreb. Croatia. Hiljferding, A. (1873). Bosnia, Herzegovina and Old Serbia. (In Russian). Janković, M., & Gavrić, J. (1979). Strong earthquakes at vicinity of Grančarevo Dam. Report. Sarajevo. Not published. Karaman, S. (1953). Über Subterrane Amphipoden und Isopoden des Karstes von Dubrovnik und seines Hinterlandes. Acta Musei Macedonici Scientarum Naturalium, Vol. 1, 9, Skoplje. pp. 194– 216. Katzer, F. (1903). Das Popovo polje in Der Hercegovina. Globus, 83, 191–194. Katzer F. 1909. Karst und Karsthydrographie.

References Kovačina, S., & i Miljković, E. (2004). Development of Hydropower System in Trebišnjica river basin. Presentation: Round table, HET, Trebinje. Kusijanović, M. (1926). New caves in Dubrovnik comunity and area of Ston. Dubrovački list. In Croatian, 3(34), 1–2. Lazić, A. (1926). Underground hydrographic conection between Trebišnjica and Dubrovnik River. Herald of Serbian Geographic Society (12). Beograd. Lazić, A. (1927). Ponors and estavelles in Popovo Polje. Herald of Serbian Geographic Society, 13. Lazić, A. (1930). A few dry caves in herzegovinian karst. Herald Geographical Society, 16. Belgrade. pp. 151–156. Lazić, A. (1932). Trebišnjica Valley. Herald Geographical Society. 18. Belgrade. Lazić, A. (1933). Underground flows and hydrographic characteristics of Dabarsko and Fatničko polje. Serbian Royal Academy of sciences. 73. Belgrade. Lučić, I., & Sket, B. (2003). Vjetrenica – View in the soul of Earth (p. 322). Zagreb - Ravno. Lučić, I. (2019). Transformation of karst. History of knowledge of Dinaric karst - case study Popovo Polje. Monograph, Book (p. 679). In Croatian. Synopsis, Zagreb – Sarajevo. Malez, M. (1970). Caves in the region of Popovo polje and Dubrovnik. Carsus Iugoslaviae, Zagreb. Yugoslavia. Marković, B. (1966). Basic Geological map, Sheet Dubrovnik. Institut for geological and geophysical investigations, Beograd. Marković, M. (1973). Geomorphological evolution and newtectonic of Orjen Mountain. Doctor thesses. Mining-Geology Faculty, Beograd. Mateljak, Z. (2009). Conclusions and suggestions. Project devide water in catchments of Neretva and Trebišnjica. EKO Herzegovina, No. 5. Publication on ecology, nature, environment, turism and sustainable development. Mostar – Čapljina. Mikulec, S. (1972). Hydropower base of Neretva and Trebišnjica catchment area. Publication Energoinvest br. 4, Sarajevo. Milanović, P. (1971). An attenpt at defining the routes of the karst systam of Ponikva in Popovo Polje. Bulletin Scientifique, Section A – Tome 16(3–4). Milanović, P. (1975). Hydrogeology of Ombla Karst aquifer. Master theses. Mining – Geology Faculty, Hydrogeology department, University of Belgrade. Milanović, P. (1977). Hydrogeology of the Ombla Spring drainage area. Herald Geological 22. Sarajevo. pp. 187–255. Milanović, P. (1979). Karst hydrogeology and methods of investigation (302 p.). HE on Trebišnjica, Trebinje. Milanović, P. (1980). Posibility of aplication remote sensing in karst hydrogeology. Doctor theses, Mining - Geology Faculty, University in Belgrade. Milanović, P. (1981). Karst Hydrogeology. Water Resources Publication. Littleton, Colorado. Milanović, P. (2000). Geological Engineering in Karst. Zebra Publishing Ltd. 347. Milanović, P. (2004). Water without boundaries – water resources potential in deep karst of south-eastern Dinarides. 32nd International Geological Congress, Florence, Italy. Milanović, P. (2006). Karst of Eastern Herzegovina and Dubrovnik littoral. ASOS. Belgrade. Milanović, P. (2009). Study on hydrogeology of Nature Park Hutovo Blato. WWF European Policy Programme. Mostar. Milanović, P. (2018). Engineerin Karstology of dams and reservoirs (pp. 1–354). CRC Press. Milanović, P. (1992). Hydrogeological characteristics of geosyncline karst aquifers with an example of the Trebišnjica catchment. In H. Paloc & W. Back (Eds.), Hydrogeology of selected Karst regions. International Association of Hydrogeologists.

107 Milojević, S. (1927a). A few caves and shafts in Popovo Polje (Speleological investigations). Herald of Serbian Geographical Society in Belgrade, 13, 94–120. Milojević, S. (1927b). A few caves and shafts in Popovo Polje. Bulletin, Serbian Geograpical Society, No 13. Belgrade. Milojević, S. (1928). Speleological investigations in Popovo Polje and surrounding area 1925–1928. Herald of Serbian Geographical Society. 14. Belgrade. pp. 19–32. Milojević, S. (1935). Water storage in Vjetrenica Cave (Popovo Polje) and water supply the railroad from Gabela to Gruž. Trafici Overview, VI, 3, Beograd, pp. 91–96. Milojević, S. (1938). Questions on hydrographic function of Vjetrenica cave (Popovo Polje). Karst problems. Special edition Serbian Academy of Sciences, 123. Belgrade. pp. 160. Milojević, R. (1973). Coal Mine Gacko. Geological Investigations, Preliminary design. Geilogical Istitute of Bosnia and Hezegovina. Sarajevo. Milovanović, B. (1965). Epirogenic and orogenic dinamic in region of Outer Dinarides and problems of paleokarstification and geologic evolution of holokarst. Institut for Geological and geophysic investigations (Geozavod). Vol. IV/V. Mirković, M., et al. (1973). Basic Geological Map of Yugoslavia, Textual part. Sheets Gacko and Nikšić. Podgorica. Natević, Lj. (1970). Explanation for Basic Geological Map 1:100 000, SFRJ, Sheet Trebinje (In Serbian). Natević, L. J., & Petrović, V. (1970). Basic Geological map, Sheet Trebinje. Institut for geological and geophysical investigations, Beograd. Osipov, V. I., & Sokolov, V. N. (2013). Clays and their properties. Composition, structure, and formation of properties (p. 576). (In Russian) GEOS. Ostojić, Đ. (1980). Grout curtain for the protection of the open coal mine „Gračanica“ – Gacko against grondwater inflow. Geoinženjering Sarajevo. Pavičević, D., & Perreau, M. (2008). Advances in studies of the fauna of the Balkan Peninsula. Institute for Nature Conservation of Serbia. Monograph No. 22. Beograd. Petković, K. (1935). Contribution to knowledge of internal tectinic structures of autochthon terraine in Dubrovnik vicinity and its relation with overthrasted part. Geological Anales of Balkan Peninsula, Book 12, Second part, Beograd. Petković, K. (1958). Neue Erkentnisse uber den Bau der Dinariden. Jahrb.d.Geol. Bundes., 101, band. H.1, Wien. Petković, K. (1961). Overthrusts and imbricataded structures in tectonic formation of Montenegro and Herzegovina. Geological anales of Balkan Peninsula, XXVIII, Beograd. Petrović, B. (1965). Experimental plugging the estavelle Obod in Fatničko Polje. Documentation HET. Trebinje. Prelogović, E. (1975). New-tectinic map of Croatia. Croatian. Geol. Herald, 28, 97–108. Prelogović, E., & Kranjec, V. 1983. Geological development of the Adriatic Sea area. Croatian Primorski zbornik, 21, 387–405. Pretner, E. (1963). How to protect cave fauna in Vjetrenica near Zavala. III Yugoslav speleological congress, Sarajevo. pp. 169–174. Radovanović, M. (1929). Vjetrenica cave in Hercegovina. Morphologoc-hydrografic analisys. Bulletin Serbian Royal Academy, 68. Beograd. Rajić, V., Mojićević, M., & Papeš, J. (1971). Basic Geological Map of Yugoslavia, Textual part, Sheet Nevesinje, Sarajevo. Roksandić, M. (1970). Effects of the load by Reservoir on Seismic Activity. Proceedings of the Second Congress of the International Society for Rock Mechanic, Belgrade. Šarin, A., Radić, J., & i Škaberna, I. (1965). Hydrogeology of Hutovo blato area. Report. Geoistraživanja-Elektrosond, Zagreb. Croatia.

108 Šegota, T. (1982). Sea water level and vertical fluctuation of Adriatic Sea bottom from Riss-Würm interglaciation till today. Geology Herald, 35, 93. Sikošek, B. (1954). Tectoniks of Bileća – Trebinje region. Collection of Paper of Geological Institute “Jovan Žujović”, No.7, Belgrade. Simić, M. (1975). Some of results of complex geological investigation works in Svitava compensation storage basin, Reversible PP Čapljina. Proceedings. X YCOLD Congress, Cavtat, Croatia. Stevanović, Z., & Mijatović, B. (2005). Cvijić in karst. Serbian Academy of Science and Arts, Board on Karst and Speleology. Beograd. Stojić, P. (1980). Effects of reservoirs in karst areas on earthquakes. Hydrology papers, Colorado State University, Colorado, USA. Torbarov, K. (1976). Computation of water permeability and effective porosity in karst bz application recession curve. In Proceedings “Karst Hydrogeology and Water Resources”, Sarajevo.

1

Natural Characteristics

Vidović, M. (1961). Tectonoc of Adriatic littoral from Boka Kotorska to Neretva. Geological annals of Balcan Penincula. Book 28. Belgrade. pp. 143–155. Vukašinović, M., Vučinić, S., Metović, B., Šupić, V., Tešić, V., & Mamula, L. (1979). Definition of the main parameters of earthquake (15. 04. 1979) based on makroseismic data. Publication: Characteristics of earthquake that occured at 15. 04. 1979 year. Seizmologic Institute of Serbia, Belgrade and Seismologic Institute of Montenegro, Podgorica. Žibret, Ž., & Šimunić, Z. (1976). Fast method for definition outflow in closed karst poljes. Proceedings of Yugoslav-U.S. Symposium “Karst Hydrology and Water Resources” Dubrovnik, 1975. Zubčević, O. (1959). Speleological investigations in Velika pećina cave and Zvonuša schaft. Geographical overview, Book 3. Sarajevo. pp. 71–80. Zubčević, O. (1965). Trebišnjica River and valley. Doctor theses. Sarajevo.

2

Catchments, Surface Flows, Springs

Buna Spring

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. Milanović, Karst of East Herzegovina and Dubrovnik Littoral, Cave and Karst Systems of the World, https://doi.org/10.1007/978-3-031-28120-4_2

109

110

2 Catchments, Surface Flows Springs

2.1

Water Catchments and River Flows of East Herzegovina

2.1.1

General Characteristics

In the water catchments of East Herzegovina and Dubrovnik Littoral, water overflows, in the regime of underground and superficial streams, from higher (on the lower horizon) to the base of erosion—the sea coast and Neretva valley. Due to the specificity of the nature of karst and dominant underground circulation, in addition to water catchment areas, there are catchments of karst poljes and (or) karst springs. The largest and most important are the river catchments of Trebišnjica (including Mušnica), Zalomka, Bregava, and Buna, with its tributaries Bunica and Krupa. There are also numerous smaller, local catchment areas, which are emptied via springs along the Adriatic seacoast and the Neretva valley. Gatačko, Dabarsko, Ljubomirsko and Ljubinjsko Poljes have their own water catchments, as well as the northern part of Nevesinjsko Polje. Popovo, Trebinjsko, Mokro, Fatničko and Nevesinjsko Poljes (central and southern part) are hydrogeologically and hydrologically exceptionally complicated, because they simultaneously belong to catchments of large karst springs. Most of the large karst springs in this region belong to the type of rising springs, colloquially named siphonic springs: Ombla, Oko (Eye), Buna, Bunica, and Robinson springs, with the depth of the siphonic part of the channel down to 150+ m, relative to discharge elevation. In some cases, the parts of a water catchment area depend on hydrometeorological conditions, that is, on the current saturation of the karst aquifer. So, in natural conditions in a dry period, waters that belong to the Trebišnjica catchment area terminate exclusively on the seacoast (Ombla Spring). In this period, hydrological, as well as hydrogeological, connection with Neretva River valley does not exist. In a wet period of the year, particularly during flood conditions in lowest part of Popovo and Fatničko poljes, apartial and temporary connection between Trebišnjica and Neretva catchment are established. After the Trebišnjica riverbed was paved by concrete, to transfer water toward Reversible Power Plant Čapljina, conections between Trebišnjica and Neretva catchments becomes permanent. The terms karst water catchment and watershed, in the majority of cases, do not fit the exact definition as it is in non-karst terrains. While in non-karst terrains, the catchment area is clear for each square meter of terrain, conditionally speaking, such cases are very rare in geosynclinal karst. Watersheds are mostly underground, they are not aligned with the morphology of terrain, and their position is variable in time and space. It is difficult to define them perfectly correctly, even by increasing the extensive investigations.

Therefore, there are large differences in the assessment of most water catchments, in various studies and projects. Thus, for the catchments in which the influence of karst is relatively minor (Mušnica River until Srđevići Ponor), there are significant differences in estimates of surface by different authors: 200, 225 and 302 km2. There are similar differences in the case of the Zalomka catchment area, to the Biograd Ponor—from 474 to 544 km2; or Bune with its tributary Bunica—890–1100 km2. There are big differences in determination of the Trebišnjica springs catchment area, especially its eastern part. In order to reduce these differences, a large volume of investigative work is necessary, beginning with tracer tests; however, in most cases they are unacceptably expensive. The term watershed in this text means of watershed zone or zonal watersheds. The assessments of the catchment areas referred in this text are based on the results of tracer investigative works, as well as geological and morphological characteristics of terrain. Although one catchment area in karst can belong to just one karst aquifer, however, typically a karst catchment area includes several interconnected aquifers. Hydrogeologically, the connection of these aquifers is especially pronounced in a period of complete saturation of a zone with dynamic reserves. That is, a period when activities of bifurcation zones considerably increase. In a period when aquifers are in a regime of intensive depletion, this connection becomes weaker, and hypsometrically higher aquifers are exhausted faster, feeding the basic aquifer of the catchment area. Next to Trebišnjica the waters of East Herzegovina are divided between the watersheds of Zalomka, Bregava and Buna, with tributary Bunica. Inside these catchments a number of subcatchments with different hydrological characteristics exist. The most important river courses are: Trebišnjica with its tributary Sušica, Zalomka with tributaries Drežanjka and Zovidolka, Mušnica with its tributary Gračanica, Buna with its tributary Bunica, Bregava with its tributary Radimlja and the Krupa River. Of these flows, only Buna with Bunica and Krupa flow continuously along their entire length. Other streams partially dry up in a dry period of year. Trebišnjica (in natural conditions) dries up downstream of Trebinje; Bregava dries up downstream from Stolac and upstream from the Bitunje; Mušnica dries up downstream from Srđevići; and Zalomka dries up at the Crni Kuk area. Despite its name, the Dubrovnik River is, above all, a submerged river valley, with the characteristics of a fjord rather than a river flow. Permanent streams with very little flow in the dry season are: Gračanica in Gatačko Polje, Vrijeka in Dabarsko Polje, with a length of 2.5 km (Fig. 1.80), Ključka River in Cerničko Polje, which is 300 m long (Fig. 1.87), Sušica, tributary of Trebišnjica (upstream from Lastva village).

2.1 Water Catchments and River Flows of East Herzegovina

Temporary streams, with torrential character are: Ljuta, Kopačica and Konavočica in Konavosko Polje; Brova in Ljubomirsko Polje; Bukov stream in Ljubinjsko Polje; Obod in Fatničko Polje; Opačica in Dabarsko Polje; Radimlja near Stolac, Đeropa and Jugovićki stream near Fojnica (together they make the Zalomka River); and Gojkovića stream in Gatačko Polje (tributary of Mušnica). As a curiosity, the constant and shortest stream is located north of Ljubomirsko Polje. Water from the permanent spring Šćenica, after flowing for approximately 20 m, disappears in the ponor that is also called Šćenica. Bifurcation zones are also a specific feature of the karst hydrogeology of East Herzegovina. A large number of bifurcation zones are registered: the area of Čemerno (between the Trebišnjica and Neretva catchments); Rašćelica (between Gatačko Polje and Zalomka River); riverbed of Zalomka from Rilja village to the Biograd Ponor (between Buna and Bunice); upstream part of the dry valley of Radimlja and Zmijski creek (between Bunica and Bregava); part of Trebinjsko Polje around Pridvoraci (between Ombla and Zavrelje); and Popovo Polje (along the Trebišnjica riverbed to Ponikva); with the most pronounced bifurcation zones, Provalija—Doljašnica (between the sea coast at south, Hutovo Blato toward the north and Neretva valley toward the west) and the southwest rim of Fatničko Polje between catchments of Trebišnjica and Bregava. In most of the listed cases, the conditions for bifurcation exist in only in the wet period of the year when, in addition to total saturation of the aquifer, surface flows are also activated.

2.1.2

Regional Trebišnjica Water Catchment

The dominant catchment in the area of East Herzegovina is the regional Trebišnjica river catchment. The Trebišnjica spring zone consists of two close discharge points known as Bileća Springs near Bileće town (Dejan’s cave and Nikšić Spring) and the spring zone in the Čepelica valley. The water catchment of the Trebišnjica spring zone include area from the watersheds toward the Black Sea catchment area (Čemerno, 1293 m above sea level—Lebršnik 1985 m a.s. l.) to the extreme western part of Popovo Polje (220 m a.s.l.), including Ponikva Ponor. This extremely complex catchment area can be broken down into three parts: – part of the water catchment with concentrated discharge through the springs of Trebišnjica and Čepelica by the dominant underground flow (except for the Mušnica catchment, in which the flow takes place predominantly on the surface);

111

– intercatchments from the Trebišnjica to the Gorica (along the Zupci fault) with the most significant sub-catchments of the Sušica River, Oko Spring and Stara Mlinica (Old Mill), with dominant surface flow and without losses outside the catchment area; – Trebišnjica catchment downstream from the Zupci fault and Lastva anticline, which includes surface flow but also includes sinking along the riverbed and with exclusive underground runoff flows outside the catchment area, i.e., outside the catchments of Trebinjsko, Mokro and Popovo Poljes. The catchment of the Trebišnjica springs borders the Neretva catchment (directly or via the catchments of Bregava, Buna and Bunica), and the Drina and Zeta rivers. The waters of the downstream section of Trebišnjica spring partly flow through underground karst channels directly into the Adriatic Sea, and partly via Deransko Blato, Svitava depression and Neretva valley, into the Adriatic Sea. In the area of Orjen, there is a water divide with the catchment of Boka Kotorska Bay. On the basis of all investigative works performed to date, it has been estimated that under the most favorable hydrological and hydrogeological conditions, the catchment area of Trebišnjica springs amounts to about 1150 km2. Part of the catchment, between Gatačko Polje and Trebišnjica springs accounts for about 800 km2. The area of the catchment to the Lastva anticline, that is, to the dam site of the Grančarevo Dam, is 1361 km2, and to the Gorica Dam is 1576 km2. The surface area of the Trebišnjica River catchment, until the watersheds of the Adriatic catchment area, to the Ponikva Ponor at the very end of Popovo Polje is about 2351 km2. This is without the catchment of Mokro Polje, with an area of about 90 km2. Including Mokro Polje, the total catchment area is estimated at 2441 km2. As with the other calculations of catchment areas in karst, this information is subject to correction, probably with an increase.

2.1.3

Catchment Area of Trebišnjica Springs

The Trebišnjica springs catchment includes catchments of the Gatačko (Mušnica River), Cerničko and Fatničko poljes and the spacious area of Korita, Plana, Bijela Rudina, Somina, Crkvice and Rudine in Montenegro (Fig. 2.1). Of all the mentioned catchments, only the Mušnica watershed (water divide) can be accurately demarcated with neighboring catchments. The catchment area includes three local erosion bases (Gatačko, Cerničko and Fatničko Polje), with the three largest infiltration zones (Srđevići—Šabanov Ponor, the Ključka

112

Fig. 2.1 Trebišnjica catchment area including intercatchments between Trebišnjica Springs and Gorica Dam. 1. Large springs, 2. Important ponor, 3. Underground links, 4. Watersheds

River Ponor (Ključki Ponor), including ponors along the southern rim of Cerničko Polje, and Pasmica Ponor zone in Fatničko Polje). There are also the two largest springs, Vilina cave in Cerničko Polje and Obod in Fatničko Polje. The watershed of the northern part of the Trebišnjica catchment area, which is also a watershed between the Adriatic and Black Sea (and the watershed of the Gatačko Polje catchment) is located in Cretaceous Durmitor Flysch formation in the Čemerno—Lebršnik area, which is mostly orographic. Toward the west, the watershed with the Neretva spring zone is in the same geological formation—Cretaceous

2 Catchments, Surface Flows Springs

flysch. West of Čemerno, the watershed intersects the bifurcation zone where the temporary surface stream flows towards the spring zone of the Neretva River. Water that sinks along the stream flows in the opposite direction and discharges in the valley of the Vrba stream. This is confirmed by tracer test. The watershed continues to the southwest, over the pass near Rašćelica, which separates surface watersheds between Gatačko Polje and Zalomka River. By tracer test of the ponor at the spring zone of Đerope (Zalomka), it was established that, at a certain ground water level GWL, after sinking, the water flows in the opposite direction, toward Jezerine in Gatačko Polje. By tracer test of two ponors on the reverse contact of Lukovica—Gradina, a connection with the Obod Spring in Fatničko Polje was established. Along this contact (at an altitude of 930 m) stretches the watershed between catchments of Zalomka and Trebišnjica. The other parts of the water divide of the catchment of the Drina River, toward the catchments of Piva and Sutjeska rivers, were determined with satisfactory accuracy. A small eastern part of Gatačko Polje belongs to the Piva catchment, including part of the dry valley Krstac—Nikšić Polje (Ljeljinački Ponor-Dobrelji, Bobotovo cemetery and Dobra voda—Charađe). Part of the southern edge of the Fatničko Polje is a bifurcation zone, which complicates locating the water divide with enough accuracy. From this zone, the water flows towards the springs of Trebišnjica and Bregava. The lack of investigative works makes it difficult to identify the watershed, with Bregava in the area between Dabarsko—Ljubomirsko Polje, as well as in the direction of Popovo Polje. All theinvestigation works done to date show that the watershed toward the catchment areas of Bregava, Buna and Bunica are underground, zonal, and its position in a period of full aquifer saturation is locally changeable. Particularly interesting is determination of the water divide in the large bifurcation zone between the catchments of Trebišnjica and Bregave, south of Fatničko Polje. The question was the possibility of seepage from the Bileća Resevoir toward Bregava springs, whether the Bileća Reservoir is watertight or not. Numerous works such as tracing of underground flows, geological mapping, geophysical research and investigative boreholes, and monitoring of GWL in piezometers were performed to confirm the position of the watershed. After a few years of intensive investigations, the position of the underground wide watershed zone was confirmed (Fig. 1.69). The wide underground water divide is the high base of karstification south of Fatničko Polje, i.e., the zone of compact (not karstified) rock mass that plays the role of hydrogeological barrier and prevents the possibility of seepage from the Bileća Reservoir, at an elevation of 400.00 m, in the direction of Bregava Springs, at elevations between 100 and 130 m. Sinking

2.1 Water Catchments and River Flows of East Herzegovina

waters from the Pasmica Ponor zone flow exclusively towards Trebišnjica springs, and the waters that sink in the estevelle zone along the edge of Fatničko Polje flow in both directions, towards the springs of Trebišnjica and Bregave. Dye testing of estavelle E-4, at an elevation of 471 m, established that there is a connection with Bregava Springs (Suhavić and Bitunja) and Trebišnjica springs (Bileća Springs and Čepelica Springs). The dyeing was done at a water level of 8.09 m at the Pasmica Ponor gauging station. Water which sinks into the estavelle at the northwest polje rim flows only in the direction of the springs of Bregava. This is confirmed by five different colored lycopodium spores simultaneously injected into five estavelles when they were in a swallowing regime. The width of this watershed zone is larger than 1 km. It is roughly estimated that between 10 and 15% of flood water flows from Fatničko Polje towards the Bregava River. The water regime and its catchment in the area of these watersheds is complicated by temporary discharge of water from Pasmica Ponor. The bifurcation area close to piezometer F-1 is the approximate border of Trebišnjica and Bregava catchments, south of Fatničko Polje. The most sensitive problem is determination of the eastern border of the catchment area, in the direction of the catchments of the Zeta River and Adriatic coast. A part of the Trebišnjica catchment, which borders the Adriatic coast catchments, is dismembered on the catchments of Nikšić Springs—the left side of the Bileća Reservoir, the Sušica subcatchment, and the Oko Spring subcatchment. The position of the water divide of Nikšić Spring with the catchment of the Zeta River and Montenegrin coast is approximate. Theoretically possible erosion bases with an impact on this area, which includes Somina and Njegoš mountains, are: – Trebišnjica Springs (Nikšić Spring, 325 m a.s.l.) – the left reservoir bank from Bileća Spring to the Grančarevo dam site – western rim of Nikšić Polje (Slansko Oko Qmax > 100 m3/s, 602 m a.s.l.) – valley of the Zeta River (Svinjička vrela, ~50 m a.s.l.) – sea level (Risan Bay) The only underground connection that has been determined by tracer works is the connection between the eastern part of Cernica Polje with Nikšić Spring. Other investigations through application of tracers in this area (toward Nikšić Polje) have not been done. Trepačka and Tupanjska springs on the slopes of Njegoš Mountain are located at heights of over 950 m above sea level. A connection with Svinjički springs was established by a dye test of the Trepački Ponor (Radulović, 2000). Morphological remains of the dry valley, G. Crkvice—D. Crkvice—Ubla, indicate the existence of a

113

pre-karst fluvial network and the probable existence of pre-Pleistocene tributaries of Trebišnjica along this valley. It is to be expected that, along this valley, karst channels are formed, towards the Bileća Springs. This is why the boundary of the Trebišnjica catchment in that areashifted to the east, approximately determined on the basis of geological and geomorphological features.

2.1.4

Mušnica River with Gračanica Tributary

The Mušnica River belongs to the Trebišnjica catchment area. With its tributaries Gračanica and Gojkovića (Žarović stream), it is the main surface drainage system in Gatačko Polje. The Mušnica River is formed by the streams Vrba, Ulinje (Dramešina) and Jasenice, and the flow ends in the ponor area of Malo Gatačko Polje, which extends from Srđevići Ponor to the Šabanov Ponor (Figs. 1.92 and 2.2). The Vrba Dam was built on the Vrba stream; downstream of the dam, on the most upstream part of Mušnica flow, is the Klinje Dam. Flows are controlled at the water gauging stations— Klinje, Avtovac (Mulja) and Srđevići. The surface area of the Mušnica catchment to the water gauge station WGS Klinje is 65 km2; to the WGS Mulja is 110 km2, and to the WGS Srđevići is 302 km2. The largest flows at these stations were measured during the great flood on October 13, 1975. More detailed data of this flood is presented in Chap. 1 (Figs. 1.97 and 1.98). Minimum flows were registered in the period between November 9 and 12, 1962. WGS Mulja in Avtovac—Qmin = 0.20–0.050 m3/s (Fig. 2.3b) WGS Srđevići—Qmin = 0.13 m3/s The Gračanica River Spring, Vratlo, is located north of Gacko, under the Živanj Mountain, at an elevation of 1.231 m (Fig. 2.4). The catchment area of the Gračanica River to the water gauging station in the village of Gračanica is 42.5 km2 (to the bridge 45.0 km2). WGS Gračanica—Fig. 2.3. The maximum flow was registered in the period of the already-mentioned flood (1975): – Qmax = 154 m3/s, a – Qmin = 0.05 m3/s (middle average flow in November 1962) In 1971, along the course of the Gračanica River, the potential dam sites Bahori and Kravarevo were geologically mapped. Mapping included the entire catchment area, particularly the reservoir area. Preparation of the geological map was carried out with the aim of considering the possibility of

114

2 Catchments, Surface Flows Springs

Fig. 2.2 Gatačko Polje. (a) Mušnica River at the entrance of Malo Gatačko Polje near Srđevići Ponor, (b) Malo (Small) Gatačko Polje, 2021 (Photos Milanović)

Fig. 2.3 Gatačko Polje (a) Weir Gračanica (b) Weir Mulja (Avtovac), (Photos Milanović)

transferring part of the water from Gatačko Polje to the future Zalomka reservoir through the tunnel and lateral canal (gravitational), which would avoid the expenditure of energy to convey water by pumping.

2.1.5

Trebišnjica Springs: General Data

The flow of the Trebišnjica River is created by discharge at two spring zones—permanent Bileća Springs and temporary Čepelica Springs. Bileća Springs consist of two discharge places beneath the Bileća urban area—the Dejan’s caves and Nikšić Spring (Fig. 2.5 and 2.6). Čepelica Springs, below Mirilovići village, consists of several springs, the largest of which are Čepo and Vrelina. Their flow is controlled on WGS Bridge 0–324.03 m a.s.l. Discharge of Bileća Springs is much higher than Čepelica Springs.

The spring zones of Bileća Springs are created in Upper Cretaceous limestone. In the lower parts of the spring, the rock mass consists of a significant mass of dolomites. Using hydrogeological investigation boreholes and geophysical geoelectrical sounding and mapping in the hinterland of the spring (area of Bilećko Polje), it was determined that karstification did not affect the rock mass below an elevation of approximately 300 m (Aranđelović 1966). Above this level, next to the karst channels, there are identified zones whose porosity reaches 10%. This percentage noticeably overcomes overall aquifer porosity, which is less than 2%. But, despite these data, the possibility of the existence of karst channels under the level of the base of karstification should not be excluded. However, they are very rare, with limited permeability. The discharge of Bileća Springs is controlled at WGS Bileća 0–324.26 m above sea level.

2.1 Water Catchments and River Flows of East Herzegovina

115

Fig. 2.4 Gatačko Polje. (a) Gračanica Spring, Vratlo (2016), (b) Canyon section of Gračanica River (1971), (Photos Milanović)

The overflow threshold of Dejan’s cave is located at an altitude of 325.2 m. The opening of the cave is 4 m wide and 6.5 m high (Fig. 2.7a). In natural conditions during summer, discharge from the cave dries up and a flow of approximately 2 m3/s was formed from the outflow eye, about 150 m downstream. This indicates that there are probably channels with the shape of a shallow siphon. Dejan’s cave is the final part of the branched system of karst channels with large flow capacity. On the basis of data collected during speleological investigation, which were carried out before the spring was submerged, it was determined that the karst channels of Dejan’s cave are almost horizontal. Around 510 m of channels were speleologically investigated, Petrović (1955) (Fig. 2.7). The Nikšić Spring (325 m above sea level) is located on the left bank, approximately 400 m downstream from Dejan’s cave. Under natural conditions, the discharge of Bileća Springs ranges widely, from Qmin = 0.6 m3/s (20.10.1947) up to Qmax > 400 m3/s. Downstream from Dejan’s cave, on the left bank and before the Nikšić Spring, there are three ponors into which 50 l/s sinks in a dry perod. The Bileća Reservoir was formed through construction of the Grančarevo Dam. The reservoir submerged the springs of Trebišnjica with a 75 m column of water. Despite such deep

water, during large discharge from Dejan’s cave, a large circular indication of sublacustrine discharge is visible on the surface of the reservoir (Fig. 2.8).

2.1.6

Reconstruction of Trebišnjica Karst Aquifer Evolution Process

The evolution of the Trebišnjica karst aquifer is a consequence of a complex tectonic-erosive process. In a period of fluvial erosion, the surface runoff from Gatačko Polje was guided west, through the valley of the present Zalomka River and east, through the Krstac—Duga dry valley. The destruction of this surface drainage system was especially intensive in the Oligocene-Miocene period. This period was characterized by intense folding of terrain. In the post-Miocene period, new tectonic movements occurred, with a dominant transversal component, which demolished the homogeneity of hydrogeologically significant structures in the dinaric direction. These movements and transverse faults have a key role in predisposing the development of new erosive cycles. The fluvial process was replaced by the karst process. Transversal fractures connect by the shortest way, by stepwise erosion base levels, and the intensity of the karstification process suddenly increases with rising northern blocks.

116

2 Catchments, Surface Flows Springs

Fig. 2.5 Bileća Springs. (a) Panoramic view before 1950. Authors unknown (b) From publication “Hydrosystem Trebišnjica” (1967)

The Neogene sedimentation trench of Gatačko Polje loses its surface drainage waterways and begins to work like a local erosive base. Evolution of this section of the karst aquifer takes place in two directions—towards the springs of Piva and south, in the direction of Fatničko and Bilećko Poljes, which is contrary to previous directions of surface flows. Under the influence of these erosive bases, two independent infiltration areas are created: 1. Malo Gatačko Polje, with the most important ponors being Jasikovac, Vranjača and Srđevići 2. Ponor zone of the eastern part of Gatačko Polje, from the Ljeljinački Ponor to the Bobotovo cemeteries and Dobra voda-Čarađe (Piva River catchment area) In spite of considerable destruction by transverse tectonics, a thin flysch barrier along the reverse fault represents a barrier

whose conditions support the formation of a concentrated discharge zone in Cerničko Polje (Fig. 2.9a). This flysch barrier was formed by the uplift of the Bjelasnica anticline, in the first phase of evolution. New infiltration zones are created here, with new karst channels of high permeability. They are predisposed by transversal tectonics, and discharging zones by spatial position of flysch barriers along the reverse structure, Fatničko Polje—Plana. By forming concentrated infiltration zones in the wider area of Pasmica, there is an increased intensity in the process of origin of a new independent karst aquifer. Because of adjustments to the current level of discharge in Trebišnjica springs, three separate karst aquifers between Gatačko Polje and Trebišnjica springs lose independence. The karst process captures rocky masses under hanging barriers and mutually connects these aquifers, so that a unique karst aquifer is

2.1 Water Catchments and River Flows of East Herzegovina

117

Fig. 2.6 Trebišnjica Spring zones before submergence, 1966 (Photos Aranđelović)

formed, which is deplanted through the Trebišnjica springs (Fig. 2.9b). Activity of the karst process downstream from the Trebišnjica Springs is prevented by the position of the dolomite core of the Lastva anticline. The directions of karstification were blocked toward the downstream erosion bases, first of all, toward the erosion base level of the Adriatic Sea.

2.1.7

Hydrogeological Characteristics of Trebišnjica Spring Aquifer

In the catchment area of Trebišnjica springs, three local erosion base levels dominate, with huge infiltration capacity and a tectonic, that is, hydrogeological ‘knot’ in the area of Plana (area of borehole PB-1), wherea few regional fault zones merge. Through that knot passes the longest

118

2 Catchments, Surface Flows Springs

Fig. 2.7 Dejan’s cave spring. (a) Entrance into the cave (Photo by Milanović 1983), 1. Water, 2. Bridge in front of cave (cave map Petrović, 1955)

Fig. 2.8 Trebišnjica springs. (a) Dejan’s cave (Photo Milanović, 1983), (b) Circle above Dejan’s Cave indicating huge sublacustrine discharge (2006)

2.1 Water Catchments and River Flows of East Herzegovina

Fig. 2.9 Karst aquifer transformation, between Gatačko Polje (I) and Trebišnjica Springs (IV), 1. Underground flows of separated aquifers, 2. Underground flows of united aquifer, 3. Groundwater level in maximum, 4. Compact limestone, 5. Permanent surface flow, 6. Temporary surface flow, 7. Base of karstification (Milanović 1992)

continuous underground flow, from Srđevići Ponor to the Trebišnjica springs, more than 34 km long. It is the base flow of this aquifer, to which the most important springs and infiltration zones belonging to Trebišnjica Springs are linked. These are huge springs, such as Vilina cave in Cerničko Polje and Obod with Baba Jama and Pribabići in Fatničko Polje. In a period of high water and maximum GWL, these springs function as an overflow for underground waters and, through them, the polje floods. At the same time, the main ponors are connected with basic flows: in Gatačko Polje a series of ponors—Srđevići, Jasikovac and Vranjača; then the Ključka River Ponor and other ponors in Cerničko Polje; and in Fatničko Polje, the Pasmica Ponor zone. In the dry period, between Gatačko Polje and the springs of Trebišnjica, only deep underground circulation exists. Then, only, the base flow is active, which is formed in the base of karstification and along the dominant transverse tectonic direction. In the wet period, there is very rapid saturation of the aquifer zone. This aquifer is characterized by relatively weak accumulation and retardation abilities but with exceptionally high transmissibility. But even high transmissibility

119

is still insufficient in comparison with the infiltration capacity of the area. Lack of retardation space underground is compensated for by accumulation of space of the closed areas of Gatačko, Cerničko and Fatničko Poljes. Higher levels of aquifers are characterized by weak retardation abilities, first, the part that discharges at the level of Fatničko Polje. Retardation capacity of this part of the aquifer is completely out of proportion to the water-conducting capacity of the same part of aquifer. Less than 12 h is needed for 90% discharge of the complete saturation of the highest part of the aquifer, at the level of Fatničko Polje. Numerous tracer tests have shown there is very fast circulation in this aquifer. The velocity of underground flows ranges from 0.9 to 14 cm/s, most often between 6 and 12 cm/s. In the dry period, between Srđevići and Trebišnjica springs, underground flow travels for 35 days. In a period of full aquifer saturation, underground flow passes this same distance in just 5 days. Fluctuations of aquifer level have all the characteristics of a well-developed karst. In the area of the tectonic knot maximum amplitude, 123 m were measured in PB-1 and 129 m were measured in F-3. The GWL changes in the period of rise and in the period of decline are very fast. The diagram of groundwater level fluctuations in PB-1 clearly indicates the presence of karst channels, with large water-conducting capacity, at an altitude of about 434 m, i.e., just above the base level of karstification. The function of the most significant concentrated zone of infiltration, Jasikovac/Vranjača and Pasmica, in a period of extreme precipitation can be completely blocked, temporarily functioning as springs. This is the period when the piezometric line in the background of these springs has the opposite slope from the general direction of circulation in this part of aquifer. There is a short period of time when the surface depression accepts all balance excess of the aquifer and it accumulates until the change of flow regime, that is, until the release of water flow capacity in that part of the aquifer, which represents a part of the drainage system of these poljes.

2.1.8

Catchment Areas Between Trebišnjica Spring Zones and Grančarevo

Downstream from the Trebišnjica spring zone to the Grančarevo (Lastva anticline) on both banks of the valley (the banks of the existing Bileća Reservoir), smaller separated aquifers were formed with the appropriate catchments. Downstream from Fatničko Polje, towards the southwest, the Trebišnjica spring catchment borders with the Bregava catchment in the west and with catchments of Ljubinjsko and Ljubomirsko poljes catchments, that is, with catchments of

120

2 Catchments, Surface Flows Springs

Fig. 2.10 Oko Spring, close upstream of the Grančarevo Dam sites, 1983 (Photo Milanović)

Bukov creek and Brova temporary river in the east. The water of these catchments discharges in the numerous springs along the right bank of the Trebišnjica valley, from the Čepelica Spring to Tučevac, downstream from Trebinje. Downstream from the Čepelica Spring zone, along the right side of the Bileća Reservoir, a few springs were registered: Lersko Oko (Eye), Hercegovačka Jama, Kopjela, Tmuša under Dubočani and Oko at the Grančarevo Dam site area, whose position is determined by position of dolomite barrier (Fig. 2.10). The catchment of the right bank can be divided into a part that gravitates towards the springs of Čepelica and towards two downstream sub-catchments. Based on hydrogeological characteristics and tracer tests of a couple of boreholes on the right side of the reservoir, it is possible to divide it into sub-catchments Orah and Mosko. By dye test of borehole B-4 (June 4, 1960), a connection was established with Hercegovačka Jama Spring in the reservoir space, and by dye test of M-4 (Skrobotno, 22.02.1965), a connection was established with Kopjela Spring, also in the reservoir space. The surface area of sub-catchments Orah and Mosko is 46 km2 and 34 km2, respectively.

Along the left bank of the reservoir, from the spring of Trebišnjica to the Lastva anticline, one spring is registered near the Dobićevo monastery and another in Montenegrin Miruše. At the level of the Trebišnjica riverbed, near the Dobrićevo monastery, there is the Oko Spring. It is a constant spring with large flow variations. During a period of precipitation, the flow reaches several cubic meters per second. The Kosijerevo-Dobrićevo and Crvene stijene stations spring is tapped for railway needs, with a gallery about 150 m long, connected to a 90-metre high well at the end of the gallery, in which the pumps are installed. This is currently used for the water supply of Petrovići, Vraćenovići and the surrounding villages in Montenegro. During heavy rainfall, part of the water from the Deleuša area flows into the reservoir as surface flow (torrent). Part of this water sinks and appears (probably) in Nikšić Spring. The northern and northwestern area of the catchment gravitates towards Dejan’s cave and to the Čepelica Springs. This has been determined with satisfactory accuracy. However, the eastern part of the catchment, towards the Zeta River basin, is very poorly explored. The boundaries of this part of the catchment have been determined aproximately. This part

2.1 Water Catchments and River Flows of East Herzegovina

gravitates toward the Nikšić Spring and springs along left bank of the Trebišnjica valley, with sub-catchments Deleuše (67 km2) and Petrovići (64 km2).

2.1.9

Sub-catchments and Springs Between Grančarevo and Gorica

These catchments (sub-catchments of the Trebišnjica regional catchment) are closed hydrogeological structures, in which the Trebišnjica riverbed represented the erosion base for the waters of the mountain massifs, both east and west of it. This sub-catchment is referred to as the Grančareno—Gorica intercatchment, although its downstream water divide is the Zupci fault. Along this section of the Trebišnjica catchment, flow does not sink. There are only springs; there are no ponors. Just downstream from the Zupci fault and upstream from the Gorica Dam, sinking zones, including estavelles, were formed. The Zupci fault zone with the Lastva anticline represents the regional hydrogeological boundary between the northern and southern parts of the regional Trebišnjica catchment. The Grančarevo—Gorica watershed includes three sub-catchments: Sušica and Oko on the left bank and Stara Mlinica (Old Mill) on the right bank. There are important hydrogeological/hydrological differences in their characteristics. Sub-catchment of Sušica and Zaslapnica Sušica has the only permanent surface flow and is the only tributary of the Trebišnjica River. The Sušica Spring, in the cave of the same name, is situated in the village of Vučja in Montenegro. In the dry season, there is no discharge. The cave was speleologically explored. The Sušica stream, with tributaries Zaslapnica (intermittent spring) and the Kunska River, originates in the dolomites of the Lastva anticline. Since most of the catchment is located in the Triassic dolomites, there is no sinking, so Sušica is a permanent flow formed primarily by a fluvial process. In the east, it borders the Grahovsko Polje catchment area (Grahovska River), with catchment of Risan Bay. The Grahovska River is a temporary torrential flow, whose maximum is estimated at 30 m3/s. This riverbed is actually a sinking zone along Grahovsko Polje. Underground, the waters that sink there flow towards Risan Bay. The connection with the Spila Spring in Boka Kotor Bay was determined by tracer test in Grahovsko Polje. Sušica merges with Trebišnjica downstream from the Grančarevo Dam, upstream from the Lastva settlement. It is a torrential flow with large flow variations, from approximately 0.2 m3/s to over 150 m3/s. The estimated catchment area is between 55 and 60 km2.

121

The Zaslapnica Spring (Montenegro) is located near the village of Zaslap, northwest of Grahovo, at an elevation of 770 m, on the fault between limestone and dolomite. According to the data of Gavrilović and Lj (1985), it is a constant spring of uniform discharge in the wet period of the year. There is intermittent discharge in the dry period. In the beginning, dry period discharge (July) varies in intervals. From about 5 h, there is between 200 and 160 l/s. The time between eruptions increases, from every 8 h, then every 12 h, to once every 24 h. In the driest part of year (August), according to measurements done by the same authors, discharge of Zaslapnica at the time of eruptions was about 180 l/ s. After 5 h, discharge decreases to 15 l/s. In their opinion, according to the duration of the eruption and the amount of discharged water, “that is the largest intermittent source not only in our country, than probably in the world”. Approximately 110 years ago, there were 15 operational cascading mills along the Zaslapnica River. In 1970, it was tapped for water supply for the village of Zaslap. Sub-catchment Oko (Gorica Area) Oko (Eye) Spring is a siphonic karst spring whose discharge varies between 0.5 and about 25 m3/s and, in extreme cases, probably more. Water flows out of the steep karst channel, several meters in diameter, which has been explored by drilling and diving to a depth of approximately 50 m. The channel ends at the previous water intake in the Trebišnjica riverbed (Figs. 4.111 and 4.112). Since the whole block of rock mass which forms the final part of the privileged zones of underground circulation is significantly tectonised and affected by karstification, aquifer deplantation occurs occasionally during high water levels through a number of smaller springs, approximately 100 m downstream from the main opening. It is important to note there are no permanent karst springs on the left bank of the Trebišnjica River, 4–5 km upstream and downstream from Oko Spring. The sub-catchment of the Oko Spring is, next to the Sušica sub-catchment, the most significant and richest in water section of the Trebišnjica. The catchment area of this spring captures water from the mountain area between Bijela Gora and Zupci. To the east and south, it borders with the catchment of Konavali, and probably the Boka Kotorska, and along the Zupci fault zone with the Trebinjsko and Mokro Polje catchments. These are terraines that are dominated by karstified limestones and dolomites of the Triassic, Jurassic, Cretaceous and Eocene periods. Although the sub-catchment of the Oko Spring borders the Sušica sub-catchment, their hydrogeological characteristics are elementally different. Sub-catchment Oko consists of exceptionally karstified Cretaceous limestones. In contrast to the dominant surface runoff in the Sušice sub-catchment, runoff in the Oko Spring sub-catchment is exclusively

122

2 Catchments, Surface Flows Springs

Fig. 2.11 Spring zone Šanik in the village of Donja Lastva (a) Active spring zone at the time of maximum reservoir level, 2010 (Photo Milanović), (b) Culvert beneath the road in Lastva for Šanik Spring water when the reservoir is empty, 2011 (Photo Putica)

underground. Because of the torrential character of runoff, it appears in the Sušica sub-catchment faster than in the case of the Oko Spring where, due to retardation, the runoff is slower. Excepting Oko Spring, the aquifer of this sub-catchment deplants on temporary spring Šanik, in Donja Lastva, at the level of the Trebišnjica riverbed (Fig. 2.11). Both springs are submerged by the Gorica Reservoir. The source of the Šanik works like overflow for the Oko Spring aquifer. When precipitation is more than 50 mm/24 h, the points of discharge are 5–7 m above the reservoir level. According to culvert dimensions, the maximum discharge of this zone can be estimated at more than 10 m3/s. The waters of the Orahovice area predominantly gravitate to this spring. The surface area of the Oko Spring sub-catchment is about 110 km2. The average annual precipitation exceeds 2500 mm. Daily precipitation of more than 100 mm is not uncommon in this area. The highest registered daily precipitation in the area, for the period 2010—in 2020, is 281 mm (Zupci, Bogojevića village, 29 October 2018). Sub-catchment of Stara Mlinica Spring This sub-catchment on the right bank of the Trebišnjica River is small. The only significant feature is the temporary spring Stara Mlinica, which is located under the Trebinje—Lastva road, above the maximum level of the Gorica Reservoir. Between Grančarevo and Lastva, several smaller springs are registered: Grmac, Nušila and Toplić. The drainage area of temporay springs on the right bank, from Grančarevo to Arslanagić bridge, is located in the hinterland of the right flank of the Bileća Reservoir and covers the area of Jasen and Budoši, with a surface area of about 45 km2. The largest amount of water of this sub-catchment discharges in the Stara Mlinica, in a locality known as Poklonac (Fig. 2.12). The upstream Mosko sub-catchment area of Stara Mlinica is separated by dolomites of the Lastva anticline. In the area of

Vrplje, toward Ljubomir Polje, there is a watershed between the sub-catchment of Stara Mlinica and the Brova catchment. The upstream part of the sub-catchment (Jasen) is in the Lower Jurassic dolomites. The Knez and Kneginja springs, which never dry up, create a torrent flow of a few cubic meters in seconds in a period of rainfall. In the Budoši area,

Fig. 2.12 Stara Mlinica (Old Mill), temporary spring in a rainy period, 2010 (Photo Milanović)

2.1 Water Catchments and River Flows of East Herzegovina

the flow enters in karstified Jurassic limestone. It sinks there and continues as underground flow towards the Stara Mlinica spring. Tracer that was injected into borehole B-2 in Jasen on 01.02.1956 appeared in Stara Mlinica (04.02.1956), as well as at a few smaller springs between Stara Mlinica and the Grančarevo dam site. Results of tracer tests of boreholes M-4, B-4 and B-6, northeast (upstream) from the axis of the Lastva anticline, and of B-2, southeast of the core of the Lastva anticline, make possible the delimitation of the Mosko sub-catchment, with the downstream Stara Mlinica sub-catchment (Jasen/ Budoši area). In the case of Stara Mlinica, the process of karstification took place much more slowly, with regard to fluvial erosion and cutting of the Trebišnjica riverbed, so that the spring is located around 30 m above the level of the riverbed. Water discharges out from the karst channel which is, during the dry period, accessible for speleological research. About 90 m of

123

the channel was investigated, of which more than half was submerged (Milanović & Vasić, 2022).

2.1.10 Catchment Areas of Trebinjsko, Popovo and Mokro Polje The catchments of Trebinjsko, Popovo and Mokro Poljes represent a unique hydrogeological unit, south of the Lastva anticline. The catchment of Trebinjsko Polje includes the sub-catchment of Ljubomirsko Polje i.e. the Brova stream catchment. The Popovo Polje catchment include the Ljubinjsko Polje sub-catchment, that is, Bukov creek catchment. The border determination of these catchments is exceptionally complicated because they have characteristic of bifurcation zones. Figure 2.13 presents the watersheds of these three poljes.

Fig. 2.13 Catchments of Popovo, Trebinje and Mokro poljes, 1. Permanent spring, 2. Temporary spring, 3. Ponor, 4. Estavelle, 5. Established underground connection, 6. Watersheds (Milanović, 2021)

124

2 Catchments, Surface Flows Springs

Fig. 2.14 Hydrogeologic/hydrologic model Trebinjsko-Mokro-Popovo Poljes. A. Bottleneck area choking the flow from upstream (Milanović, 2021)

The exact mutual demarcation of these three catchment areas is practically impossible, and it is presented here approximately. The hydrogeological/hydrological model of these poljes (Fig. 2.14) is significantly different from the hydrogeological/hydrological model Trebišnjica—Bregava, which is presented in Chap. 1 (Fig. 1.28). While the Trebišnjica—Bregava model is characterized with almost exclusively underground flows, surface flow of the Trebišnjica River dominates in this model. All poljes are connected, including surface inflow of part of the water through the Gorica dam site. Another significant difference is that the water from this system flows exclusively underground toward the seacoast and the Neretva valley, and it discharges through numerous springs and submarine springs over a long stretch, across 150 km, from Robinson Springs on the seacoast to Hutovo Blato in the Neretva valley. An important component of this model is the specific runoff regime that is a consequence of the disproportion between the large and intensive inflow into the karst area and the drainage capacity of the karst system, which is especially pronounced near Mokro Polje. Inflow in the polje and outflow from the polje occures through the estavelles at the polje bottom. Because there is insufficient capacity of the drainage system of the karst channels to accept all daily precipitation, which is often 100–200 mm, drainage channels

become clogged (choked), the water level in to them grows to the level of the polje, water discharges out of the polje through the estavelles, and the polje floods. The polje demonstrates natural retention, which temporarily stores a part of the water which, due to bottleneck choking of karst channels, discharges out in the polje (Fig. 2.15). In natural conditions, Mokro Polje, which morphologically and genetically forms a whole with Trebinjsko Polje, has certain hydrogeological/hydrological specificities. Water of this polje does not gravitate to the Trebišnjica River, or that connection is realized only in a period of heavy rainfall and flooding in the polje. Tracer tests of Trap and Trnje estavelles confirmed the underground connections between Mokro Polje and Duboka ljuta (Robinson) Spring, and Zavrelje Spring on the seacoast. By tracer test, the connection between the cavern in the tunnel Gorica—Plat (0 + 216) and tail race tunnel II in Plat was established. The connection is also confirmed with the appearance of cloudy water at the source of Zavrelje, after collapse in the main drainage canal in Mokro Polje. The drainage area of Mokro Polje consists of: the sub-catchment of Petrovo Polje with the watershed towards Trebinjsko Polje; the sub-catchment of the Abatno Polje and sub-catchment of the Luke area with a watershed towards the sea coast; and the sub-catchment of the Mokro Polje area between Zgonjevo and Bugovina, which covers the Zupci

2.1 Water Catchments and River Flows of East Herzegovina

125

Fig. 2.15 Mokro Polje. Flood model. (a) Free surface flow beneath the polje, (b) After rain, the system comes under pressure and groundwater level rises, (c) Due to heavy rain, the downstream karst channels create a bottleneck, choking the flow from the upstream area Q3. Water level rises in the upstream channel. Estavelles become springs and flooding begins, (d) Rain stops, pressure decreases and estavelles become ponors (Milanović, 2021)

region up to the Zupci fault. The total surface area of Mokro Polje catchment is about 90 km2. The greater part of the northern border of the Popovo and Trebinjsko poljes catchment are the Brova catchments in Ljubomir and the Bukovo creek in Ljubinjsko Polje. The specificity of these poljes is that they have their own catchments and they are outside the system in which waters overflowing from higher to lower cascades means karst poljes. In the genesis of both poljes, the folded structure with dolomites in the core plays a key role. The catchment area of Ljubinjsko Polje is especially hydrogeologically isolated and represents some type of hydrogeological enclave. By tracer test of the Ždrijelovići ponor zone in Ljubomir Polje, and underground connection is established, with 14 springs along the right bank of Trebišnjica, from the Arslanagić bridge to Dražin do (Tučevac temporary spring). The small catchment area of Zmijanac Spring belongs to the Ljubomir sub-catchment. The catchment of Ljubinjsko Polje (Bukov creek) to Popovo Polje is defined by the data of tracer tests of the Konac Polje (1960) ponor and is based on only one questionable sample with dye (?) in the water sample from the Meginja estavelle in Strujući. According to this datum for the western border of the catchment (toward Hutovo Blato and Bregava springs), the approximate direction of Žegulja— Čavaš was adopted. According to this concept, the Ljubinjsko Polje sub-catchment belongs exclusively to the Popovo Polje catchment, with a possible connection under the polje towards the seacoast. There is a real possibility that sinking water at the very western end of the polje flows towards Hutovo Blato and perhaps toward the Bregava valley. This means that this part of the polje has characteristic

bifurcation zones. The hydrogeology of Ljubinjsko Polje needs to be checked. The south border of the Trebinjsko and Popovo Polje catchments can be considered their own southern rim, along which there is a series of ponors and estavelles, with a huge capacity of discharge. From Trebinje to Zavala in Popovo Polje, the southern border of the Trebišnjica riverbed catchment can also be accepted, since a large number of ponors and estavelles are located along it. All precipitation south of this part of the Trebišnjica flow, until the village of Strujići, sinks and flows towards the seacoast, primarily towards Ombla spring. In the dry season, except for inflow as surface flow through the Gorica Dam siteand around it as undeground flow, there are no other inflows into these poljes. It is also important that part of the water that sinks in the area of these catchments never appears on the surface, because it flows exclusively as underground flow towards the springs on the seacoast. Based on the lithological and hydrogeological characteristics of the Zavala—Ravno—Strujići area, it is possible to estimate the position of the border area between upstream and downstream of Popovo Polje. In the Zavala— Ravno section, the smallest losses were measured during simultaneous measurements along the Trebišnjica riverbed, in natural conditions. In some measurements, there are registered inflows while, in all other sections, large losses (sinks) are simultaneously measured. The Čavaš—Turkovići line was adopted as the watershed in Popovo Polje because, in this area, the last estavelles were registered. Further, toward the downstream part of the polje, there are ponors exclusively. This is where the bifurcation zone begins, with ponors of large swallowing capacity. The position of watershed of the catchment area south of Ravno and Zavala,

126

depends on position of springs along the southern edge of the polje—Pokrivenik, Lukavac (below Vjetrenica) and Čvaušnik. It is obvious that part of the water from the hinterland of Ravno and Zavala flows toward Popovo Polje. Due to this fact, the watershed of the catchment area is south of the edge of the polje. The total catchment area of Popovo and Trebinjsko Poljes is estimated at 775 km2, of which 94 km2 is Ljubinsko Polje sub-catchment and 119 km2 is the Ljubomirsko Polje. The size of the Ljubinjsko Polje sub-basin is valid, if the assumption that all water flows toward Popovo Polje is correct. If it is a bifurcation zone in the lowest part of the polje, then the surface of this sub-catchment is about 65 km2. The complexity of the Trebinjsko, Mokro and Popovo Polje catchment areas, makes a more complex relationship between the catchments and the absolute erosion base level, the sea basin. Among them, the Omble catchment dominates, which includes a large part of the three analyzed catchments. Watersheds between these catchments are susceptible to permanent changes in space and time, especially in a period of high precipitation, when they are then subject to daily changes. It is one big bifurcation area. On the basis of geological mapping, numerous tracer tests, investigation drilling and geophysical research, there are catchment affiliations of individual coastal springs: – Mokro Polje (Zgonjevo—Luke) belongs to the catchment of Robinson (Duboka ljuta). After construction of the siphonal culvert under the pipeline in Mokro Polje, including the dewatering canal, it belongs partially to the Popovo Polje catchment. – Trebinjsko Polje is in the catchments of Popovo Polje, Ombla Spring and Zavrelje Spring. – Trebinjska Šuma, Lug and Popovo Polje, up to Sedlari, are in the Ombla catchment but, simultaneously, in the downstream part of the Popovo Polje catchment area. – The Popovo Polje between Sedlari and Ravno partially belongs to the spring zone in Slano area at seacoast, however the belonging of larger part of this area is unknown. – Popovo Polje, between Velja Međa and Turkovići, along with Mlinica (Bandera), Provalija and Doljašnica ponors (distinct bifurcation zone) belongs to the Budaima— Bistrina catchment on the seacoast and the Hutovo Blato cryptodepression. – The lowest part of Popovo Polje, along with the ponors Crnulja, Ponikva, Žira, Lisac and Kaluđerov, belongs to the catchment of the spring zones in the area of Svitava and the Neretva valley, near Metković.

2 Catchments, Surface Flows Springs

2.1.11 Characteristics of Trebišnjica River Through the Popovo Polje In natural conditions in the Trebišnjica River out of a total of 90 km of flow, about 62 km was temporary flow that was active only in the wet period of the year. However, it is the most important river of East Herzegovina, and it is known as the largest European sinking river. The flow of Trebišnjica originates from large karst springs—Dejan’s cave, Nikšić Spring and Čepelica Springs—whose characteristics are shown in Sect. 2.1.5. From the spring zone (Bileća Springs) to the Oko Spring, along the flow of the Trebišnjica, there are no losses. Downstream from the Grančarevo Dam, the Trebišnjica riverbed cuts into impervious Triassic dolomites in the core of the Lastva anticline. The first place there is water loss is the Gorica estavelle, approximately 540 m upstream of the Gorica dam site. This estavelle mostly serves as a ponor. Through it, the water drains away from the Gorica Reservoir, toward the Lušac Spring and the Oko Rasovac karst shaft, and one part is probably directed toward the Ombla Spring. After construction of the Gorica Dam, this estavelle was submerged by the reservoir and temporary spring Lušac in Upper Police urban area and became permanent. Under natural conditions, during the dry period, Trebišnjica flow dries up downstream from Trebinje, near Dražin do. Then, about 3 m3/s flows through the urban area of Trebinje. From Trebinje to Dražin do, part of the flow separates from the main riverbed and forms the Pridvorci river-branch that rejoins the main stream downstream. Along this branch, several ponors and estavelle zones are registered. In the main riverbed, there are also ponors registered (Fetahagića shafts, etc.). Below Mostaći, before Dražin do, there are a couple of large temporary karst springs (Tučevac, Oko in Zasad). Downstream from Dražin do, along the northern edge of the karst plain the Trebinje Forest, the Trebišnjica River cuts a shallow canyon, 13 km long. It is a temporary part of the Trebišnjica River flow, which extends for another 50 km approximately, to the Ponikva Ponor at very end of Popovo Polje. This ponor is the last point of Trebišnjica surface flow. In the wet period, when the underground rock mass is saturated, the Trebišnjica River flows the whole length from Dražin do to the Ponikva Ponor. Then, flow increases up to hundreds of cubic meters per second, even more at the maximum. At the water gauging station in Dobromani, on several occasions there has been flow of more than 1000 m3/ s. For example, on 02.12.1903, the measured flow was 1362 m3/s, on 24.03.1915, it was 1307 m3/s, and on

2.1 Water Catchments and River Flows of East Herzegovina

127

Fig. 2.16 Hydrological/hydrogeological gauging station for monitoring groundwater level beneath the Trebišnjica riverbed and simultaneous hydrological measurements of river flow 1970 (Photo Milanović)

01.03.1945, measured flow was 1065 m3/s. Trebišnjica reaches its highest flow downstream from Ravno after receiving the huge amount of water that discharges along the Dračevo—Strujići estavelle zone. There, the flow can be greater than 1400 m3/s, which far exceeds the sinking capacity of all the ponors, so the polje floods. Sixteen piezometer cross sections were drilled, perpendicular to the river bed, in order to register sections along the riverbed with high uplift of underground water, as well as sections where the groundwater level never reaches the riverbed level. These profiles are located in thearea of Mostaći, Tvrdoš, G. Kočela, D. Kočela, Lug, Dobromani, Žakova, Tulja, downstream from Poljica, downstream from Grmljan, downstream from Zavala (right branch), downstream from the of the bridge the in Ravno, downstream from the Strujići, Čavaš, between Dvrsnica and Velja Međa, Turković near the Provalija Ponor and near Dobri do. Each profile consisted of three boreholes on both banks, separated from each other by 30 m. The depth of the boreholes was from the 20 to 40 m.

Due to simultaneous measurements of water losses along the riverbed, some of these profiles are equipped with hydrological gauge stations. An additional piezometric borehole was drilled in the middle of the riverbed. One characteristic hydrological/hydrogeological profile (near Kočela) is shown in Fig. 2.16, and the measurement of groundwater level oscillations from the same profile in is shown in Fig. 2.17. Figure 2.17 shows water levels in the piezometric boreholes during the period when it flows through the riverbed, a few tenths of cubic meters of water. Through simultaneous measurements in a wet period (high levels of underground water), it was determined that losses along the riverbed are 24.4 m3/s. These losses were noted in the section between Gorica—Provalija, on a length of approximately 60 km of flow (Fig. 2.18). The last section, from Provalija to Ponikva Ponor, was under flood water. In the dry period, an experiment was carried out to determine the losses along the riverbed, in conditions when the underground is capable of maximum water intake (low levels

128

2 Catchments, Surface Flows Springs

Fig. 2.17 The relationship of river water level and piezometric levels in a hydrogeological crosssection of the Trebišnjica River near the village of Kočela (Milanović, 1981)

of underground water). From the Gorica Reservoir, water is constantly released at 50 m3/s. It was confirmed that cumulative seepage along the Trebišnjica riverbed is 39.4 m3/s. At the end point of the surface flow of Trebišnjica River, at the Ponikva Ponor, it reached only a few hundred liters of water per second. When it is under the same conditions (during a dry period), from the 150 m3/s released by the reservoir into the riverbed are measured maximum losses of 63.4 m3/s (Šimunić & Žibret, 1970). During this flow, large ponors are also activated at the level of the riverbed (Doljašnica, Provalija, Crnulja, Lisac). Including these losses, the total sink capacity in the Trebišnjic riverbed exceeds 130 m3/s. The other ponors are located outside the riverbed and receive water only when the polje floods. In the summer period, part of the Trebišnjica riverbed in the Kočela area is dry. The groundwater level is then at a greater depth than the bottom of all boreholes (Fig. 2.17). In the period of rainfall, water flows through this part of the riverbed, and the underground water level rises significantly but never reaches the riverbed level. While 10–30 m3/s flows through the bed for months, the underground water level is 23 m (or lower) below the bottom of the riverbed. This profile is characterized by large water level differences between individual piezometric boreholes. Although they are located at small mutual distances and in a lithologically homogeneous environment, the difference between levels in the neighboring piezometers can be up to 17 m. This level difference is a consequence of the ratio of absorption capacity of the ponor zone along the riverbed and permeability of the karst system (karst channel) in rock mass under the riverbed. Due to the drainage capacity

at this locality is much higher than absorption capacity of ponor zone groundwater level can’t arise. The data of the 16 profiles mentioned were analyzed. It was established that there are different relationships between surface and underground water along and below the Trebišnjica riverbed. By generalizing these relations, four basic cases were distinguished, which are shown schematically in Fig. 2.19. In the first case (A), when the riverbed is dry, GWL is deep under the riverbed, sloping toward the south, that is, toward the sea. In a wet period, when water flow is active, the piezometric line touches the riverbed (right bank of Trebišnjica) and feeds it by surface flow but, at the same time, part of the water sinks through the ponors along the left bank. In the second case (B), the minimum GWL is below the riverbed and is inclined to the north, that is, opposite to the direction of the erosion base. This is explained by the influence of relative underground karst drains of high permeability which, in a period of minimum levels, performs the role of local erosion base levels. At maximum levels, these drains are submerged and thereby lose the function of the base levels. In that period, the GWL rises to the level of the riverbed, and the slope of the piezometric line is toward the south. In the third case (C), even at the highest flows in the wet period of the year, the GWL never reaches the level of the Trebišnjica riverbed. These are parts of Trebišnjica flows with permanent sinking. The fourth case (D) is similar to the previous one, except that the piezometer line is uneven. This is a consequence of

2.1 Water Catchments and River Flows of East Herzegovina

129

Fig. 2.18 Graphical presentation of the total (cumulative) water swallowing capacity of ponors along the Trebišnjica riverbed 1981 (courtesy Energoinvest, Sarajevo)

the presence of channels with high permeability under the riverbed, i.e., positively indicates the existence of a zone of intensive karstification with the role of local erosion base level.

2.1.12 Zalomka River Catchment Area Catchment areas of Zalomka River, the northwestern part of the Nevesinjsko Polje and the immediate catchment of Buna River form a unique entity. The waters of these catchments

form a karst aquifer that it empties through two large karst springs (Buna and Bunica) that are not physicaly (hydrogeologically or hydraulically) connected. Under term catchment of Zalomka implies area from its spring zone close to Gatačko Polje until the end of its flow in the Biograd Ponor. Catchment area includes the valley of Zalomka, the southern part of Nevesinjsko Polje and the catchments of Drežanjka and Zovidolka rivers. All of the above flows are active in wet period year, only. The Zalomka catchment area is bordered on the east and south by the Trebišnjica catchment area, on the north by the

130

2 Catchments, Surface Flows Springs

Fig. 2.19 Various relationships of river water level and groundwater level along the Trebišnjica River (Milanović, 1979)

Neretva catchment area, and towards the west by the intercatchment (immediate catchment) of the Buna and Bunica, that is, the lower section of the Neretva River. Towards the south, it also borders on the catchment of Dabarsko Polje (Fig. 2.20). The area towards the north, between the Zalomka valley and the upper course of the Neretva River, is built of sediments of Cretaceous flysch and, partially, Triassic dolomite (eastern rim of Nevesinjsko Polje). These geological formations are the subject of fluvial erosion, not karstification, so the net flow in them is superficial. This is why the watershed of these catchments is orographic. Part of the watershed towards the east (Gatačko Polje) is characterized by a bifurcation zone in the karstified limestones near Rašćelica. It is a small ridge which orographicaly shares Gatačko Polje from the Zalomka valley. The position of the underground hydrogeological water divide depends on the current saturation of the local aquifer, i.e., it depends on the underground water level. When the groundwater level is high, water discharges at the surface and creates the Đeropa creek, which flows toward the west (toward Zalomka) and belongs to the catchment area of Nevesinjsko Polje. In the case of low GWL, level water sinks in the same zone, and both surface and underground flows flow in the opposite direction—to the east (toward Gatačko Polje, Jezerine) and belong to the Trebišnjica catchment. The Jugovići creek, after merging with Đeropa creek, creates the Zalomka River. From the Rašćelica area to the south, the border of the catchment area follows a part of the Lukovica reverse fault, Gradina—Zalom. A hydrogeological barrier that stretches along this fault prevents underground flows to the south. Along this contact, there is a series of ponors in which water sinks and flows towards the Obod

Spring in Fatničko Polje. This has been proven by tracing underground flows in the ponors near Lukovica and Gradina. Water north of the mentioned reverse structure remains in the Zalomka catchment. There is no valid data for the wider area of Šipačno, so the watershed between the Slato Polje (catchment area of Nevesinjsko Polje) and the Trebišnjica catchment is approximate. For a more precise definition of these borders, additional investigations of the Šipačno area are necessary. The western border of the Zalomka catchment is towards the Trebišnjica catchment. The southern border toward to the Dabarsko Polje catchment, including the Drežanjka and Zovidolka catchments, borders with the catchment of Lukavačko and Trusinsko poljes. At many places in the mountain massif of Trusina, the catchment borders of Nevesinjsko Polje are approximate. The surface area of the Zalomka catchment to the water gauging station (WGS) Pošćenje is estimated at 512 km2.

2.1.13 Catchment Area of Northern Part of Nevesinjsko Polje This catchment area consists of several sub-catchments of torrential flows that sink into several larger and a number of smaller ponors. By swallowing capacity, the following are important: Ždrijelo, Zlatac and Babova Jama. Of about 15 torrential flows, Alagovac and Dušila creeks are more significant (Fig. 1.95). The approximate border between the Zalomka catchment in Nevesinjsko Polje and the catchment in the northwestern area is also a wider area—Nevesinjsko Polje to the village of Kifino Selo. All waters of this area discharge exclusively at Buna Spring. The estimated surface of this catchment area is about 320 km2.

2.1 Water Catchments and River Flows of East Herzegovina

131

Fig. 2.20 Catchment areas of Buna and Bunica Springs. 1. Karst spring, 2. Ponor, 3. Watershed (Milanović, 2021)

2.1.14 Catchment Area Between Nevesinjsko Polje and Buna-Bunica Springs This part of the catchment (so called inter-catchment) captures mountain massife of Veleža, with the highest top at 1967 m a.s.l. and the spacious plateau of Podveležje subdivisions, as well as part of the Trusina and Snježnica mountains. Between the Buna Spring catchment and the springs in Bijelo Polje, upstream of Mostar, the water divide is established (by tracer tests of the ponors) in the Velež area (Hansko Polje). At the same time, it is a bifurcation zone. The other parts of the watersheds are determined approximately on the basis of hydrogeological and geomorphological characteristics of terrain. The Buna and Bunica springs are at a mutual distance of about 4 km but, physically, a relationship between them does not exist. The springs are separated by a hydrogeological barrier formed by reverse fault, along which the karstified limestones are overthrusted over zones of sandstone, marl, conglomerate and limestone of the Paleocene age. Both springs are formed in the contact limestone with Miocene sediments (marls, clay, conglomerates) that are deposited in Mostar Polje. Determining the catchments that belong to the area west of Biograd Ponor is a particularly complicated task. This is an area with relics of a fluvial network of the former Zalomk River, from the Biograd Ponor to the Bregava River, downstream from Stolac. Part of this network creates the upper flow (dry valley Radimlja) and the valley of Zmijski creek (snake creek), Fig. 2.21. Disorganization of the fluvial river network that preceded the process of karstification and formation of the Biograd

Ponor is described in detail in Sect. 2.1.20—Evolution of the karst aquifer in the Bregava catchment. The mentioned area is lithologically and tectonically very complex. The surface terrain is built of hydrogeologically different rocks, fromkarstified limestone to flysch and conglomerates of the Promina formation. It is crossed by the regional reverse fault. The Biograd Ponor and the Radimlje valley are connected by a dry valley, with a ridge around an altitude of ~830 m. All waters of the Zmijski potok (Snake creek) and the Radimlje valley that belong to the surface catchment area flow towards the Bregava, and the waters that sink in that area (at least 30 km2) flow as underground flows towards Bunica Spring. The waters that sink into the Biograd and Krupac Ponor flow under the mentioned catchment of Zmijski potok toward Bunica Spring. The Biograd Ponor is located north of the mentioned reverse fault. Its link with Bunica is most likely achieved through the zone where this fault is disconnected by tectonic movement and has locally lost its function as barrier. Generally, however, the border of this catchment can be identified towards to the south. This part of the catchment area of Buna and Bunica is estimated at about 300 km2.

2.1.15 Characteristics of Zalomka River In period that preceded intensive karstification, the Zalomka valley was one of the outflows of Gatačko Polje. Along the flow, Zalomka is divided into three sections with different names. The most upstream and temporary part of the flow,

132

2 Catchments, Surface Flows Springs

Fig. 2.21 Nevesinjsko Polje. Area between the southern part of Nevesinjsko Polje and Buna and Bunica springs, including the Radimlja valley (Milanović, 2021)

from Rašćelica to Fojnice, is named Đeropa. The longest part of the flow, from the village of Fojnica to the confluence of the Zovidolka River is named the Zalomka River. The most downstream part, up to the Biograd Ponor, is named the Kolješka River. For the last fifty years, the entire course, from Rašćelica to the Biograd Ponor, has been named Zalomka. Between Gatačko and Nevesinjsko Poljes, the Zalomka valley is cut into carbonate sediments that consist of Upper Triassic, thick-bedded to the massive dolomites, and Jurassic limestone with dolomites and chert. Between Gradina and the area of Crni Kuk, the Zalomka riverbed is cut in dolomites in the northeastern wing of the Zalomka anticline. As in the case of the Lastva anticline, these dolomites are also subject to grussification and erosion, so that part of the Zalomka valley is distinguished by morphological forms of less contrast. At the same time, this is the only part of the Zalomka riverbed where the water does not sink. Downstream from Crni Kuk to the entrance to the Nevesinjsko Polje, the riverbed is in very karstified limestone, with numerous ponors and estavelles. Entering Nevesinjsko Polje, the Zalomka riverbed passes through the sediments of the Neogene until upstream from

Budisavlje, where it enters into Cretaceous limestone. Downstream, part of the riverbed from the Ždrebanik estavelle to the Biograd Ponor is cut into a conglomerate of the Promina formation. The flow of the Zalomka River and its tributaries was measured at a large number of hydrological water gauge stations, the most significant of which are Rilja, Kifino Selo, Šnjetica and Pošćenje (Fig. 2.22). Next is a brief presentation of the results of processing data for WGS Rilja and WGS Pošćenje for the period from 1966 to 1985. The Zalomka flow at WGS Rilja is active, on average, for 213 days annually, with the most frequent flow from 0.5 to 2.0 m3/s. In the remaining period, the flow dries up. The maximum flow measured was on 13.10.1975, Q = 122 m3/s. On average, the flow is Qav = 4.61 m3/s. At the WGS Pošćenje (close to Biograd Ponor), Zalomka flow is active about 212 days annually, other days the riverbed is dry. The most common flows are between 1.0 and 8.0 m3/s. The maximum flow was registered on November 18, 1968, Q = 440 m3/s. Average annual flow is Q = 11.2 m3/s.

2.1 Water Catchments and River Flows of East Herzegovina

133

Fig. 2.22 Zalomka River, longitudinal profile with position of hydrological gauging stations. Courtesy Energoinvest, Sarajevo

2.1.16 Investigations Along the Zalomka River Along the flow of the Zalomka River, four potential dam sites were investigated in detail: Nadanići, Rilja, Šnjetica and Pošćenje. Dam site Nadanići, in the area of Rašćelica was investigated, for a dam height of 20 m with elevation of the crest at 973 m. Seven investigation boreholes were drilled (Fig. 2.23). Geoelectrictrical investigations and adit excavation investigations were organized. Although Rašcelica is a surface watershed between Gatačko Polje and the Zalomka valley, it is not a water divide for groundwater. A strong underground link with Jezerine Spring, close to Nadanići, was established by tracer injection into the ponor, next to Rašćelica, towards Fojnica (LJ. Jadrijevic, S. Krga). Between Rašćelica and Fojnica, the Zalomka valley stretches towards Gradina, which is formed along the reverse fault of Triassic dolomites and Eocene flysch. This contact extends from the Gatačko Polje across Lukovica and Gradine toward Ljeskov Dub, and further to Bratač and Nevesinjsko Polje. Along discordant contact between Eocene flysch and Cretaceous limestone (south rim Lukovica and Gradine), there are a couple of ponors. Hydrogeologically, the Gradine catchment belongs to the Trebišnjica catchment area, established by tracer test. During extreme rainfall, the sinking capacity of these ponors in Lukovice is not sufficient, and that area floods. Between Gradina and Zalom, the massive and thickbedded Triassic dolomites form an overthrusted wing of the recumbent fold which, together with the Eocene flysch, plays

a hydrogeological role of barriers toward the lower erosion base in a southern direction. In this way, a closed hydrogeological structure is created, with only one possible direction of flow for underground and surface waters along the valley of Zalomka. Downstream from the village of Fojnica, after inflow from the Jugovića creek, a short permanent Zalomka flow is formed. From there to Crni Kuk, the Zalomka flows over Triassic dolomites (Fig. 2.24). Although in summer it is a very small flow, this is the only permanent flow of Zalomka. At the Crni Kuk area flow sinks; like that in the dry season, the riverbed to the Biograd Ponor is dry (Fig. 2.25). Since it is a planned storage space in rock masses that are affected by the process of karstification, the question of its water permeability is crucial. To obtain a reliable answer to this question, numerous investigation works were done along the Zalomka River. Special attention was focused on the part of the Zalomka valley between Crni Kuk and Rilja. Along with detailed geological mapping, the following exploration works were also carried out: seven exploration boreholes were drilled along the riverbed up to 40 m deep (from K-1 to K7); nine boreholes were drilled on the Rilja dam site, four on the left bank, two on the right bank, and three at the bottom of the valley (from RB-1 to RB-11). Geophysical logging was carried out in them. Downstream from Crni Kuk (2 km), two geophysical (geoelectric) lines were run. Part of the underground flow of Crni Kuk downstream was followed by tracer works in 1972/73 and in 1986. Exploratory drilling of all boreholes in the Zalomka valley, and excavation of walled-in ponors with steel cavers, in order to be ready for tracer tests with Na-fluorescein, were

134

2 Catchments, Surface Flows Springs

Fig. 2.23 Zalomka River, dam site Nadanići. 1. Conglomerates, 2. Flysch, 3. Limestone, 4. Dolomites, 5. Large temporary spring, 6. Small temporary spring, 7. Small permanent spring, 8. Borehole, 9. Large ponor, 10. Ponor, 11. Group of closely spaced ponors (Milanović, 2006)

carried out by the Development Service of Hydropower System Trebišnjica. In December 1972, 50 kg of Na-fluorescein was injected into the K-1 borehole. A labeled wave appeared in the bed the next day 80–100 m downstream and flowed to the Rilja ponor zone. After sinking in this zone, the dye appeared in the Ovčiji Brod Spring after 6 days, in the Buna Spring after 17 days, and in the Bogodol creek after 27 days (one sample?). The connection with Buna was achieved after the surface flow re-sunk in the bed of Zalomka near Budisavlja (Ždrebanik zone). This time, the Zalomka flowed to Marića Vir. From Marića Vir to Oko Spring near Šnjetica, the riverbed was dry. For tracer tests of borehole K-3 (01.02.1973), 17 kg of dye was used. A labeled wave appeared in the riverbed downstream from WGS Rilja and flowed through the bed to the Rilja ponor zone, and again appeared at the Ovčiji Brod (05.02.1973), Pojila Spring close to Bogodol creek (10.02.1973), and in the Zalomka riverbed, downstream of boreholes B-1 and B-3. At the time of dye injection, the

following water levels were registered: WGS Rilja 21 cm; WGS Šnjetica 13 cm; and WGS Kifino selo 32 cm. From Rilja to the K-6, the riverbed was dry. Radioactive isotopes with a short half-life decay were used to investigate this ponor zone. This tracer was injected into the flow upstream of the ponor zone. Shortly after the injection, the flow became completely frozen, so the larger part of the isotope remained trapped in the ice. The dye-tracing of the ponors near Crni Kuk was repeated on 05.07.1986, with 30 kg of dye. With this tracer test, it was established that the underground flow follows the Zalomka River at a relatively shallow depth below the riverbed (“river below river”). The presence of dye was registered at the Babića Spring (visually, by eye) in boreholes K-3, K-5, RB-1, RB-5, RB-9 (low concentration), RA-1 (low concentration) and RA-3. Downstream from Crni Kuk, a part of the water sinks in alluvial deposits, flows very shallowly, and discharges at more places on the surface than the definitive sinking has occurred in the Rilja ponor zone. That water discharges in the

2.1 Water Catchments and River Flows of East Herzegovina

Fig. 2.24 Zalomka riverbed situated at grussified Triassic dolomite, 1973 (Photo Milanović)

135

spring on the rim of Nevesinjsko Polje, near Ovčiji Brod. Underground connections of waters that sink into the riverbed of Zalomka from the Rilja dam site to Ovčiji Brod and Ždrebanik are shown in Fig. 2.26. In the left bank, between the Rilja dam site and Triassic dolomite, six investigation boreholes (from RA-1 to RA-6) were drilled. Eleven boreholes were drilled along the route of the tunnel from Rilje to Budisavlja (from NT-1 to NT-11, Fig. 2.27). At the dam site, the exploratory adit was excavated. Boreholes K-1 and K-3 were used for tracer testing, as well as the Babića estavelle, Brljuške and the Moraj Luke ponors. Investigations confirmed that future Zalomka Reservoir space, from Fojnice to the Rilja dam site is situated in a closed hydrogeological structure without observed indications, which puts its waterproofing under question. Some of the ponors in the Zalomka alluvium have been excavated down to the bedrock (Fig. 2.28). In one of them (upstream from Rilja), a karst channel was discovered under the riverbed, about 1.8 m high. The channel was only accessible for a few meters. A couple of ponors (downstream from Rilja) are walled in and covered with lids, to be easily accessible for tracer tests. It was also observed that, during high precipitation, water under pressure breaks out from borehole K-4 (fountain jet 0.5–0.7 m). All tracer tests in the Rilja ponor zone showed a link to the springs near Ovčiji Brod, and a tracer test of the Moraj Luke

Fig. 2.25 Zalomka River downstream from Kifino village (riverbed—dry and with flow, 1971/72 (Photos Milanović)

136

2 Catchments, Surface Flows Springs

Fig. 2.26 Established underground connections in the area of the Zalomka River and Nevesinjsko Polje. 1. Boreholes, 2. Closely spaced boreholes at dam site, 3. Ponor or ponor zones, 4. Established underground connection, 5. Temporary spring (Milanović, 2006)

Fig. 2.27 Position of boreholes in the area of Rilja—Budisavlje. 1. Limestone, 2. Rocks with rolls of relative and absolute hydrogeological barrier, 3. Dolomites, 4. Permanent small spring, 5. Large temporary spring, 6. Ponor, 7. Borehole (Milanović, 2006)

Ponor showed a link to the Zalomka River near Rilja and Ovčiji Brod. With these investigation works, it was established that the Jurassic limestones that build the left slope of the Zalomka valley are intensively karstified. It is a zone between Triassic dolomites of Crni Kuk and Cretaceous

limestone, with interlayers of marl and sandstone in the Bratač area (Fig. 2.29). Both of these masses are less susceptible to karstification compared to Jurassic limestones. Between them, in the Jurassic limestones, a zone of concentrated infiltration was

2.1 Water Catchments and River Flows of East Herzegovina

137

Fig. 2.28 Zalomka River, Rilja. (a) Excavation of river alluvium to the ponor in limestone river bottom, (b) Hydrologic structure for measurement of ponor sinking capacity, 1971 (Photos Milanović)

Fig. 2.29 Schematic presentation of the hydrogeological corridor between the Zalomka River in the Rilja section and the Zalomka River between Ovčiji brod and Budisavlje. 1. Triassic dolomites, 2. Cretaceous limestone with marly and sandstone layers and Eocene flysch, 3. Zone of karstified Jurassic limestone with concentrated underground flow, 4. Direction of underground flow, 5. Base flow zones, 6. Permanent surface flow, 7. Temporary surface flow, 8. Piezometric lines (Milanović, 2006)

138

formed, that is, the hydrogeological corridor through which sinking waters flow. A zone of Eocene flysch, along with the reverse fault of Zalom village, is not deep enough nor thick enough to prevent development of karstification toward thedownstream part of the Zalomka River. Figure 2.29 (A, B and C) shows three possible hydrological/hydrogeological conditions in the Rilja ponor zone. In the dry period (A), the surface stream dries up near Crni Kuk. Sinking waters are directed towards the zone of concentrated flow in the area of Rilja. Downstream does not have flow. In case (B), Zalomka flows to the Rilja ponor zone but also downstream from this zone. This part of the flow is formed by springs downstream of the ponor zone. The springs near Šnjetica, temporarily active, form a smaller short-term flow towards the Rilja ponor zone. In the ponor zone, there is no flow. Sinking water flows toward karst channels in the zone of concentrated flows. Situation (C) is common in the wet period. The surface flow is continuous and the ponor zone is maximally active, but this is insufficient to receive all flowing water from the Zalomka riverbed. On the Šnjetica dam site, upstream from the village of Kifino near the temporary spring, six exploratory boreholes were drilled, with a depth of 120–241 m. Geophysical radioactive logging of these boreholes and geoelectric sounding and profiling was carried out. At the same time, the reservoir area was also investigated in detail. Due to high water permeability between Rilja and the Šnjetica dam site, this dam site is abandoned. By dye tracing of the ponor in the riverbed of Zalomka near Kifino Village, the connection with the Buna Spring was established. In the part of the Zalomka riverbed between Ovčiji Brod and Budisavlje, dye tracing of borehole T-3 and the Ždrebanik estavelle was carried out. In both cases, a connection with Buna Spring was established. To analyse hydrogeological properties, i.e., waterproofing, there was investigation of the Zalomka riverbed downstream of Ovčiji Brod and Budisavlja. Investigations in the area of the so-called Žiljevo limestone ridge, showed limestone paleo-relief below the Promina formation is in a few localities near the village of Žiljeva. There were six investigation boreholes drilled to the following depth: F-1 = 183 m, F-2 = 285 m, F-3 = 300 m, Ž-4 = 301 m, F-5 = 300 and F-6 = 360 m. Three boreholes were drilled in the area of Trtine: T-1 = 156 m, T-2 = 205 m and T-3 = 122 m, and in the bed of Zalomka near Budisavlje: B-1 = 93 m, B-2 = 83 m, B-3 = 100 m, B-4 = 100 m and B-5 = 100 m. The data from the O-1 borehole near Odžak are interesting. It is 205 m deep. Up to 162 m is Promina formation, and from 162 to 205 m is limestone. It passes the 75th meter

2 Catchments, Surface Flows Springs

through two marl zones, with a thickness of 15 and 28 m (43 m in total). From 75 to 162 m, it passes through four zones of marl thickness of 3, 4.5, 9.5 and 16 m (33 m). Total thickness of marl at this location is 76 m. This is the largest thickness of marl established by drilling in Nevesinjsko Polje. In this area, more tracer experiments were done, which all showed that water that sinks along the bed of Zalomka, downstream from Ovčije Brod, passes through the Žiljevo limestone ridge and flows towards Buna Spring. Tracer dye testing of the Ždrebanik estavelle was done three times. In the first test (J. Mladenović, Energoinvest, 1961), the connection with the Buna Spring was established. The test was repeated in 1969 (HET, Lj. Jadrijević), when the bed of the Zalomka River near the village of Kiffino was dry. The day after the dye injections, a huge rain occurred. The dye from the underground discharged back into the Zalomka riverbed through the Ždrebanik estavelle and through the temporay springs along left river bank, 200 m upstream. The dye test was repeated on 8/10/1969 (HET, L J. Jadrijević), when the connection with the Buna Spring was confirmed. In order to define the depth of the karstified zone with active channels, isotope J-131 was used. Two injections of J-131 were done, and observation points were boreholes in the area of the Žiljevo limestone ridge. An isotope was injected into the Bogodol Ponor (June 18, 1970, 1.5 Ci), and the radioactive labeled wave was detected in borehole Ž-3 at a depth of 220–222 m (Fig. 2.30). An increase of radioactivity was registered in the water of Buna Spring on 27.06.1970. The next time, isotope J-131 was injected in Ždrebanik on 01.07.1970. (approximately 2 Ci) but, due to jamming of the probe used for measurement of radioactivity in the borehole, investigations were stopped. Four boreholes (P-1 to P-4) were drilled at the Pošćenje dam site. In the area of Grebak, upstream of the Biograd Ponor in the Promina conglomerates, several sinkholes were registered that are more than 100 m away from Zalomka (Fig. 2.31). In order to determine the hydrogeological characteristics of this part of the left bank, four boreholes were drilled (ZB-1 to ZB-4). In one of the ponors on the Grebak area, dye was injected twice in 1978 (in May and December). Both times, 60 kg of Na-fluorescein was injected but, in spite of several months of observations on a large number of downstream springs (including springs in the Neretva and Bregava valleys), the presence of tracer was not found in even one sample. Since it was estimated that the Grebak area could represent potential problems for permeability of the future reservoir, it was decided (1987) to shift the dam site upstream. An appropriate investigation program was proposed for the new dam site location.

2.1 Water Catchments and River Flows of East Herzegovina

Fig. 2.30 Variation of radioactive intensity in pieyzometric borehole Ž-3 when the water wave containing the isotope J-131 passed through the karstified zone at a depth of 221 m. (1) Increase in radioactivity intensity (2) Natural radioactivity (Milanović, 1979)

2.1.17 Drežanjka Creek and Zovidolka River The Drežanjka creek and the Zovidolka River are the left tributaries that merge with the Zalomka River, close to the village of Zovi Do.

Fig. 2.31 Dam site Pošćenje. 1. Large ponor, 2. Ponor, 3. Borehole, 4. Cretaceous limestone, 5. Promina conglomerates (Milanović, 2006)

139

In valley of the Drežanjka creek there is one dry cave in the spring zone and two caves in the middle part of the creek, from which a large amount of water dischages during a period of rainfall. During the investigation of the water capacity of the valley, it was determined that one of the mentioned caves is longer than 200 m but has not been fully explored. The spring itself is situated in conglomerates in the shape of a typical karst eye. The valley of the Zovidolka River, which is cut into the conglomerates of the Promina formation, has all the characteristics of a typical karst valley. It emerges from a temporary siphonic spring, Jama, near the village of Udbina. The spring is created on the contact between Eocene flysch and conglomerates. Up to now, hydrogeological works show that the catchment of karst aquifer of the Jama spring covers the area of Slato Polje, and it may also cover part of the Bjelasnica Mountain. One dye test in the bifurcation zone close to Gatačko Polje indicated this possibility (mentioned earlier was dyeing near Rašćelica, 6 km from Nadanić). According to laboratory analyses, the presence of dye was indicated in one water sample from the Zovidolka River. In the sample, taken a day earlier, there was a possible but questionable presence of dye. Since the presence of dye was determined in the last sample, this result is not accepted as authoritative enough for conclusions. According to this result, the dye traveled for 436 h. The marked wave covered a distance of 17,900 m while moving at a velocity of 1.14 cm/s. The east catchment of Jama Spring borders with the catchment of Trebišnjica and Lukavačko Polje (catchment of Bregava) to the south, with the catchment of Dabarsko Polje (Bregave), and toward the north and west with the Zalomka catchment, i.e., with the Buna and Bunica catchments; alone, it belongs to the catchments of both these springs.

140

2 Catchments, Surface Flows Springs

Next to the Jama Spring, through which about 80% of the water is discharged, the spring zone stretches along the Zovidolka riverbed for a length of approximately 3.5 km and consists of the Pećina, Brusac and Milosava springs. In a dry period, it does not discharge in any of these springs. The flow of the Zovidolka varies from 0.00 to over 20 m3/ s. Average annual flow ranges between 0.63 and 1.19 m3/s. Surface flow greater than 20 l/s exists between 275 and 351 days per year. When the inflow from the aquifer to the outlet of the spring zone is reduced to a minimum, surface flow stops, but not underground circulation, which continues along the flysch—Promina contact zones. These waters flow along the Zovidolka valley, through tectonised and karstified conglomerates below the bottom of the riverbed. When they reach the ponor zone in the downstream flow of the Zovdolka River, they sink and flow towards Buna Spring.

2.1.18 Zovidolka Spring: Jama Jama Spring is located approximately 6.5 km upstream from its mouth in the Zalomka River. The spring zone is formed in Promina conglomerates at the contact zones with flysch formations. This is a siphon kind of spring, whose channel was explored by divers for a length of 60 m, to a depth of 20 m. More details of the morphology of this siphon is given in Chap. 3, Speleological Facilities. In September and October of 1986, a pumping test of the submerged karst channel was performed. Since the previous 2 months in this area were dry, without precipitation, and there was no natural discharge from the spring, it is certain that the results of the pumping test provide meritorious data about the capacity of this spring in the dry period. In the course of these investigations, 26,647 m3 of water was extracted in total from the Jama Spring. This pumping test proved that, with a lowering of 44 cm, approximately 25 l/ s of water can be pumped from this outlet, which represents part of the dynamic water reserves of this aquifer. If the amount of pumping is greater than 30 l/s, the level decreases permanently. This means that, excepting dynamic reserves, a part of the static reserves of this aquifer were also pumped. After the pumping stopped and the level recovered, an interesting phenomenon was observed. During recovery, the level rises above the initial level by 130 cm (Fig. 2.32). This phenomenon is a consequence of the kinetic energy of the water mass in the karst aquifer, which has been launched due to the level difference between the piezometric line in the aquifer and the depression level in the karst channel. Technically and economically, the most acceptable solution proposed is well type collection, which consists of two wells with a depth of approximately 45 m and a diameter of

Fig. 2.32 Jama Spring, graph of pumping test (Milanović & Jokanović, 1994)

444 mm. This diameter enables installation of a well structure of 300 mm and submersion of deep pumps with a capacity up to 50 l/s.

2.1.19 Jedreš and Jezduš Springs Both springs are situated close to the Nevesinje urban area in Promina conglomerates (Fig. 1.95). Jezduš Spring is located in the foothills of Gradina, at an elevation of 1050 m. On the slopes, immediately below the entrance to the cave, there is an old tapping structure, from which drinking water was supplied to town of Nevesinje. This structure is not operational. Jedreš Spring is located on the outskirts of Nevesinje, at an altitude of 904 m (Fig. 2.33). This is the final part of local basic karst flow, through which the aquifer discharges, with limited saturation capacity. This karst channel is formed in Promina conglomerates. A fissure-karst porosity system, with relatively good retardation capacity, is drained through it. Discharge varies between Qmin 20 m3/s. The spring is tapped for water supply for the area of Dubrovačka Župa, from the Kupari to Cavtat town, and the settlements between Močići and Ćilipi. The pumping capacity of the spring is Q = 150 l/s; however, the maximum estimated capacity in a dry period is Q = 250 l/s.

Catchment Area of Duboka Ljuta Spring Most of the waters of Duboka Ljuta Spring originate from the waters of its own catchment, and a smaller part discharges at the spring as a consequence of seepage from the head race tunnel of HPP Dubrovnik. Determination of catchment area sizes is very complicated. The most significant concentrated infiltration zone is situated in the northern part of the catchment area. This is the ponor (estavelle) zone of Mokro Polje, including the estavelle in the left bank of the Gorica Reservoir. By dye test of the ponor in the tunnel from Gorica—Plat (head race tunnel of HPP Dubrovnik), on the chainage 0 + 216, the connection with the tail race tunnel II of HPP Dubrovnik was established. By tracer tests of Trap and Trnje ponors in Mokro Polje, the existence of good hydrogeological connection between this part of the catchment area and the spring zone was established. The labeled wave velocity ranges between 3.15 and 4.70 cm/s. This velocity is higher than the average velocity of underground circulation in the dinaric karst. It takes from 2.5 days up to 4 days for water to travel this distance from the ponor zone to the springs. It is certain that waters when reach the ponor (estavelle) zone in the lowest part of Mokro and Abatno Polje flow towards Robinson. The question is how many and which waters of this poljes are coming to these zones. Because of complicated natural conditions the answer on this question became even more difficult after a series of technical interventions that were carried out during construction of the Trebišnjica Hydrosystem. These are primarily the

2.2 Springs of Dubrovnik Littoral and Neretva Valley

pipeline for HPP Dubrovnik with culvert and drainage canals. These structures have been extended several times and considerably changed runoff conditions. Most of the losses from the head race tunnel flow towards Robinson, and a smaller part flows towards Zavrelje. Depending on the current condition of the lining, losses from the tunnel vary between 0.2 and 1.2 m3/s. The surface of the catchment area of Duboka Ljuta Spring is estimated at approximately 60 km2.

2.2.6

159

Towards the east, the catchment area is bordered by the catchment areas of several springs in the Boka Kotorska Bay, and toward the north to the catchment of Oko Spring. Toward the west, the catchment borders with an area that belongs to Robinson Spring. Watershed of the catchment area is approximate in estimated size and can be subject to correction. So, for example, the larger part of the area along the northern edge of Konavosko Polje is divided between the catchments of Konavoska Ljuta and Robinson springs. It is certain that part of the water from those areas also feeds numerous small sources along the edge of the polje.

Konavoska Ljuta

Hydrogeological Characteristics Konavoska Ljuta is the most significant spring in Konavosko Polje. The spring zone is formed in head area of the High karst overthrust, i.e., on the tectonic contact of Eocene flysch and carbonate Mesozoic complex (Fig. 1.29). The spring zone consists of several closest discharge points. The entire zone is buried by large blocks and is overgrown by vegetation. The discharging area is situated between 80 and 90 m a. s.l. In the entire area of this spring zone are the remains of old water intakes and several independent water supply systems for irrigation. Hydrological Characteristics Because Konavoska Ljuta has characteristics of a seepage spring, it is not simple to organize observations of discharge. For this reason, the first WGS (1957) is located near the bridge, downstream from the spring zone. Level zero of this WGS is at 55.76 m above sea level. Since part of the water flowed outside the control of this WGS, a hydrological station was constructed 2 years later in the canal for irrigation of the supplementary station, with an elevation of 0 = 55.49 m. Both of these stations were abandoned on 31.12.1974, as there was a new station—Dvori. Zero level of new WGS is 0 = 69.96 m a.s.l. From 1988, the station has been equipped with a limnigraph. Spring discharge 1957–1966 varied between: Minimal measured flow, Qmin = 0.2 m3/s. Maximum measured flow, Qmax = 26 m3/s. Catchment Area of Konavoska Ljuta Spring The catchment of Konavoska Ljuta covers the eastern part of Konavosko Polje and extends to the Zupci plateau and the western slopes of Orjen Mountain. The surface of this catchment area is 90–100 km2, and the highest parts of the catchment are above an altitude of 1000 m. Only one tracer test was done in the catchment area. The shaft of Bravenik was investigated by dye tracer in 1971. Toward the Konavoska Ljuta, the velocity of the labeled wave flows with an average velocity of 0.53 cm/s.

2.2.7

The Other Springs of Dubrovnik Littoral

Springs of Slano Area Permanent springs in the area of Slano are mostly of small discharge. The more significant springs registered are Ugor, Skok, Usječenik and Luncijata. Ugor is the most important spring in Slano. It is located in the village of Grgurići. The spring is remote, approximately 100 m from the seacoast. A hydrological station was established at this spring in 1963, for construction of the Trebišnjica Hydrosystem. Zero of WGS is 0 = 0.33 m a.s.l. In the dry period, the yield decreases below 1 l/s. Ugor spring was observed during all tracer tests in Popovo; however, only connections with Popovo Polje are established. This connection was established with tracer tests of the Mlin-Bandera Ponor near Velja Međa. Skok was formed at the contact of Triassic dolomitic limestones and Eocene flysch. It belongs to the group of contact-descending springs. It is a temporary spring of very small discharge. Usječenik is located south of the town of Slano, at an altitude of about 60 m below the main road, toward the sea. It is formed on the contact between dolomitic limestone and Eocene flysch, and belongs to the group of contact descending springs. In the dry period, the yield drops to 0.5 l/s but never dries up totally. The spring is tapped for local use. Luncijata is located on the seacoast, in the bay next to the church of St. Luncijata. This spring is of the fissure type and was formed in Eocene limestones. According to the data of the Institute for Geological Research from Zagreb, on December 10, 1981, discharge was 50 l/s, and on April 7, 1982, it was 20 l/s. It is not known that the spring has ever dried up. The water is brackish and, in the dry season, salinity significantly increases. The main tapping structure in the area of Slano is the so-called “new intake structure” which consists of two drilled wells that were drilled in 1970. Both wells are located in flysch, and their waterbearing parts are in karstified limestone. The depth of one well is 80.5 m (elevation of the

160

terrain is 33.75 m above sea level), and the other is at 178.00 m (elevation of the terrain is 24.97 m). During the period of operation, both wells showed some other characteristics in relation to experimental pumping. It showed that 8 l/s can be pumped from both wells without a significant increase in chloride content, except in the dry period, when the amount of chloride in the water increases up to 500 mg/l at a capacity of 8 l/s. The paradox is that in the winter, after big and sudden precipitation, the intensity of salinity increased sharply in both wells (according to information from the employee who maintains the tapping structure). Springs in Trsteno (Vrba, Bare, Studenac and Bjelica) have small discharge during the dry season (Bjelica dries up) and were tapped for the needs of the settlement. Minimal discharge is less than 2 l/s. In the village of Orašac, these are the recorded springs: Pod Platanom, Doline and a spring near a small reservoir in the dolomites above the village. At a minimum, the discharge of these springs is not larger than 1–2 l/s. These springs serve as the water supply for the Orašac settlement. Above Mali Zaton, at an elevation of about 130 m (contact flysch-dolomite), there is a temporary spring that is tapped and used for the water supply for Zaton in the winter. In the Dubrovnik River (area of Dračevo village and Prijevor), there are two tapped springs whose minimum discharge is not more than 2 l/s. Maximum discharge of the spring near Prijevor is about 20 l/s, and of the spring in Dračevo village is 7–10 l/s. The spring of Račevica is located east of Ombla, in the area of Šumet, northwest of the Slavljan Spring. It is formed on the tectonic contact of Eocene flysch and Upper Triassic dolomite. It belongs to the group of contact descending springs. At one time it was incorporated into the system of ancient Onofrio water tapping structures for Dubrovnik water supply. The Račevica Spring has a discharge of 0.2–0.4 l/s and is tapped. Below the spring, there is a landslide on flysch slopes. Apart from Račevica, there are several smaller springs between Ombla and Slavljan—Čajkovica, Bota and Knežica. They were all formed along the same tectonic contact, with discharge up to 0.2 l/s. Most of these springs, including Slavljan, were captured by Andriuzzi de Bulbito and Onofrio della Cava for water supply for Dubrovnik in 1436/37. The water canal to Dubrovnik, 11,700 m in length, had a capacity 70 l/s. There is a etailed explanation in Sect. 4.10. The Slavljan belongs to the Ombla catchment area. It is located near Šumet. It was formed on the tectonic contact of Eocene flysch and Mesozoic carbonate complex. It is located at an altitude of 108 m. It is a temporary spring whose is activ

2 Catchments, Surface Flows Springs

only in a particularly wet period of the year. This spring is part of the karst system of the earlier phases of karst evolution of the Ombla Spring aquifer. Now, it functions as overflow when the Ombla aquifer is fully saturated and when its level reaches an elevation of 130–140 m. A hydrological station was established by the Trebišnjica Hydrosystem in 1982 and was later equipped with a limnigraph. Maximum discharge is around 2 to 3 m3/s. There is a particular group of springs in Dubrovačka Župa, from Brgat to the village of Petrača—Smokovac, Vrelo, Pješine, Bravinjac, Suđurac, Dizin, Žeginac, Petrača and Skoračica. All of these springs have water from small and local catchments which exist between the Ombla and Zavrelje catchment areas. Under certain hydrogeological conditions, probably, they enter into peripheral parts of these catchments. Except for Bravinjac other springs in the village of Martinovići, Suđurca in Postrana and Smokovac and Ledine near Brgat, which never dry up, all of the other springs are temporary. Between Zavrelje and Robinson, next to the main road, there is the Smokovljenac Spring. It was formed at the contact of the Eocene flysch and the Mesozoic carbonate complex. With a yield of 2–80 l/s, it could be interesting to consider the possibility of tapping. This spring is permanent. It was equipped for hydrological monitoring and was monitored for a short time. The group of springs belonging to the western part of Konavosko Polje consists of Klimor, Dobra voda, Mala voda (Smokovjenac), Šišina voda, Lisica, Gođej, Umnjak, Dragovine, Bodre and Drimlje. All of these springs are situated northwest of the Konavoska Ljuta, in the areas of Drvenik, Mihanić and Pridvanje. They are located in Eocene flysch and diluvial deposits, under which is flysch. The basic characteristic for all these springs is predominantly small discharge; all are permanent and are tapped for the needs of nearby settlements. In the eastern part of Konavosko Polje, there are a large number of springs of varying discharge. They are located in the areas of Dunava, Dubravka, Dobruša and Vodovađa. Complicated tectonic relationships and diverse lithological composition conditions different discharge and spatial position of the springs. A number of springs are situated in flysch, and some are at contact flysch with limestones and dolomites. The springs with the largest capacity are tied to the wider zone of the regional Zupci fault. They recharge from Mesozoic carbonate complex along this fault, from the direction of Grab. The more significant of these springs are Vataje, Vodovađa, Vojska and Dajevik. The Vataje Spring is located between the villages of G. Vodovađa and Vataje, near the churches of St. Vid and St. Ivan. The spring is formed in Eocene limestones. It is partially tapped and serves as the local water supply, and part

2.2 Springs of Dubrovnik Littoral and Neretva Valley

161

Fig. 2.52 Submarine spring Likavica near Doli and temporary springs high above sea level 1971 (Photo Milanović)

of the water is canalled to nearby irrigation plots. According to the data of the Institute of Geology research from Zagreb, the discharge of the spring on 5.05.1982 was 20–40 l/s, and on 27.09.1983, the discharge was measured at 15–18 l/s. According to information from locals, it is not known that this spring ever dries up. Vodovađa Spring is located in the village of Upper Vodovađa, in Eocene limestone. The discharge of the spring varies between 4 and 25 l/s, but these quantities cannot be taken as absolute minimums and maximums. The spring is partially tapped for water supply and irrigation. Springs from Budima to the Neretva River Delta West of Slano bay, in the direction of Banić, Janska, Doli, Buda and Neum, there are not more significant springs. In this area, between the coast and Popovo Polje, there are nohydrogeological barriers which, by position, depth and continuity, can prevent direct circulation towards the sea on a wide front. A regional flysch barrier, which is a very efficient hydrogeological barrier from the Konavasko Polje to Zaton, has almost completely lost this function. Here, it is thin, insignificant, deep and, most importantly, demolished in a number of places with transversal tectonics.

That is why it is in the period from Würm maximum (when the sea level was 96 m lower from today, Šegota, 1982) until today that there was enough time for development of deep karstification along this part of the coast, with zones of deep discharge below the present sea level. As a result of deep karstification, there are active numerous submarine springs along this part of the coast in a period of precipitation. The largest number of submarine springs is registered in the bays of Janska, Budima, Doli and Bistrina. Between Janske and Doli 35 submarine springs are registered. The largest one is Likavica, near Doli, with an estimated maximum discharging capacity of over 10 m3/s (Fig. 2.52). In 1971, an attempt by divers to find the mouth of Likavica and to possibly access its channel was not successful. In a period of huge precipitation, the water discharges under pressure from cracks in the limestone along the coast, 5–10 m above sea level. It was determined by dye test that the larger part of the water in these submarine springs originates from the ponors between Sedlari and Provalija in Popovo Polje. Under natural conditions, large amounts of water flow from Provalija and the surrounding ponors in Popovo Polje toward Bistrina bay. Water discharges through the numerous

162

2 Catchments, Surface Flows Springs

Fig. 2.53 Neretva River Delta. Blue eye situated close to the eastern perimeter of the Neretva wetland, 2012 (Photo Milanović)

submarine springs and, after huge precipitation, from temporary springs along the northern rim of Bistrine Bay. That water is mostly brackish, with a high chloride content. The percentage of fresh water which then discharges out cannot be determined. The presence of submarine springs is registered in the bay near Neum. Submarine springs and brackish springs are not active in the dry season. There is the appearance of “Blue eyes” along the eastern perimeter of the Neretva River delta (Fig. 2.53). When the underground streams of East Herzegovina were investigated by tracer tests, first in Popovo Polje, with the use of large quantities of dye (often over 100 kg for each ponor), water samples were also taken from Modro Oko (Blue eye). Not even the smallest traces of dye were established in any of the samples.

2.3

Springs Along the East Rim of Neretva Valley

The waters of the Zalomka River, including the catchment areas of Nevesinjsko and Dabarsko Poljes (with a minor share of Fatničko Polje), and the waters that sink in the lowest part of Popovo Polje flow toward the springs along the regional erosion base of the Neretva valley. Buna and Bunica springs have the highest elevation (37 m), and the lowest and southernmost spring is Bađula Spring, close to sea level, at about +1 m a.s.l. Buna and Bunica springs represent one of the largest zones of concentrated discharge in the karst of Dinarides. The second largest zone of concentrated discharge is the Svitavsko—Deransko Blato (Hutovo Blato), at an altitude

2.3 Springs Along the East Rim of Neretva Valley

163

Fig. 2.54 Results of tracer test of the Ponikva Ponor in Popovo Polje (Milanović, 1971a)

of about +3 m above sea level. Springs along the eastern edge of the Neretva valley, near Metković, from Doljani to Bađula Spring belong to the third largest zone (Chap. 1, Fig. 1.42). The springs of the Bregava River also belong to the erosion base of the Neretva valley.

2.3.1

Springs Between Kuti and Dračevo

The most significant springs along the left rim of the Neretva valley, from Metković to Lake Kuti are Doljani, Šunjić dulo, Glušci (Straža), Billy Vir, Spile, Mlinište, Mislina, Bađula (Fig. 1.42). The springs are situated at elevations from +2.5 to +1 m. This is the same as the alluvial sediments of this part of the Neretva delta, which are under permanent influence of tides, so most of them are brackish in the summer. In a period of high tides there is infiltration of water into theopenings of some of these springs. All springs are connected to a large ponor zone in the lowest part of Popovo Polje. The largest ponors in this zone are Lisac, Ponikva, Žira and Kaluđerov Ponor.

The main directions, depth and velocities of the flow of these ponors are defined by tracer experiments, Na-fluorescein (Uranin) and radioactive isotope Br-82. During these investigations, a large number of piezometric boreholes were executed in the area of these ponor zones, for the needs of construction of the RPP Čapljina project. It has been established that Ponikva, Žira and Kaluđerov ponors belong to a single karst system that ends at the edge of the Neretva valley. Mostly, this system follows a dry karst valley, the former outflow of Popovo Polje, that is, the dry riverbed of former Pra-Trebišnjica: Hutovo—Donje Hrasno—Kolojanj—Neretva valley. Observations during tracer tests of Ponikva Ponor show specific sequences of labeled wave appearance (Milanović, 1971b). This is characteristic of most tracer tests of ponors at the very end of Popovo Polje (Fig. 2.54). Discharge of the labeled wave always has the same sequence of appearance on the springs, marked from 1 to 6. It can be seen that the labeled wave appeared first on the northern group of springs, in the order of Glušci, Šunjića Dulo, Bili Vir and Doljani, and then

164

2 Catchments, Surface Flows Springs

Fig. 2.55 Hutovo Blato wetlands. Position of important permanent springs (Milanović, 2009)

on Mlinište, Mislina and Bađula. The appearance of dye was not established on the one spring in Svitava. Flow velocities between ponor zones and springs in the Neretva valley (distance 16–20 km) vary between 150 and 300 m/h. However, in the part of flow trace immediately after sinking, gradients are very large, so in the first 1500 m the velocity is around 1600 m/h, and after 4300 m the velocity is about 1200 m/h. At that distance, the water went down from an elevation of 220 m to an elevation of about 140 m, and even at elevations of about 60 m. The need of water to reachthe level of base flow as soon as possible is reflected in an extremely large gradient immediately after sinking. This proves the data of numerous speleological investigations in karst of Dinarides, like thistracer test—(see Chap. 4, Sect. 4. 4.5, Hutovo Reservoir).

2.3.2

Springs of Hutovo Blato

The natural characteristics of the Hutovo Blato wetland are shown in Sect. 1.7. More than 70 springs have been registered in the territory of Hutovo Blato. Most of them (42) are active only in the wet period of the year. In the dry season, the discharge of permanent springs drops to a minimum of a couple of liters per second. The position of more significant permanent springs is displayed in Fig. 2.55. The westernmost spring zone forms Lake Škrka (Fig. 2.56a). Only one of these springs is permanent. Maximum discharge of this zone is estimated at 7 m3/s. The most significant springs along the northeastern rim of the Derane cryptodepression are Jelim, Jamica, Kučine, Drijen, and Orah. The springs with the highest (estimated)

2.3 Springs Along the East Rim of Neretva Valley

165

Fig. 2.56 Hutovo Blato. (a) Škrka Spring (b) Londža Spring, 2008 (Photos Milanović)

discharge of permanent springs (hot springs) are Jelim and Drijen. A small lake “eye” near Jelim and Drijen indicates deep circulation in part of the spring zone. Sublacustrine spring Jelim is a submerged sinkhole, with a karst channel at a depth of 6–10 m beneath sea level. Estimated maximum discharge of this sublacustrine spring is 7.7 m3/s. The most significant springs along the eastern rim of the Derane depression are Babino Oko (consists of more separated springs), Londža (Fig. 2.56b), two discharge places and Smokva and Gabeokino vrelo springs. As well as the mentioned source along the northern and eastern rim of Deranska Kaseta, numerous occurrences of water discharge were registered, when the Bregava flow is active along its entire length. A large part of the water discharges directly into the swampy part of the lake and

from the lake’s bottom (sublacustrine). Because of this, these phenomena are difficult to notice. Some of them are registered near Karaotok. By tracer test of borehole BR-1 in the Bregava riverbed, downstream from water gauging station Do, the connection with the Drijen Spring was established. The tracer test of Ponikva Ponor in Dabarsko Polje (1955) indicated a connection with Deransko Blato (Londža Spring). By the next tracer test of the same ponor, this connection was not confirmed. Towards Londža spring, water flows that sinks into the numerous ponors in the bifurcation zone of Popovo Polje near Velja međa. This is established by tracer tests of the Mill- Bandera, Doljašnica and Provalija ponors. The waters of these springs create Lake Derane and flow through the Krupa River into the Neretva (Fig. 2.57). The

Fig. 2.57 Hutovo Blato. (a) Derane lake (b) Krupa River, 2008 (Photos Milanović)

166

2 Catchments, Surface Flows Springs

Fig. 2.58 (a) Buna Spring (Photo Milanović, 1969) (b) Bunica Spring, 2006 (Photos Milanović)

minimum estimated inflow into Derane Lake is Q ~ 3 m3/ s and maximum is 42 m3/s (Bakula, 2009). In natural conditions, the Svitava depression was the largest temporary accumulation named Jezero (Lake). The springs of the Svitava depression are located along its southern rim. From the 26 registered springs, the more significant are Svitava (a large temporary spring), Trstenik, Njeginja, Živnjak, Smokovnjak, Ljubanovo vrelo, Sopot, Desilo, Lukavac, Ljubača and Crni vir. Maximum discharge of permanent spring Živnjak is a few cubic meters per second. This spring was captured for technical drilling water during investigation works for the RPP Čapljina. Some of the mentioned springs originally were submerged sinkholes, 9–10 m deep, with a sublacustrine spring at the bottom. The Svitava, Sopot and Lukavac springs are connected to the bifurcation zone near Velja Međa but also with the downstream ponors Crnulja and Lisac in Popovo Polje. But, while the waters from Crnulja Ponor flow exclusively towards the Svitava depression, the waters of Lisac appear in the Doljani Spring in the Neretva valley, except for discharges through the springs.

2.3.3

Buna and Bunica Springs

The springs of Buna and Bunica are formed on the eastern edge of the Mostar Polje, at an altitude of about 37 m (Milanović, 2006; Stevanović, 2010). Although they are only 4 km apart, there is no hydrogeological connection between them. The Buna Spring is certainly one of the most famous and attractive springs in the karst of Dinarides (Fig. 2.58a).

Basic hydrological characteristics of Buna Spring discharge regime at the WGS Blagaj 1967—to 1984 are: Average flow, Qav = 23.70 m3/s Minimum flow, Qmin = 2.95 m3/s Maximum flow, Qmax = 380 m3/s Basic characteristics of the hydrological regime of Bunica Spring (Fig. 2.58b) at the WGS Malo Polje 1972 to 1984 are: Average flow, Qav = 20.25 m3/s Minimum flow, Qmin = 0.72 m3/s Maximum flow, Qmax = 207 m3/s Both of them belong to the group of karst springs with deep siphons. According to Franch cave diver C. Touloumdijian (2001), the karst channel has been investigated to a length of 520 m of the Buna siphon (Fig. 2.59). The depth of the investigated part of the siphon is -68 m, measured from the entrance level. The sunken part of the Bunica channel is 160 m in length, and the investigated depth (siphonic) is 73 m (Fig. 2.60). In addition to the French divers, speleologists E. Humo from Mostar and S. Milanović from Belgrade also participated in this research (Fig. 2.61). Both springs are characterized by large flow variations and extremely high maximum discharge. In January 1971, the discharge of Buna Spring was registered at Q = 380 m3/ s (Fig. 2.62). Demarcation of the catchments areas between Buna and Bunica springs is extremely complicated, practically impossible, so they are treated here as a single catchment. The discharge from Buna Spring is controlled at the WGS Blagaj,

2.4 Characteristics of Large Ponors and Ponor Zones

167

Fig. 2.59 Buna Spring. Siphonal section of Buna outlet (Touloumdijian, 2005)

and discharge from Bunica Spring is controlled at the WGS Malo polje. Total flow of these springs is controlled at the WGS Buna, before the confluence with the Neretva River. The surface catchment area of Buna Spring (WGS Blagaj) is estimated at about 1100 km2. This regional catchment consists of: – the catchment of Zalomka River, from the watersheds of Gatačko Polje to the Biograd Ponor. – the northwestern part of Nevesinjsko Polje, with the largest ponors being Ždrijelo, Babova Jama and Zlatac. – the central part of Nevesinjsko Polje, south from the Nevesinje—Kifino Selo road. – the water that gravitates toward them and sinks along the Zalomka riverbed, from Kifino Selo to Ljeskovik, and, the water that sinks along the Zovidolka riverbed before merging with the Zalomka River (estavelle Ćetanuša), as well as the water that sinks at the area of the Krupac Ponor at Trusina Mountain, south of Snježnica Mountain.

– the large mountainous area between the Nevesinjsko Polje and springs (Buna and Bunica), and the massif Podveleža and parts of Velež Mountain, including Gornje Zijemlje (Hansko Polje), which also belong to this catchment area. Since certain peripheral parts of the catchment area are located in bifurcation zones, it is clear that the surface area of the Buna/Bunica catchment can be possibly subject to correction. Retardation capabilities of the part of aquifer that is depleted via Buna Spring, which is formed in the area of the polje itself, are better compared to a typical karst aquifer. It is one of the most significant aquifers in the karst of the Dinarides. Undoubtedly, the large minimal discharge of Buna Spring is a consequence not only of the size of the catchment area but also of the significant retardation capacity of the large mass of Promin sediments, as part of Nevesinjsko Polje and Trusina Mountain. Bunica spring represents the end of the underground river Zalomka, after which it sinks into the Biograd Ponor. Important hydrogeological characteristics of the karst aquifer of Buna and Bunica springs are presented in Nevesinjsko Polje, Sect. 1.6.11.

2.4

Fig. 2.60 Bunica Spring. Siphonal section of Bunica outlet (Touloumdijian, 2005)

Characteristics of Large Ponors and Ponor Zones

The most significant zones of concentrated infiltration with a large absorption capacity are usually located in the lowest parts of karst poljes, such as: the Biograd ponor in Nevesinjsko Polje; the Srđevići—Šabanov ponor zone, with huge ponor zone Jasikovac/Vranjača in the Malo Gatačko Polje; Ključke Rijeke Ponor (Ključki Ponor), with Jasovica Ponor in Cerničko Polje; Pasmica Ponor zone in Fatničko

168

2 Catchments, Surface Flows Springs

Fig. 2.61 Cave divers investigate Buna Spring, 2005 (Photo E. Humo)

Fig. 2.62 Discharge graph of Buna Spring, December 1970 to July 1971 (Milanović, 2018)

Polje; Ponikva—Kuti ponor zone in Dabarsko Polje and Popovo Polje, practically the whole length. Significant ponors but with less impact on regional hydrogeological and hydrological characteristics are: Ljeljinačka cave and Bobotov’s cemetery on the northeastern edge of Gatačko Polje and Krstac dry valley; Mlinica Ponor

in Lukavačko Polje; Mlinica Ponor in Slato Polje; Ždrijelo, Babova Jama and Zlatac in Nevesinjsko Polje; Konac in Ljubinjsko Polje and the Ždrijelovići ponor zone in Ljubomirsko Polje. A large number of ponors and ponor zones are also registered along the riverbeds. The most significant estavelle zones are Dračevo—Strujići along the

2.4 Characteristics of Large Ponors and Ponor Zones

northern edge of Popovo Polje and the area of Bugovina— Zgonjevo in Mokro Polje. Ponor Biograd is one of the largest individual ponors in the karst of the Dinarides and surely is the ponor with the largest swallowing capacity in Eastern Herzegovina (Figs. 1.101 and 1.102). The ponor is directly connected with Bunica spring. Zero level of the WGS is 0–799.90 m a.s.l. The measured swallowing capacity of this ponor is 86 m3/s. Maximum capacity is not measured because the ponor is submerged. By analyzing the discharge curve of the retention formed above the ponor, it was estimated that the maximum capacity exceeds 110 m3/s (Fig. 1.102). Water sinks into the ponor an average of 210 days. Given that, up to an elevation of approximately 815 m above sea level, the water is still in the riverbed of the Zalomka (Kolješka River), flooding begins only when flood waters rise above this elevation. In this case, the average duration of the flood is 37 days. A portion of the inlet channel is shown in Figs. 1.101 and 3.21. The ponor zone of Malo Gatačko Polje stretches along the southern edge of the polje, from Srđevića to Šabanov Ponor, at a length of 8 km, with a difference of approximately 6 m. More than 25 ponors and ponor zones are registered. Ponors with the largest swallowing capacity—Vranjača and Jasikovac (Fig. 1.96)—become active only when flood levels in the lowest part of the polje reach approximately 3 m. In a period of sudden inflow into these ponors and fast saturation of their channels, a huge quantity of air is squeezed out, followed by strong sound effects (eruption of squeezed air and local seismic shocks). The Srđevići Ponor, at the entrance to the Srđevići gorge, in periods of extreme precipitation is active in the regime of estavelles for a short time, that is, it discharges water. Natural swallowing capacity of the ponor has been significantly reduced as a result of the operation of the Gacko coal mine. At maximum flood, the backwater reaches the Srđevići gorge. Cumulative swallowing capacity of all ponors in Malo Gatačko Polje is about 160 m3/s. The ponor zone of the Cerničko Polje, with a large sinking capacity, was formed along the southern rim of the polje. The largest is Ključki Ponor, with a swallowing capacity of 15–20 m3/s (Figs. 1.87 and 1.88). When the discharge of Vilina Pećina Spring (max 50–60 m3/s) surpasses the swallowing capacity, retention over the ponor is created, and overflow toward the lowermost part of Cerničko Polje occurs. This is the period when the Stepenečki stream brings a considerable quantity of water into the polje. Other ponors are then activated, the most significant being Jasovica and Šukovića Ponors. The main ponors in Dabarsko Polje are Ponikva and Kutske Jame. Maximum cumulative swallowing capacity of ponors in Dabarsko Polje is about 45 m3/s (Figs. 1.80 and 1.82).

169

Ponikva Ponor consists of two close cave openings (Fig. 1.80). Swallowing capacity in the unsubmerged state (free surface flow) is up to 10 m3/s. In the case of high flood water levels (when the ponor is submerged and under pressure), swallowing capacity increases to three times higher quantity. During heavy rainfall, Ponikva Ponor can be in spring regime for a short time. According to Avdagić and Kovačina (1973), Ponikva Ponor swallowed a maximum of 30.2 m3/s in 1969/70. According to the same authors, in a period of heavy rainfall, outflow of 12.6 m3/s was measured from Ponikva Ponor. It was determined by these researchers that an unequivocal relationship between outflow from Dabarsko polje and discharge of Bregava does not exist. In Fatničko Polje, the majority of ponors are registered along the southern edge of the polje. The most significant is the ponor zone in the area of the largest ponor, Pasmica, in the Fatničko Polje, in the southeast part of the polje (Figs. 1.63, 1.64 and 1.67). Pasmica is the end of the stream formed by Obod and Baba Jama temporary springs. It consists of a vertical channel with a depth of about 25 m and a section between 4 and 10 m2. The channel continues towards the south, almost horizontally, to turn west after about 30 m (Fig. 2.63). About 40 m of the channel has been speleologically explored. For investigative purposes, when the polje is under water above Pasmica, an assembly tower with tracer injection pipes and a launching tube for a geo-bomb were constructed. Using a geobomb, the channel of Pasmica was followed to a distance of 135 m (azimuth 112°). According to data presented by Energoinvest, maximum swallowing capacity of this ponor is about 20 m3/s. The cumulative capacity of all ponors and estavelles in Fatničko Polje (at maximum flood of 38 m) is about 120 m3/ s (Fig. 1.8). It is important to note that the sinking capacity changes, depending on the intensity of rainfall in the catchment area and, more recently, is partially affected by level of the Bileća Reservoir. In a period of extremely high groundwater levels, when all ponors are in the regime of springs, inflow into the polje is almost twice as large as when it exclusively absorbs water (Avdagić & Kovačina, 1973). According to Avdagić (1973), in 1971, out of the 100 days that the field was flooded, the ponors were in the regime of springs for 16 days, and there was neither inflow nor outflow for 4 days. Immediately nearby to Pasmica, there are about 30 individual ponors registered, but every crack in a rock mass on the greater part of the southern slope above Pasmica also represents a place of sinking. Ponors of Popovo Polje. Popovo Polje is mentioned as one of the world’s largest ponor areas in several places in the preceding text. Through more than 500 registered ponors (Fig. 1.31) sinks over 250 m3/s. Into the greatest ponor in Popovo Polje, Doljašnica, sinks >55 m3/s. At this amount,

170

2 Catchments, Surface Flows Springs

Fig. 2.63 Pasmica Ponor, Fatničko Polje. 1. Special tower for investigations during flood season, 2. Pipe to insert the geo-bomb into the ponor, 3. Concrete foundation for tower structure, 4. The main opening of Pasmica Ponor

the ponor becomes submerged and, under these circumstances, further measurements of swallowing capacity become impossible. A more detailed description of the ponors and ponor zones in Popovo Polje is given in the chapters Popovo Polje (Sect. 1.6.1) and Characteristics of the Trebišnjica River (Sect. 2.1.11).

References Aranđelović, D. (1960). Geophysical Report. Geoelectrical investigations at area of Power Plant Dubrovnika. Institute for Geological and Geophysical Investigations. Belgrade. In Serbian. Aranđelović, D. (1966). Geophysical methods used in solving some geological problems encountered in the construction of the Trebišnjica Water Power Plant. Geophysical Prospecting, XIV(1). Belgrade. Avdagić, I., & Kovačina, N. (1973). Experimental determination of parameters for water balans in karst. Institute for hydrotechnic, Civil Engineering Faculty in Sarajevo Serbian. Bakula, E. (2009). Nature Park “Hutovo Blato” - hydrologic study. European Policy Programme. Barbalić, Z. (1978). Efects of construction of daily reservoir “Svitava” on solution of water management problems in the area of the lower Neretva River. Proccedings: Conference on influence of man made reservoirs on environment. Yugoslav Commiittee of Lage Dams (JKVB). JKVB and HET. Bonacci, O., Fumet, M., & Šakić-Trogrlić, R. (2014). Analysis of Ombla spring resources. Hrvatske vode. In Croatian. Zagreb, 22(88), 107–118.

Buljan, R. (2001). Robinson spring, (Duboka Ljuta spring). Geological Istitute of Croatia. Cvijić, J. (1985). Karst, geographical monography. Beograd. (Version in Serbian of Cvijić’s doctor theses under title Das Karstphänomen, Vienna 1983). Garašić, M., Krpina, I., Garašić, D., & Gospodinović, T. (1999). Investigation of less known caves in Dubrovnik littoral at last 20 years. Proceedings: Conference of Croatian speleologists, Ćilipi, Croatia. In Croatian. Gavrilović, D., & Lj. (1985). The intermittent spring Zaslapnica. Bulletin of Serbian Geographical Society. Tome LVIII. No 2, Beograd. Hydrosystem Trebišnjica. (1967). Hydro Power Plants on Trebišnjica River. Trebinje. Petrović, D. (1955). Dejan’s cave (Speleological and hydrological investigations on Trebišnjica spring). Institut for karst investigations “Jovan Cvijić. Milanović, P. (1971a). Upgrade of Klinje Dam. Geology, Investigation works. Documentation of HET. Milanović, P. (1971b) An attempt at define the routes of the karst system of Ponikva in Popovo Polje. Bulletin Scientifique, Section A - Tome 16, No 3/4, JAZU, Zagreb. Milanović, P. (1977). Hydrogeology of the Ombla Spring drainage area. Herald Geological. Sarajevo. In Serbian. Milanović, P. (1979). Karst hydrogeology and methods of investigation (302 p). HE on Trebišnjica. Milanović, P. (1981). Karst Hydrogeology. Water Resources Publication. Milanović, P. (1985). Possibilities of construction of underground reservoirs in karst. Scientific Conference “Water in Karst”, Mostar. Milanović, P. (1986). Palata Spring. Tapping structure. Design. Institute for Utility and Protection of Karst Water. Milanović, P. (1990). Sanitary protection zones of tapping springs for Dubrovnik littoral water supply. Hydrogeological Report. Energoproject Belgrade. Not published. In serbian.

References Milanović, P. (1992). Hydrogeological characteristics of geosyncline karst aquifers with an example of the Trebišnjica catchment. In H. Paloc & W. Back (Eds.), Hydrogeology of selected karst regions. International Association of Hydrogeologists. Milanović, P. (2009). Study on Hydrogeology of Nature Park Hutovo Blato. WWF European Policy Programme. Milanović, P. (2021). Karst of Eastern Herzegovina and Dubrovnik Littoral (2nd ed.). BINA. In Serbian. Milanović, P., & Jokanović, V. (1987). Tapping of spring under influence of sea tide. Proceedings: IX Yugoslav Symposium on hydrogeology and engineering geology. Priština. Milanović, P., & Jokanović, V. (1994). Some experience of water tapping in karstified conglomeraes of Nevesinjsko Polje. Proccedings: X Yugoslav Symposium about hydrogeology and engineering geology. Kikinda. Serbia. Milanović, P. (2006). Karst of eastern Herzegovina and Dubrovnik Littora (1st ed.). In Serbian. Beograd. Milanović, P. (2018). Engineerin Karstology of dams and reservoirs (354 p). CRC Press.

171 Milanović, S., & Vasić, L. (2022). Review of karst aquifer regime induced by surface reservoir in karst – example of Bileća Reservoir (Eastern Herzegovina). Proceedings. XVI Serbian Symposium on hydrogeology. Zlatibor (pp. 355–358). Radulović, M. (2000). Karst hydrogeology of Montenegro. Institut for geological investigations of Montenegro. Book XVIII, Podgorica. Šegota, T. (1982). Sea water level and vertical fluctuation of Adriatic Sea bottom from Riss-Würm interglaciation till today. Geology Heralld, 35(str. 93). Šimunić, Z., & Žibret, Ž. (1970). Design of reversible power plant Čapljina, Hydrology. Not published, Energoinvest, Sarajevo. Stevanović, Z. (2010). Case study: Major springs of southeastern Europe and their utilization. In N. Krešić & Z. Stevanović (Eds.), Groundwater hydrogeology of springs, engineering, theory, management, and sustainability. Springer. Touloumdijian, C. (2005). The Springs of Montenegro and Dinaric Karst. Proceedings of the International Conference Water Resources and Environmental Problems in Karst - Cvijić 2005, National Committee of IAH Serbia and Montenegro, Belgrade-Kotor.

3

Underground Morphology and Fauna

Vjetrenica Cave

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. Milanović, Karst of East Herzegovina and Dubrovnik Littoral, Cave and Karst Systems of the World, https://doi.org/10.1007/978-3-031-28120-4_3

173

174

3 Underground Morphology and Fauna

3.1

Speleology Facilities

3.1.1

Short History of Investigations

Caves are undoubtedly the most famous symbol of karst. They are one of the oldest habitats of people and animals and have become the subject of study in various scientific disciplines, as well as being utilized for tourist purposes. With the construction of large structures in karst, first of all dams and tunnels, interest in caves and caverns is become the domain of the engineering profession. When work on the Trebišnjica Hydrosystem first began, great importance was given to speleological investigations. One of the reasons for this was numerous problems and even failures in a number of facilities in karst terrains, due to in sufficient knowledge of underground morphology. Speleology, which is a special science, in this case was an extremely important investigation method. There are many examples in the world where, after speleological investigations, capital structure projects such as dams, reservoirs, tunnels, roads, railroads and the other infrastructure works were corrected or even abandoned. In East Herzegovina and Dubrovnik Littoral, the caves were the subject of interest for numerous researchers and scientists many years before the idea of utilizating water in this region appeared. Their numerous records about this remain. Only some of them will be mentioned here. Vjetrenica cave in Popovo Polje, because of its specificity, was noticed in Roman times; Gaius Plinius Secundus mentions it in the work “Naturalis Historia” in AD 77. One of the first detailed descriptions of Vjetrenica cave dates much later, in 1584 (N. Gučetić). In his writings, the Russian traveler and writer, A. Hiljferding (1873), mentions speleological research in this area being performed in 1858. Interest for speleological facilities intensified at the end of the nineteenth and the beginning of the twentieth century, particularly for Vjetrenica cave. The first drawing of Vjetrenica cave dates back to 1890. More significant investigations in this period were performed by J. Vavrović, K. Absolon, J. Cvijić, A. Lazić, S. Milojević, M. S. Radovanović and M. Kusijanović. A channel of the Ljelješnica estavelle in Dabarsko Polje was investigated by A. Lazić (1927). The largest number of speleological investigations was carried out after 1950, as part of the investigative works for the needs of construction of the Trebišnjica Hydrosystem. Investigators included R. Gašparović, O. Zubčević, I. Bušatlija, M. Malez, S. Božičević, and M. Garašić, with numerous members of their own crews. Since 1980, the speleologists of the Zelena Brda (Green Hills) society of Trebinje have been very active. Especially intensive research was carried out from 1991–1995 and from 2003–2005 (Kurtović et al., 2008). A large number of speleological facilities (about 120, predominantly shafts) were

investigated, of which only some of them are mentioned in this text. Numerous facilities in Herzegovina were investigated by the Green Hills society of Trebinje. Cave divers from Hungary dove through the siphon spring Baba and investigated the outlet channel of the Oko Spring. Pioneering speleo-diving investigations were carried out in the Doljašnica and Žira ponors in Popovo Polje (Paljetak, 1971). Cave diving siphonic research of the Ombla channel was carried out by the team of M. Krašovec in the period 1984–1994. The same team performed cave diving investigations of the siphonic channel Jama (spring of Zovidolka River) in Nevesinjsko Polje. Speleo-diving was carried out in the karst channel in search of the human fish Proteus in the temporary spring Tučevac, downstream from Trebinje and in the temporary spring Babanear the Strujići in Popovo Polje (Milanović & Milosavljević, 2003). The famous French cave diver Claude Touloumdijian has dived many times into the siphons of Buna and Bunica springs, from 1999 to 2005 (Touloumdjian, 2005). Members of his team have explored the Biograd Ponor in Nevesinjsko Polje, the Sušice channel in Dabarsko Polje and the Obodin Fatničko Polje (2000–2005) on several occasions. Despite the high density of speleological facilities (shafts and caves) in East Herzegovina and the Dubrovnik Littoral, only a small number are registered and investigated. Speleological facilities are mostly registered and partially investigated in areas that were of interest for the construction of the Trebišnjica Hydrosystem and the Ombla underground HPP project. For example, in the area between Trebišnjica and Ombla there are one to two shafts or caves recorded over 2 km2 (Fig. 3.1). During geological field mapping and production, the geological and hydrogeological maps for over 250 shafts and caves and over 600 ponors and estavelles were registered in the Trebišnjica Hydrosystem area; however, a relatively small number were investigated. A similar density of speleological facilitates is registered in the area of Stepen–Korita—Meka Gruda (Fig. 1.61) and in the wider area of Plana (Fig. 3.2). Some of the caves were detected during the excavation of hydropower tunnels, and the selection of technology of linings and repairing of defects depends directly on the results of speleological investigations. These include the karst channel in the access tunnel for HPP Dubrovnik in the hinterland of the Robinson Spring (indolomites at sea level) and numerous caverns on the routes of the Dabar—Fatnica tunnel and Fatnica—Bileća, as well as the cavern on the route of the RPP Čapljina tunnel that caused losses of tunnel lining of the power plant. Numerous caverns were discovered in the course of blanketing the bed of the Trebišnjica River with shotcrete.

3.1 Speleology Facilities Fig. 3.1 Caves and shafts registered at the area of Trebinje Forest-Ombla Spring. 1. Permanent spring Qmax > 100 m3/s, 2. Permanent spring Qmax > 10 m3/s, 3. Small spring, 4. Cave, 5. Shaft (Milanović, 2006)

Fig. 3.2 Caves and shafts at the area of Plan. 1. Cave, 2. Shaft, 3. Ponor, 4. Few close spaced ponors, 5. Small spring, 6. Bore holes (Milanović, 2006)

175

176

3 Underground Morphology and Fauna

Fig. 3.3 One of the karst channels in Trebišnjica riverbed (near Kočela village), treated on the basis of speleological investigations, 1973 (Photos Milanović)

The technical solution for each channel and cavern is based on detailed speleological recording (Fig. 3.3).

3.1.2

Miruše Area (Bileća Reservoir)

The most significant speleological facility of Miruš is the Dejanova Pećina cave (Dejan’s cave), which is the most significant source of the Trebišnjica River. The cave is described in detail in Sect. 2.1.5, Trebišnjica springs (general data), and its layout is given in Fig. 2.7. Another important speleological facility is the cave from which the Oko Spring discharges, approximately 5 km south of the Trebišnjica Spring. This cave was explored in 1961 (Gašparović, 1979). Now, the Dejan’s cave and the Oko Spring are submerged by the Bileća Reservoir.

3.1.3

Area Trebinje, Zupci and Bijela Gora

In this area, the Bravenik shaft on Grab, with a depth of 206 m, certainly is the most interesting. The general slope of the shaft is about 45 degrees (Fig. 3.4). From an elevation of 740 m, the shaft descends gradually to the north. So far, it has been explored up to an elevation of 534 m, and the channel continues by the same slope indepth. The total length of the investigated channel is 255 m. It is, for now, one of the deepest shafts in this area (Kurtovićat et al., 2008).

In the wider Trebinje area, the following shafts and caves are registered and investigated: – Pavlova cave in Mokro Polje. Research was started in 1999. A 218 m channel was investigated. – Tučevac spring. A channel of the temporary spring Tučevac near Dražin dowas investigated by speleo-diving to a length of about 250 m. The channel continues further north. It is a submerged subhorizontal channel at a depth of about 30 m, compared to the entrance level. The transverse profile of the channel has relatively large dimensions, with a width of about 10 m and 3–4 m high. The height of the channel is locally much lower. The final length of the siphon is not established. The maximum discharge of Tučevacis about 20 m3/s. Human fish (Proteus) in their natural habitat were taken by movie camera (Milanović S., 2003). – The shaft on Kučina hill in the Raptiareais 18 m deep. – Caves Matulićeva and Arenstorfova are located in the Petrina, Rapti area. – The Vilina cave in the Zupci area (Grab) was also investigated, along with Velika pećina in Dubočani and Kaporuša in the Jasen–Dubočani area. – Reconnaissance of the channel of the temporary Old Mill Spring in Poklonac was done. In the area of Bijela Gora Mountain, speleologists from Green Hills registered and investigated the following

3.1 Speleology Facilities

177

Fig. 3.4 Bravenik—shaft, Grab—Zupci, cross-section

facilities: Shaft in Medov do (depth of 19.60 m); Shaft Banjalučanka (63 m deep); Vranjež cave; Deep Shaft (depth about 150 m); Shaft on fox ridge; Mijatova Torina cave (148 m long and 40 m deep); Shaft near the houses of Grubača (60 m deep) and Mikushin shaft in the village of Orahovac (20 m deep).

3.1.4

Speleological Facilities in Popovo Polje

Numerous speleological facilities in the area of Popovo Polje have a long history of research. Among them, the most famous are certainly Vjetrenica cave near Zavala, the shaft the near Čavaš, the Meginja estavelle near Strujići, Doljašnica, Crnulja and Žira. These are only some of great number of speleological facilities in this polje. Vjetrenica cave is the most famous speleological facility in this region (Fig. 3.5). It is located on the edge of Popovo Polje, near Zavala (Fig. 1.31). A cave with a strong air current in Popova Polje was noticed by N. Gučetić (1584) from Dubrovnik. More data about this cave was presented by, Russian travel writer A. Hiljferding (1873), H. Mihajlović (1887), J. Vavrović (1893), J. Cvijić (1909–1926), Czech karstologist K. Abslon (1916 and 1932), A. Lazić (1926–1933), M. S. Radovanović (1929, doctoral

dissertation), S. Milojević (1938), M. Malez (1954–1969), R. Gašparović and numerous members of the speleological society of Bosnia and Herzegovina (1956–1970). After a longbreak, research continued in 2002 (Lučić & Sket, 2005). By law in 1952, Vjetrenica became a protected monument of nature, like a specialgeological reservation (1965). It was registered on the UNESCO list for admission to the WHL in 2004, and has been on the tentative list for world natural heritage from 2021. According to data presented by A. Hiljferding, the first caving research of Vjetrenica cave was performed in 1858. Engineers of the Sarajevo Railway Directorate investigated Vjetrenica cave in 1904. It is believed that the reason for this research was the problem of water supply for the construction camp and railway station in Zavala. Dr. Karel Absolon organized five expeditions to Vjetrenica cave. Three were in the period from 1912–1914, and two were after the First World War. The aim of these expeditions was biological research. After Absolon, a number of domestic and foreign biologists participated in investigations of the endemic fauna of Vjetrenica—S. Karaman, Lj. Kuščer, B. Sket, E. Pretnar, J. Miller, H. Stammer, J. Kratochvil and many others. According to Absolon, Trebišnjica originally flowed through Vjetrenica cave towards Ombla spring, even calls it

178

3 Underground Morphology and Fauna

Fig. 3.5 Vjetrenica cave, layoutand cross-section of the main channel (sketch Malez, 1985)

“Paleo-Ombla”. According to M. Malez, Absolon’s the unpublished article entitled “Paleo-Ombla” is located in Brno. Hypothesis of Absolon about the outflow of Popovo Polje through Vjetrenica was accepted by Cvijić, also. According to Malez (1970), significant discoveries were made in 1968, when speleologists of the South Wales Caving Club (1968), in community with domestic speleologists, blasted some places and penetrated into the continuation of the main cave channel by several hundred meters. On that occasion, a new lateral channel was discovered, with water flow that separates from the main cave channel towards the northeast, about 200 m after the Great Lake. It is in that channel that a unique paleontological finding was discovered—the fossil of the whole skeleton of a leopard, which was transferred to the State Museum in Sarajevo in 2007 (Fig. 3.6). According to oral information (from Malez, 1971), immediately nearby, the remains of a bear skeleton were found. Two important features, which make Vjetrenica different from the other caves, are the wealth of endemic fauna and a strong incessant air current through the main karst channel, by which it receives its name. Without regard to the permanent streaming air, the temperature and humidity are constant: T ≈ 11 °C and humidity 100%. Vjetrenica is the only cave in East Herzegovina which is set up for tourist visits, since 1964. There are 1250 m of the channel that are illuminated. Regarding total length of the now investigated channels of Vjetrenica, including Little Vjetrenica (lower level), there is a discrepancy between the earlier data (7503 m) and the results of newer research (about 6400 m).

Toward the goal of touristic exploitation of Vjetrenica cave, the Bosnian-Herzegovinian karst speleological society conducted a study, entitled “Measures and activities for more intensive touristic use of Vjetrenica”. The following participated in the work of this study: B. Petrović, A. Kapel, I. Bušatlija, J. Mladenović and S. Mikšić. Extracts from these studies are presented in the bulletin of the Naškrš speleological society, No. 6, 1979, Sarajevo. The most detailed description of Vjetrenica cave, including the history of research and a detailed description of endemic species in it, was given by I. Lučić, with co-author B. Sket, in the exceptionally documented monograph “Vjetrenica—a view into the soul of the earth”, published in 2003. Inclusion of Vjetrenica on the list of world heritage sites was also proposed (Lučić et al., 2005). The Zmijanac and Praljevci caves above Domaševo in Ljubomir were investigated as potential sources of archaeological findings, without positive results. Baba shaft. In the temporary spring of Baba Jama near Strujići, cave divers passa shallow siphon approximately 40 m long (2003). In this spring, by camera was also recorded Human fish (Proteus). The drypart of the channel, after the siphon, was investigated to a length of about 1100 m (oral information, Green Hills, 2005). Meginja. A drawing of the Meginja estavelle, in Popovo Polje near Strujići, at an elevation of approximately 300 m, “which throw out the water at the beginning of the flood” was presented by J. Cvijić in Geomorphology II. This was first investigated by A. Lazić in 1925. The length of the recorded channel is 285 m (Fig. 3.7). At a depth of 117 m, relative to the entrance, the Meginja channel ends with the lake. In

3.1 Speleology Facilities

179

Fig. 3.6 Vjetrenica cave on the basis of new data

natural conditions, it had the function of an estavelle. After construction of the canal through Popovo Polje, the Meginja works just in a spring regime. The same monograph displays across section of Male Jame near Čavaš (Fig. 3.8).

Ponors Downstream from Velja Međa Ponors between Velja Međa and Hutovo have been a subject of interest for speleologists and speleobiologists for a number of years. They have been investigated in detail on many occasions. In the period from 1925 to 1928, they were investigated by A. Lazić and S. Milojević; in 1969–1970 they were investigated by a crew from the geographical society BiH, from Sarajevo, led by R. Gašparović and O. Zubčević, and since 1970, on several occasions, the team the Geological Institute from Zagreb, led by S. Božičević. The cave fauna was investigated by Sket (1980). According to the data of R. Gašparović, in t 105 m of the Žira channel, 450 m of the Crnulja channel and 34 m of the Kneževac Ponor (below Trnčina) were investigated in this period. Using cave diving speleology (Paljetak, 1971), the siphon lake in the ponor Žira and one siphon in the ponor Doljašnica were investigated. Provalija and Ponikva ponors were investigated by A. Lazić and S. Milojević (1927). They investigated 450 m of the Provalija channel and 90 m of the Ponikva. In one later attempt, speleologists were not able to penetrate much deeper in these ponors. The entrance part of the Ponikva is often naturally blocked with branches and mud, so it forms an impervious plug over its opening and water accumulates over the plug. This situation lasts from one to a few months, while the suffusion process did not break the mud plug. Kaluđerov Ponor in the extreme western part of the polje was also speleologically explored. Under natural conditions, this one is rarely active because it is located high up the polje bank. Doljašnica is the most significant ponor in Popovo Polje, so it has been the subject of speleological investigation on several occasions (Fig. 3.9). The author of first drawing of the

Doljašnica channel system is S. Milojević, in 1927 (Fig. 3.10). Later, for the purposes of the HET project, Doljašnica was investigated by R. Gašparović in 1969 and S. Božičević in 1970, including diver B. Paljetak. The branched Doljašnica karst system consists of five channels, with a total length of 1750 m. All channels end with siphon lakes. The longest channel ends with the so-called northern siphon. That siphon is located at an altitude of about 90 m, which is about 138 m lower than the entrance into the ponor. The walls of the channel at water level are lined with shells (Kongeria), which indicates this siphonal ways contain water. The cave diver (B. Paljetak) went through the siphon and passed to the next cavern, which continues to the new part of the channel, above water level. It is from the cavern of the inlet of the siphon that an engineering military unit from Kotor started excavation of the gallery, in 1926, but it was quickly stopped after 9 m of excavation (Lazić, 1927). Based on the sketch of cave diver B. Paljetak, it is evident that if excavation of the gallery continued, after a few meters further the gallery would enter into the cavern at the other side of the siphon.

3.1.5

Caves Between Popovo Polje and Dubrovnik Littoral

A large number of caves and shafts were recorded in the area between Popovo Polje and the Dubrovnik area. Some of these caves were explored between 1930–1940. Systematic research of caves in the area of the village of Grepci, Slavogostići, Slivnica, Osojnik, and Mokošica and around the Ombla Spring were completed by M. Malez in 1957–1958. Fifteen caves were investigated. Basic information for some of them follows: There is a cave near the Đurkovica village of Grepciat an elevation of 520 m, and a length of 120 m. Nova (New) Đurkovica cave is 40 m from old Đurkovica on the opposite side of the sinkhole at an elevation of 518 m, and a length of about 80 m. Once upon a time, both caves

180

3 Underground Morphology and Fauna

Fig. 3.7 Meginja estavelle near Strujići, Popovo Polje (draft Cvijić, Geomorphology II, 1926, photo Milanović, 1972)

3.1 Speleology Facilities

181

Fig. 3.8 Little pits (small shafts) near Čavaš, Popovo Polje (Cvijić, 1926)

belonged to the same cave channel, whose ceiling caved in, and is a formed sinkhole that is a separate channel between the two independent caves. Poganjača cave, 500 m from the village of Grepci toward Vlaka at an elevation of 415 m, and with a total length of 150 m. At the end of the cave, the flow that sinks is registered. Mrcine cave, between Osojnik and Grebci at an altitude of 415 m consists of one channel, 312 m long. Grabovica cave, southwest of Slivnica, at an altitude of 495 m has a total length of the main cavernous channel of about 450 m.

Fig. 3.9 Doljašnica Ponor. Speleological investigations (1970)

Kali cave, west of Grepci village, is at an altitude of 485 m. The total length of the cave is about 300 m, and the channel ends with a siphon lake. Močiljska cave, south of Osojnikis at 398 m above sea level. The total length of the cave is 938 m, and the height difference between the entrance and the deepest point is 138 m. It became a tourist attraction in 1929. Vilina (Fairy) cave. The entranceto Vilina cave is located above the Ombla Spring, at an elevation of 136.36 m. The initial 65 m were explored in 1957/58. (Malez, 1970). Further passage was prevented with great tufa deposits. An intense current of air indicated that the channel continues further. Between 1986–1988, during investigations for underground HPP Ombla, tufa deposits were removed by blasting and about 3000 m of channels were speleologically investigated (M. Krašovec, between 1984–2001). The presence of two interconnected levels of karst channels was established above the groundwater level. The higher level is located between 130 and 150 m a.s.l. and is connected with the entrance into Vilina Pećina (Fig. 3.11). The lower level of the channels is located between 50 and 80 m a.s.l. From the lower part of the canal system, a steep channel is separated, which descends to an elevation of— 63 m (Fig. 3.12). This is the deepest point reached by cave divers and is located approximately 520 m behind the spring. It belongs to the third deepest level of karst channels through which siphonal flow takes place. By thermal and radar measurements along bore holes in the background of Ombla Spring, the position of siphon karst channels was established at depths of around 65 and 135 m below an elevation of zero (see Sect. 4.9 The underground damand reservoir Ombla). Speleothems in the upper channels of Vilina caves are displayed in Fig. 3.13.

182

3 Underground Morphology and Fauna

Fig. 3.10 Popovo Polje. Doljašnica Ponor, layout (Milojević, 1927)

According to D. Basara et al. (2017), of hundreds of explored speleological facilities in this area, some of the more significant caves, aside from Vilinapećina are listed below:

The cavebehind Gromačka Vlaka. After Vilina Pećinathis is the longest cave in this region—2.407 m. The elevation difference between entrance and the deepest points is 220 m.

3.1 Speleology Facilities

183

Fig. 3.11 The Vilina Pećina (Fairy cave) behind the Ombla Spring—layout (Krašovec, 1984)

Mladenovshaft, 208 m deep and Glogovajama (shaft), depth 156 m and length 428 m. Vištičinshaft, depth 144 m and length 322 m. It is known for having the biggest hibernation colony of bats in the region.

Shaft in Predolac, depth 20 m and length 56 m. It is known for having the biggest sites of cavernous shells (Congeria Kusceri). The Plješinshaft is deep 144 m and 418 m long. ShaftBezdan, Viganj, Konavosko Polje, depth 173 m. Đurovića cave is located under the Dubrovnik airport in Ćilipi (Fig. 3.14). Depth 25 m, length 156 m. It was discovered during construction works of the airport in 1960. During the extension of the airport in 2012, 11 new speleological facilities were discovered. Đurovića Cave is equipped as a tourist facility (Garašić et al., 2017). In the area of Trebimlja—Rudine–Bistrina Bay, 15 speleological facilities were investigated that are rarely longer than 30–50 m. The most significant among them are: Vranjapeć in the village of Točionik, 188 m long and 50 m deep, the Bezdanshaft (Rudine) 69 m deep (Rnjak & Hanzek, 2016).

3.1.6

Fig. 3.12 Cross-section of the deepest part of Vilinapećina (Fairy cave) channel, investigated by cave divers (Krašovec, 1993)

Speleological Facilities in Fatničko and Dabarsko poljes

In these fields are the caves of Ljelješnica, Visibaba, Sunićka, and Danojlova and the shafts of Golubinka in Dabarsko Polje, and Zvonuša and Tumorovača on the carbonate ridge between Fatničko and Dabarski Polje. In Fatničko Polje, there is temporary spring (estavelle) Obod, temporary springs Baba Jama and Pribabići, Pasmica Ponor, Velikapećina, Gnjonica and Lepirnica. Most of these investigations were carried out in 1957 (Speleological Society of Bosnia and Herzegovina) and, more recently, this area was investigated by members of the Greenhills speleological society from Trebinja. The longest cavernous system in Fatničko Poljeis Velika Pećina (Bigcave). The length of the main channel is 2365 m (Zubčević, 1959a). Big cave is, after Vjetrenica, the longest cave in East Herzegovina-2800 m including all channels. It is located on the southwestern slope, 4 m above the level of Fatničko Polje

184

3 Underground Morphology and Fauna

Fig. 3.13 Speleothems in the Vilina cave, 1989 (Photos Milanović)

(475 m above sea level), on the part that forms the Ljut carbonate ridge between these two poljes (Fig. 3.15). The cave is almost horizontal. The Zvonušacave is located approximately above the final part of the Great Cave. These two caves may represent a part of the same cavernous system. The depth of Zvonušais 112 m. Ponor Pasmica in Fatničko Polje consists of a vertical channel with a depth of 27 manda horizontal section that was investigated and recorded at a length of 47 m (Fig. 2.64). The first part of the channel lies in a south-southwest direction and the last 10 m in a westerly direction. Further passage is not possible without diving equipment. Vrelo Obod is the surface opening of the channel which is connected to the main drainage system, by which the waters from Gatačko and Cerničko Polje flow towards the Trebišnjice Springs. Investigation of Obod started in 1964 in conjunction with the Hydrosystem Trebišnjica project. The exit funnel (mouth) has an elliptical shape with a longer axis, over 50 m long, and a depth of about 40 m. It is connected to the main stream by a narrow channel (Fig. 3.16a). A relatively small part of the main karst channel was investigated upstream from the Obod opening and a significantly longer part in the downstream direction. In both directions, the explored parts of the channel ended with siphons. Further passage required utilization of cave divers. These investigations occurred during 2003 (Fig. 3.16b). The inflow channel, that is, the channel that stretches to the north, was explored by diving in 2003, at a length of approximately 150 m (Fig. 3.16b). The research was carried out by the same team of French speleologists (cave divers) who explored Buna and Bunica springs. The channel is softly

tilted towards the north so that the Obod also has the characteristics of a siphon spring. An experiment with plugging of the Obod Spring is presented in Chap. 4. During excavation of the entrance structure of the Fatnica—Bileća tunnel, it was entered through a large cavern completely filled with plastic clay, without the possibility of water flowing through it. The clay contained thousands of balls, with a diameter around 4 cm (Fig. 3.17). Most of them were approximately the same diameter, about 4 cm, and were individual, two connected (twins), or three or more connected. The balls consisted of a carbonates and fraction and the cementation was carbonate-clay, partial lithified. They were significantly different from “cave balls” in appearance (which look like polished marble balls) and with unclear genesis. Sušica in Dabarsko Polje (next to the Vrijeka Spring) was investigated by a team of French cave divers (B. Giai-Checa, August 2001). Immediately after the entrance that extends to the north, the channel turns to the west and maintains that direction along the entire length of the investigated part. The first 180 m of water in the channel is with free surface. The height of that part of the channel is over 10 m. After passing through a narrow section, with a length of approximately 15 m (approximate diameter 2 × 2 m), the channel widens and again has a height of 10 m and a length of about 100 m. At the end of this section of channel, the registered water depth is 18 m (Fig. 3.18). Research in the dry period of 2003 established that the channel of Sušica is about 2 km long (Kurtović et al., 2008). The Ljelješnica estavelle is located along the northeastern edge of Dabarsko Polje, at the beginning of the Ljut carbonate ridge. It is an estavelle but is rarely in the regime of a

3.1 Speleology Facilities

185

Fig. 3.14 Dubrovnik airport. Đurovića cave beneath airport (Draft Garašić et al., 2017, photos Milanović, 2013)

ponor. It has been investigated from 1927 (A. Lazic) to 1987. According to earlier investigations, the length of the karst channel is 396 m. According to later investigations (2003), the length of the channel was corrected to 320 m, with a lake at the end of the channel (Kurtović et al., 2008). A water gauging station is at the entrance.

3.1.7

Speleological Facilities in the Area of Bileća, Korita and Cerničko Polje

A large number of caves and pits are registered in this part of Eastern Herzegovina (Fig. 79) but only a few have been investigated. Djatlo cave is located in the hamlet of Torine, at an altitude of 1000 m, near Korita, between Bileća and Gacko. It was first mentioned in the literature by A. Lazić in 1935. It was further investigated until 2003. The cave is created in Upper Cretaceous limestone. A branched system of karst channels consists of 16 channels, with a total length of 1760 m (Fig. 3.15). The most deeply explored channel is at

a depth of 111 m. This channel has not been completely investigated (Dujaković, 2004). Near the village of Brestice, there is a 110 m deep Bezdanicashaft, at the bottom of which there is a lake of unknown depth and the 85 m deep Golubinka shaft (Dujaković & Begović, 2000). The karst channels of Vilinapećina, Ključka River Ponor and Jasovica Ponor, in Cerničko Polje, were investigated in 1961. In the Ključka river ponor (Ključki Ponor), speleologists investigated a karst channel to the siphonal lake, at a depth of 103 m. These speleological investigations were carried out with other investigative methods, with the aim of determining the reality of a formation surface man made lake in this karst polje.

3.1.8

Speleological Facilities in the Gatačko Polje Area

In the wider area of the town of Gacko, there are a small number of speleological facilities which were investigated.

186

3 Underground Morphology and Fauna

Fig. 3.15 Big cave, layout and cross-section (Left) and Đatlocave (Right). Investigation works started in 1957, as part of the investigation program for the Hydropower System of Trebišnjaca project (Zubčević, 1959b). From “Caves in the Republic ofSrpska” (Duajković, 2004)

Radoševa cave on Bjelasica Mountain was investigated to a depth of 200 m, but this is not the end of the karst channel. The shaft known as Jeftovakosa, on Bjelasica Mountain, was investigated to a depth of 127 m. Vrelskacave under Lebršnik Mountain, from which Dramešina stream discharges, consists of two channels. The lower channel, with an entrance at an elevation of 1230 m, was investigated to a length of 800 m.

3.1.9

Speleological Facilities Nevesinjsko Polje

A very small number of speleological facilities in Nevesinjsko Polje have been the subject of speleological

investigation and research. These include Jama, Jedreš, Jamnik, Oprašnica, Ponor Biograd, temporary spring Šnjetica and a few smaller facilities. The majority of mentioned facilities were investigated by S. Božičević 1984 and M. Krašovec (1986). In the valley of Drežanjskicreek, a few caves are registered in Promina conglomerates but they were not investigated. Spring cave Jama (Udbina). The channel of this spring (the source of the Zovidolka River, near Udbina) was formed in Promina conglomerates. It consists of cave and siphon parts (Fig. 3.19). The cave part consists of two channels. One is an overflow channel connected to the spring, and the other has an entrance on the slope above the source (Fig. 3.20).

3.1 Speleology Facilities

Fig. 3.16 Temporary Obod Spring (estavelle) in Fatničko Polje (after R. Gašparović). (a) 1. Open “crater” of Obod 2. Narrow channel, 10 m high and 3 m wide, connection with main channel (place of concrete plug) 3. Siphons at both ends of channel 5. Speleologically investigated part of the channel (b) Cross-section, northern channel of Obod Spring investigated by cave diver and his team (Touloumdjian, 2005)

The submerged part of the channel was explored by divers to a length of 60 m (Krašovec, 1986). The width of the channel varies from 0.6 to 7 m, and the most common height is 1–3.5 m. The first 45 m of this part of the channel has a gentle slope (average 8°). For the remaining 15 m, the channel is very steep, with a slope of 32°. The natural spring overflow threshold is approximately 20 m above the deepest Fig. 3.17 Fatnica—Bileća Tunnel, Balls formed in a cavern with plastic clay, 2005 (Photos Milanović)

187

part of the investigated siphon. From the last measured points, the channel continues to the north, under a slope of 32°. During the diving works, the water depth of the pillar in the lowest examined part of the channel was 16.5 m. In horizontal projection, the channel often changes direction. The first 30 m of the channel extend to the southeast, then change direction, to the northeast, and the last investigated part of it stretches towards the north. In order to confirm the position of the water channel, three investigative bore holes were drilled, located to enter into the karst channel. Cave of Jedreš Spring. This spring is situated on the outskirts of Nevesinje. The spring channel is formed in conglomerates of the Promina formation. It was speleologically investigated to a length of 230 m. A channel sketch was done only for the first 130 m, which consists of the covered channel and tunnel and 100 m of karst channel. More about this spring is given in Sect. 4.8.2, “Plugging of karst channel in Nevesinjsko Polje”. Cave of Jezduš Spring. The spring is located northwest of Nevesinje and was earlier used for water supply. The karst channel of this spring is formed in Promina conglomerates. The entrance into the karst channel is in the form of a pit, with a depth of about 3 m. From the pit, in a southwest direction, the gently inclined channel continues, which was speleologically explored to a length of 48 m. The channel still continues. Further research would require a diving suit, and may be even complete diving equipment. Cave of Jamnik Spring (or Jametina) is near the village of Gornja Bijenja, at the northeastern edge of the Nevesinjsko Polje, under Crvanj Mountain. The entrance to the cave is at an altitude of 952 m. The cave is made up of a subhorizontal karst channel that was investigated to a length of 147 m. In the cave is the presence of permanent underground water accumulation, which is used for water supply for the local population. Oprašnica cave is located near Humčan, close to Zlatac Ponor (northeast part of Nevesinjsko Polje). The entrance is

188

3 Underground Morphology and Fauna

Fig. 3.18 Temporary spring Sušica in Dabarsko Polje (GiaiCheca, 2002)

at an altitude of 847 m. The main channel splits into two branches. At the end of the southeast channel, there are two unexplored siphons. The water level in these siphons is at an altitude of 826 m. A total of 1050 m of channel were investigated, which is not the end of the channel. Biograd Ponor. In spite of it being a ponor with large swallowing capacity, for a long time speleologists failed to penetrate deeper into the channels because a lake with water was found not far from the entrance. It was obvious that, without cave divers, investigation was not possible. During 2004/05 French cave divers M. Gius and L. Tarazona investigated the entrance part of the karst channel (Fig. 3.21). The first part is a subvertical karst channel, about 123 m deep. After it reaches this depth, the channel changes inclination and continues in an upward direction. The long siphoned lakes along this part of the channel require

very dangerous diving. It is interesting that the first, steep part of the channel is oriented toward the southeast and, after roughly 100 m, changes direction toward the west, toward Bunica Spring. Due to extreme risks, further investigations are canceled. For more information related to Biograd Ponor, check Sect. 1.6.11 and 2.4. Temporary Spring Šnjetica is situated between Kifino village and Rilja. An attempt to investigate this spring was organized in 1986. The aim was speleological reconnaissance, diving through the steep channel of the siphon, 115 m from the entrance. Due to the possibility of sliding of the large quantities of gravel and sandback filling entrance into the siphonic part of the channel, further investigations were cancelled. Ponor Mlinica in Slato Polje was investigated in 2002 (SD Pionir, Banja Luka) The total length of the main channel, including one short branch, is 312 m.

3.1.10 Polje Gradac–Gradnica Shaft

Fig. 3.19 Jama Spring (a) layout and (b) cross-section. 1. Overflow channel towards the spring outlet, 2. Upper entrance into the main channel, 3. Water level before pumping test (Krašovec, 1986)

The opening of the Gradnica shaft is at an altitude of 86 m. Water comes out very rarely (once in a couple of years) and duration is short (1–2 days). The bottom of Gradnica is around sea level. It was investigated in 1964–1966 by the Geographical Institute from Sarajevo. The aim of this research was to determine the possibility of pumping water from Gradnice for irrigating fields. It was concluded that, in the dry period, the required amount of water cannot be obtained from this shaft (estavelle). The vertical channel is almost circular and has a diameter of 15–25 m. The short horizontal channel at the bottom is orientated in a western direction and ends after a few meters in a siphon lake.

3.2 Caves-Archaeologic Allocations

189

Fig. 3.20 Jama Spring, Udbina (a) Upper entrance into the channel developed in Promina conglomerates, Fig. 3.19, indicated by 2 (b) Channel in conglomerates from upper entrance to the cavern (Photo by Milanović, 1986)

During tracer research in the lowest part of Popovo Polje (Ponikva Žira, Lisac and Kaluđerov ponors), Gradnica was one of the important observation points. During dye tests on Ponikva and Kaluđerov ponors, in the only sample from Gradnica, a doubtful indication of dye was estimated but these results were never accepted as competent. Golubnka shaft is situated southeast of Blagaj, near the village of Vranjevići. The opening is located at an altitude of 703 m. The shaft is absolutely vertical and deep, 105 m.

3.2

Caves-Archaeologic Allocations

Despite the fact that there are a large number of caves in this region, only several of them are registered as archaeological sites. According to the available data in literature (M. Malez, V. Malez, Đ. Basler, M. Paunović), the following caves are most often mentioned: Vjetrenica has been mentioned before as the site of wellpreserved leopard remains and the remains of a cave bear, as well as bone needles from the bronze era. Green cave is located near Blagaj, above the spring of Buna. Fossil material, primarily left overs birds, was found in certain layers of Quaternary sediments. A total thickness of sediments is about 7 m. The Žuljevica Cave is located near the village of Slivnica (plateau above the Dubrovnik River). The length is only 55 m. The fragments of prehistoric ceramics were found inside and represent a potential archaeological site.

In the already mentioned Đurkovica cave near the village Grebci, on the Balkan peninsula, one of the richest sites of cavebear (Ursus spelaeus) was found (Malez, 1970). In addition to the remains of numerous generations of bears, on the lateral walls there are clear scratches from bear claws. Next to the remains of the cave hyena (Crocuta spelea), the ibex were also discovered among bears (Capraibex), as well as ceramics remains. CavePoleguša, near the Osojnik–Grepci road, has been inhabited in prehistory. Based on the artifacts found, Malez (1970) concluded that the cave was inhabited in Neolithic times, and may be even earlier, in the Mesolithic period. Močiljska cave, which was described earlier, has both paleontological and prehistoric meaning. In addition to the remains of the cave bear, numerous human skeletons and ceramics from Ironera (Hallstatt) were also discovered (Malez, 1970). Sunićka cave in Dabarsko Polje was investigated in 1976 and in 1999, at a length of 220 m. Inside, there are leftovers from the bronze era. Ceramics of early Neolithic age were registered in Jejinovača cave, above Podkom in Dabarsko Polje. In Petrova cave in Dživar (Petrovo Polje), findings dating from the Middle Ages were registered. Several archaeologically significant caves are located in the lower section of Bregava flow: Žagrica, Red, Badanj and Drenovička caves. Badanj cave is especially interesting, with an engraving in stone from the late Paleolithic era, which represents a horse.

190

3 Underground Morphology and Fauna

Fig. 3.21 Biograd Ponor. Layout and cross-section (Gius & Tarazona, 2004/05)

Archaeological research in Badanj began in 1976 (Basler, 1979). Numerous remains, including bone jewelry and snails, indicate that people lived there. According to Đ. Basler, it represents an exceptional archaeological site that goes beyond local significance. High similarity is noted between the engravings in Badanj cave and the engravings in similar settlements in Apulia and in Sicily. Archaeological remains were also recorded in Drenovačka Pećina and Žagrica, according to which both caves were inhabited by people in Roman times and in the Middle Ages. In Roman times, in the area of Stolac, there was a large settlement of Diluntum (Basler, 1979). Remains of the Roman road from the first and second centuries AD, which connected this settlement with Narona, are visible in the Bregava valley. The walls of the fortress above Stolac originate partly from the fourth century AD. The megalithic wall above the village of Ošanići in Gradina, 3 km north-west of Stolac, represents the remains of the Illyrian city Daorson, founded in the seventh or eighth century BC. This site has been known for a long time as the subject of extensive archaeological research (under international patronage). Significant archaeological artifacts dating from Early Middle Age were discovered in Dabarsko Polje.

The most famous necropolis of carved stone blocks, known as stećak, is located near Radimlja, but there are many of them in several locations along the road from Plana to Berkovići. Big, but not well-known, the necropolis is located in the western part of Dabarsko Polje, below Ljuti do. In the wide area of Gacko and Nevesinje, part of the necropolis is registered.

3.3

Caves and Shafts for Water Supply

Caves and shafts where the underground lake in the siphonal part of the karst channel is close to the entrance and accessible to people played a significant role in water supply for the surrounding population. In these caves and shafts, access to the water is usually by stairs (Fig. 4.1). For many villages, it was the only source for drinking water in a dry period of the year. In some cases, it was necessary to arrange over a hundred meter approach to the deep underground lake. There are two types of these facilities. In some of them, after depletion of the siphonal lake in a dry period, recovery of underground water level does not occur, while in other cases, the depleted water quantities slowly become restored.

3.4 Fauna

191

Fig. 3.22 Vjetrenicacave. Two examples of fauna: (a) Typhlogammarusfrosty and (b) Monolistra (Pseudomonolistra) hecegoviniensis (Sket, 2003)

Distinct examples of caves, shafts and temporary springs with water that serve as water supply for surrounding villages in a dry periodare: Šnjetica cave near Kifino village and Jamnik (G. Bijenja) in Nevesinjsko Polje; Tučevac Spring downstream from Trebinje; Oko Rasovac and Šumetin Mokro Polje (Chap. 4, Fig. 4.1). More famous caves in Popovo Polje with access to water in a dry period of the year are: Kapušanear Dračevo; Kladenac near Sedlari; Pokrivenik near Mareva Ljut; Lukavac near Zavala; and Čvaušnik near Čvaljina. For the same purpose, Perutića shaft and Reva shaft near Začula are used, as well as the spring cave Sušicain (Vučja, Montenegro) and many others.

3.4

Fauna

The area of East Herzegovina is rich in underground fauna. After the end of the nineteenth century and at the beginning of the twentieth century, numerous endemic species were discovered in the area of Popovo Polje. The majority were found in Vjetrenica cave. Numerous individuals but also organized scientific expeditions visited this area. Among the more complete descriptions of subterranean fauna of this area are the following: “Animal world of Vjetrenica” by author B. Sket in the publication “Vjetrenica, view into the soul of the earth” Lučić (2003) and “Advances in the studies of the fauna of the Balkan Peninsula: Pavičević and Perreau (2008). Samples of endemic gaovica were collected for further studies by the East West Institutes and Universities in Dubrovnik in 2007 for the international scientific and professional meeting “Endangered and endemic fish in the basins of

the rivers Neretva, Trebišnjica and Morača” and in the fields of Popovo and Dabarsko Poljes. Detailed investigations of underground habitats and fauna of the coastal belt were carried out for the underground HPP project Ombla (Geonatura, 2015). According to B. Sket (1976), Popovo Polje is one of the richest areas in Europe for fauna. The cave Vjetrenica especially represents the real of nature reserve for endemic fauna. This cave is habitat for 55 species of specialized underground (troglobionic) animals. According to new data from the same author (B. Sket, 2003 from Lučić 2005), at three nearby localities that belong to the same system (Vjetrenica, cave Bjelušica and spring Lukavac), 110 different species are registered. At Fig. 3.22 are shown two representatives of the fauna from Vjetrenica: (a) Typhlogammarusmrazeki (length up to 30 mm) which is considered a large predator and (b) Hercegovinan cavernous Monolistra (Pseudomonolistra) hecegoviniensis, length 12 mm up to 15 mm (Absolon 1916). Next to Vjetrenica, in the relatively narrow space, mass populations of some species are registered, e.g., pipe worm Marifugiacavatica in Crnulja or shell congeria (Congeriakusceri) in the Žira and Doljašnica ponors. A thick layer of Marifugia covers the walls of the deeper parts of Crnulja. During excavation of a large alluvial ponor in Popovo Polje (the Hutovo Reservoir), the karst channel with Marifugia cavatica was found, below 10 m of alluvial sediments (Fig. 3.23). It has already been mentioned that around the surface of the siphon lake, at the northern channel of Doljašnica Ponor, there are large deposits of congeria shells. According to Sket (2003), the locality of congeria is in the Žira Ponor but, by melioration of Popovo Polje, its colony

192

3 Underground Morphology and Fauna

Fig. 3.23 Marifugia cavatica (Left) and deposits of worms Marifugia cavatica in the karst channel beneath alluvial sediments in Popovo Polje (Hutovo Reservoir) (Photos and sketch Milanović)

was destroyed. Shells of congeria are found in Vjetrenica’s ultimate southeastern site. Certainly, the most attractive inhabitant of the karst underground is Proteusanguinus Laurenti, the so-called “humanfish” (1768). Human fish is the only vertebrate in Europe that has completely adapted to life in underground waters (Čučković, 1978). A long time ago, the presence of human fish was registered in 37 localities in the area of Popovo Polje and the wider Trebinje area (Fig. 3.24). Natural food for human fish is freshwater shrimps Triglocaris and Nipharagus and also individual larvae of some species of underground fauna. Among the more significant localities with human fish, Čučković lists the following: Lušac and Studenac springs, Oko Rasovac, Tučevac and seven more localities in Trebinje

itself. Of the 28 localities in Popovo Polje, the most important are Pokrivenik (Mareva Ljut) near Zavala, the estavelles of Meginja and Baba near Strujići, the Vjetrenica cave, the estavelles of Jamina and Jaretica, below Dračevo, and others. Divers in the area of Popovo Polje recorded a human fish for the first time, in its natural environment in the submerged channel of the temporary spring Tučevac and estavelle BabaStrujići area (Milanović & Milosvljavić, 2003). It was found that the human fish also inhabits the karst channels upstream of the Gorica Dam (estavelle Gorica). Investigative cave diving in the channel of Ombla Spring obtained a specimen of a human fish, approx. 4 cm long (verbal information by Krašovec, 1986). After that, despite long-term observations and numerous research in the framework of the underground HPP Ombla project, the human fish

Fig. 3.24 (a) Photo of the Proteus (“Human fish”) taken in the submerged channel of Tučevac Spring near Trebinje (Photo S. Milanović) (b) Proteus in Lower Vjetrenica cave. Photo by R. Ozimec

References

Fig. 3.25 Gaovica fish from Popovo Polje (Paraphoxinus Ghetaldi)

was not observed. It was most likely this individual was brought by water from the hinterland (Popovo Polje), because the channels of the Ombla Spring are not habitat for this species. Three of seven endemic species of gaovica fish live in the estavelles and ponors of East Herzegovina. These are: Gatačka gaovica (Paraphoxinus methohiensis), Trebinjska gaovica (Paraphoxinus pstrossi) and gaovica from Popovo Polje (Paraphoxinus ghetaldi). It can grow up to 13 to 15 cm. This endemic species spends the summer in the siphonic part of karst channels (underground). When estavelles work in the regime of springs, gaovica comes into surface streams and lakes and lives there until the water recedes. Then, through the estavelles, which work as ponors, they pull back into the underground where they wait in siphonic lakes for the next rainy season. Gaovica had a significant role in nutrition for the salmonid species and, at the same time, played a role in the nutrition of the population of Popovo Polje (Čučković, 1978). They were caught in nets and baskets at the openings of the estavelle during water withdrawal and, by a drying process, were prepared for food in the winter period (Fig. 3.25). Gaovica is an endangered species. Estavelles of Mokro Polje, are wealth with gaovica fish. Important habitats of this kind of fish are estavelles: Uspotnica, Vučonica, Obarak, Prtenjača, Oko Rasovaci Djurovdo. Gatačka gaovica inhabits the waters of Gračanica, Mušnica, Zalomka (insprings near Fojnica) and flood waters of Lukavačko and Cerničko Polje. The presence of gaovica is registered in Pasmica Ponor in Fatničko Polje. The presence of gaoviceis registered in Vrijeka flow in Dabarsko Polje. Next to the gaovice stream of Vrijeka is a habitat for triton (scaly amphibians), otters and brook trout. Trebinjska gaovica used to be numerous in Čepelica and in the area of Miruše, but its number declined sharply after 1900 and it almost disappeared, probably due to importation of the predator rainbow trout. Gaovica also inhabits underground water in Ljubomirsko Polje. Gaovica from Popovo Polje massively inhabited estavelles between Dračevo and Strujići. With termination of high floods, due to construction of the Hydrosystem Trebišnjica, survival of this species is endangered. Among the most common residents in the unflooded part of underground karst are bats. They inhabit a number of

193

caves in this region. For the PP Ombla project, detailed investigations of numerous caves were carried out, especially of Vilina cave, which is part of the Omble karst system. It was established that this cave held seven different species of bats, of which there are significant colonies of: Rhinolophus ferrumequinum, Rhinolophus euryale, Myotis blythii, Miniopterus schreibersii, Myotis emarginatus (Geonatura, 2015). For the needs of the Trebišnjica Hydrosystem project, with the aim of determining the underground connection in East Herzegovina, a hydrobiological method was applied. This method is based on the endemic organisms which inhabit submerged karst channels. Diversity of life conditions results in versatile differentiation of organisms, so that certain localities are inhabited by fauna specific to that locality. This method was applied in the Trebišnjica, Zalomka and Bregava catchments in 1956. Samples for analysis were taken from 39 points. Conclusions about underground connections were made mainly on the basis of large numbers of subterranean amphipods and mollusks. Many of these conclusions are confirmed by tracer tests. It is interesting to note that, according to these works, the biological underground connection between Dabarsko and Fatničko Polje has not been determined, that is, the underground waters of Dabarsko and Fatničko poljes are not inhabited by the same organisms (Georgijevski et al., 1966). Hydrological and hydrogeological field investigations (1973) and more recent analyses indicate that there are clear indications of the hydrogeological connection between Fatničko and Dabarsko Poljes but it is a rare and short-lived phenomenon. This connection is not realized directly through the limestone ridge Ljut, which divides these poljes. Connections occurred through the rock mass of the rim of the southern poljes, during extreme levels of underground water. After tunnel excavation between these poljes, direct communication of organisms between them was enabled. Due to this circumstance, there is a question about possible disturbance of the natural balance of organisms and what kind of consequences are expected.

References Absolon, K. (1916). Z vyskmnych cest po Krasech Balkana. Zlata Praha, 4, Reč. 33. Prag. Absolon, K. (1932). Die unterirdische Flüsse Ombla und Buna. Vortrag am 23.II 1932. Roterdam. Tijdoschr.v.h.Kon.Ned.Handrijksk. Genootsch. Leiden, 2 Reihe, 49, 4.Roterdam. Basara, D., Rnjak, G., & Ozimec, R. (2017). Important speleological objects of Dubrovnik-Neretrva comunity. Meeting of Croatian speleologists. In Croatian. Proceedings, Summary. Ćilipi 2017, Croatia. In Cratian. Basler, Đ. (1979). Archeological caves in Bregava valley. “Naš krš”, Bulletin of Speleological Society Bosnia and Herzegovina karst, No. 5, Sarajevo. In Serbian.

194 Božičević, S. (1984). Morphology of the spring caves with the conglomerate of the Velež Mountain. Naš Krš, Bulletin of Speleological Society of Bosnia and Herzegovina karst, No. 16/17. Sarajevo. In Croatian. Cvijić, J. (1926). Geomorphology II. Beograd. In Serbian. Čučković, S. (1978). Question of possibility to survive well known endem human fish in area of Hydrosystem Trebišnjica. Proceedings: Conference on influence of man made reservoirs on environment. In Serbian. Yugoslav Commiittee of Lage dams (JKVB). JKVB and HET. Trebinje, Herzegovina. In Serbian. Garašić, M., Krpina, I., Garašić, D., & Gospodinović, T. (2017). Investigation of less known speleological forms at Dubrovnik area during last 20 years. Conference of Croatian speleologists. In Croatian, Proceeding of summaries “Ćilipi 2017”. Croatia. In Croatian. Geonatura. (2015). Study – The main evaluation of acceptance of PP Ombla for ecological net. Zagreb. In Croatian. Georgijevski, M., Gligić, M., Karaman, S., & Petkovski, T. (1966). Hydrobiological study of underground water connections in catchment area of Trebišnjica River. Elektroprojekt. In Serbian. Dujaković, G. (2004). Caves and shafts of Republic of Serpska. Institute for text-books and and teaching facilities. East Sarajevo. In Serbian. Dujaković, G., & Begović, P. (2000). Cave Đatlo. 4. conference about karst protection. In Serbian, Despotovac. Academic speleologicalpinistic club, Beograd. In Serbian. Gašparović, R. (1979). The contribute of speleologists of Bosnia and Herzegovina at construction of some hydro power structures and scientific investigations in karst. Naš krš, Bulletin of Speleological Society Bosansko-hercegovaški krš. No. 7. Sarajevo. Giai-Checa, B. (2002). Vrijeka, Dabarsko Polje. In: Compte rendu de L'expedition nationalle 2001 de plongee souterraine en Bosnia and Hercegovina. By C. Toulomdjian at all. Naš Krš XXII, 35. 2002, Sarajevo. Gučetić, N. V. (Gozze, Nicolo Vito). (1584). Sopra le Metheore d’Aristotile, Venecija. Hiljferding, A. (1873). Bosnia, Herzegovina and Old Serbia. (In Russian) St. Petersburg. Krašovec, M. (1984). Speleo-diving investigations of Dubrovnik River Spring – Ombla. Institute for Geology. In Slovenian. Krašovec, M. (1986). Report of speleo-diving investigations in Spring Jama, Udbina, Nevesinjsko Polje. Not published. Krašovec, M. (1993). Ombla Spring. Investigation of submerged karst channels. Report. Not published. Ljubljana. In Slovenian. Kurtović, D., Perreau, M., Queinnec, E., & Pavićević, D. (2008). Report of the international speleological and biospeleological expeditions in Herzegovina and Montenegro (2003–2005). In D. Pavićević & M. Perreau (Eds.), Advances in the studies of the fauna of the Balkan Peninsula. Monograph No. 22. Institute for nature conservation of Serbia, Beograd. Lazić, A. (1927). Ponors and estavelles in Popvo Polje. Herald of Serbian Geografic Society, 13. Belgarde. In Serbian. Lučić, I., Bakšić, D., Mulaomerović, J., & Ozimec, R. (2005). Recent research into Vjetrenica cave (Bosnia-Herzegovina) and the current

3 Underground Morphology and Fauna view of the cave regarding its candidature for the World Heritage List. 14th international speleological congress. Lučić, I. (2019). Presvlačenje krša. Hystory of knowledge of Dinaric karst – Case study Popovo Polje. In Croatian. Synopsis, Zagreb – Sarajevo. In Croatian. Malez, M. (1970). Speleological objects between Popovo Polje and Dubrovnik. Report, Zagreb. In Croatian. Malez, M. (1985). Paleobiological relations in Vjetrenica cave in Popovo Polje, Herzegovina. Naš krš XI, 1-19, Sarajevo, In Croatian, pp. 121–132. Mihajlović, N. (1887). Vjetrenica Cave in Zavala. Herald of National Museum, Bosnia and Hezegovina, 1.Sarajevo. Milanović, P. (2006). Karst of Eastern Herzegovina and Dubronik Littoral (1st ed.). ASOS. Milanović, S. (2003). Scientific movie “Forgotten species. Milanović, S., & Milosavljević, A. (2003). Diving in Tučevac Spring and Baba Estavelle, Popovo Polje. Report. Not published. Milojević, S. (1927). A few caves and shafts in Popovo Polje. Buletin, Serbian Geograpical Society, No 13. Belgrade. In Serbian. Milojević, S. (1938). Some questions about hydrographic properties of cave Vjetrenica (Popovo polje) - karst problems. Separate edition of S.S.N., 123, Beograd. Paljetak, B. (1971). Diving in Doljšnica Ponor, Popovo Polje. Report. Not published. Pavićević, D., & Perreau, M. (2008). Advances in the studies of the fauna of the Balkan Peninsula. Papers dedicated to the memory of Guido Nonveiller. In Pavićević & Perreau (Eds.), Institute for nature conservation of Serbia (p. 564). Radovanović, M. S. (1929). Vjetrenica Cave in Herzegovina. Morphological-hydrographic Study. Herald of Serbian Royal Academy, 68. Beograd. Rnjak, G., & Hanžek, N. (2016). Speleological investigations at Dubrovnik area. Subterranea Croatica. Zagreb. In Croatian. Sket, B. (1976). Wealth and endangering of karstic fauna in the area of Popovo Polje. Yugoslav speleological Congress. Herceg Novi, Montenegro. Sket, B. (1980). Richnes of endangered cave fauna in area Popovo Polje. 7th Yugoslav speleological congress, Herceg Novi 1976. Titograd. pp. 403–409. Sket, B. (2003). Animal world of Vjetrenica. In Lučić I. Vjetrenica, wiev in soul of earth. Zagreb – Ravno. In Croatian. Touloumdjian, C. (2005). The Springs of Montenegro and Dinaric Karst. Proceedings of the International Conference Water Resources and Environmental Problems in Karst - Cvijić 2005, National Committee if IAH of Serbia and Montenegro, Belgrade. Vavrović, J. (1893). Some information about Vjetrenica Cave. Herald of National Museum, Bosnia and Herzegovina 5. Sarajevo. Zubčević, O. (1959a). Speleological investigations in Big Cave (Velika pećina) and shaft Zvonuša. “Geographical Overview”, Vol3, Sarajevo. pp. 19–33. Zubčević, O. (1959b). Big cave, Fatničko Polje. Investigation works. Report. From Caves in the Republic of Srpska (Dujaković, 2004). Eastern Sarajevo.

4

Water Resources Projects

Grančarevo Dam

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. Milanović, Karst of East Herzegovina and Dubrovnik Littoral, Cave and Karst Systems of the World, https://doi.org/10.1007/978-3-031-28120-4_4

195

196

4.1

4 Water Resources Projects

Introduction

The nature of karst resulted in a centuries-old struggle for survival in the area of East Herzegovina. Due to limited natural resources, the population density in the municipalities of this area ranged between 15–29 inhabitants per square kilometer, with a decreasing trend (in the period 1961–1981 from 7% to 27%). The only larger agricultural areas are in the karst poljes and in the area of Dubrava which, in relation to the total area, is about 7%. The only real natural resource is precipitation. However, due to the nature of karst and uneven distribution of precipitation during the year, the winter period results in flooding of karst poljes and summer period in shortage of water and drought. Shifting the flood and drought is described with the short phrase: “lightning—flooding— shining—burning”. Underground runoff is dominant. Surface flows are rare and, in a dry period, they dry up. Even where the average annual precipitation is greater than 3000 mm, in the dry season there is no water for elementary vital needs. To provide the necessary amount of water for the dry period, cisterns were built and filled with rain water during periods of precipitation. One possibility for drinking water in periods of drought is siphonal lakes in the karst channels of some temporary springs. Examples of temporary springs that have access to water in dry periods are Oko Rasovac and Šumet in Mokro Polje (Figs. 4.1). Among the first melioration measures are ponds for accumulating water, construction of stone dams for the needs of mills, construction of mills on sinkholes, and construction of simple walls to keep back water, with irrigation buckets. In order to ensure at least the minimum amount of water for the dry period, simple small ponds were built. The most convenient ground for construction is grussified dolomite, in

which it is possible to achieve satisfactory watertightness. A smaller number of these ponds are still in operation (Fig. 4.2). One of the oldest hydrotechnical facilities in this region is the water intake in Konavsko Polje, with a water transport system that dates back to the Roman period and served as water supply of for the town of Cavtat (Epidaurus). The most famous facility is surely the system for the water supply of Dubrovnik—(Onofrio’s Fountain). In the period 1436–37, a canal was built from the Šumet spring to the fountain in Dubrovnik, with a length of 11,700 m and a flow capacity up to 70 l/s. One of the characteristics of Popovo Polje is the numerous mills built over ponors along the Trebišnjica riverbed. They are mentioned in ancient documents from the fifteenth century. Mills represent simplified but complete hydrotechnical facilities, which use water energy to move millstones (Fig. 4.3). Along with for Popovo Polje, mills were built in Fatničko Polje (Obod), Ljubomirsko Polje (mill on the Šanici), in pre-ponor zones at Cerničko, Lukavačko and Slato Polje, and on the Buna River. Between Trebinje and Velja Međa, there were dozens of mills. During construction of RPP Čapljina (1970–1971) and concreting of the Trebišnjica riverbed by shotcrete, most of the mills was destroyed. There are only two mills near Dobroman and one near Poljica preserved as monumental facilities of an earlier epoch. In order to obtain energy to start the mills at Obod Spring in Fatničko Polje, a 6-m high stone dam was built (Fig. 4.4). The mills were operational only when water flowed out from Obod but was not yet totally submerged, which was the case during high flood levels. Changing of water regimes is presented in numerous legends that include closing the ponors with ox hides, diverting streams, etc. The most common closure method uses

Fig. 4.1 (a) Oko Rasovac Spring, 2005. Stone stairs are constructed down to the water level (siphon) for water supply in a dry period of the year (Photo Milanović). (b) and (c) Stairs to the water level in temporary spring Šumet, 2021. (Photo Imširović)

4.1 Introduction

197

Fig. 4.2 Ancient ponds in East Herzegovina. Left—pond in the village of Boljuni, near Stolac; Right—Roko’s pond at Klobuk, 2015 (Photo Milanović)

beams, which are covered with block stones and a layer of soil (Fig. 4.5). Such constructions rarely last more than one flood. Ponors are often walled with drywall, in order to enable unhindered drainage water, that is, reduce the duration of floods, simultaneously preventing erosion, and taking away arable land (Fig. 4.6). In order to reduce the time of flooding, engineering works were also attempted, with some ponors to be included earlier in the drainage, as well as to increase permeable capacity of individual channels by blasting. In 1925, a canal was dug, with a length of 732 m, from the Trebišnjica riverbed to the Doljašnica Ponor. The next year (1926), a military engineering unit was hired that dug a tunnel in the Doljašnica channel at a depth of 116 m and connected the channel between the two parts of the siphon (Lazić, 1927). After a couple of meters of excavation, it was stopped and the idea was abandoned. Ideas about a more modern approach to using the water potential of this region first appeared during the AustroHungarian occupation of Bosnia and Herzegovina. Special attention was paid to Trebišnjica, whose hydrological characteristics were analyzed as early as 1887 and, in 1907, projects were proposed for the improvement of Popovo Polje. In a book about water potential of karst areas in the south of the Austro-Hungarian monarchy (1911), Engineer Th. Schenkel proposed hydropower utilization of Trebišnjica waters, with two power plants (Kovačina & Miljković, 2004). According to the first proposal, water would be taken from the water intake in Trebinje and transported by canal for 14 km, through the Trebinje Forest and a 3.5 km tunnel towards the Dubrovnik River. On the descent to sea level, it would be used at the power plant near the Ombla Spring. According to the second variant, the water would be led from Popovo Polje through a canal 8.2 km long and a tunnel 4.5 km long towards Slano at sea coast, where the

power plant would be. Apart from these, there was also a proposed tunnel from Popovo Polje near Turkovići to transport water above Bistrine Bay and, on the decline to sea level, to be used for production of electric energy. A more significant reclamation project was utilized for irrigation in Gatačko Polje, with construction of the Klinje Dam (1896). Figure 4.7 shows the melioration system of part of the Gatačko Polje, with the key structure—the Klinje Dam. The system for drainage and irrigation of 575 hectares consisted of a network of main canals with a length of 29.1 km, secondary channels with a length of 29.0 km and six water gates (Ballif, 1896). In 1888, observations of water regimes were started for the purpose of reclamation of the area of Hutovo Blato, and the first project proposals were done in 1910. Investigative works (exploratory drilling) started in 1929. In the period 1950–1965, there were numerous investigative works (Šarin et al., 1965), and the project was only partially realized (so-called Višićka cassette). In the period 1899–1907, the first investigations for water supply in the region were carried out. On the base of design, documentation of the first water supply system for Trebinje, with water intake in Oko Spring was completed. At the same time, Jedreš Spring was tapped in Nevesinjsko Polje. In the period 1938–1939, upstream of Grančarevo, the Parež hydroelectric power plant was built. This energy served, first of all, as pumping equipment for the water supply of Trebinje and Bileće. Presently this area is submerged by Bileća Reservoir. After the Second World War, a tunnel was excavated for the drainage of Konavosko Polje. In 1962, the Alagovac Dam was built in Nevesinjsko Polje to supply water for the town of Nevesinje. However, all of the mentioned interventions were partial solutions of local significance. Extensive analyses have shown that the unfavorable natural water regime can only

198

4 Water Resources Projects

Fig. 4.3 Above—Ancient mill near Dobromani, Popovo Polje (1970). Below—Crosssection of typical ancient mill in Popovo Polje 1. Cylindrical stone wall 2. Water gate 3. Millstone 4. Wooden turbines 5. Water inlet 6. Karstified limestone 7. Karst channel between ponor and turbines 8. Riverbed 9. River water level. (Photo Milanović)

be changed by construction of a regional water management system, which will regulate the majority of water potential in East Herzegovina. With partial and local solutions, optimal use of water at a regional scale is not possible. This assumption was the basis for creating the Hydrosystem of Trebišnjica.

4.2

Multipurpose Hydrosystem Trebišnjica (HET): Conception

Control and management of water is the only solution for the needs of the population and the development of the region. In all cases of drastic human impact on nature, it is necessary to

find the right balance between the needs for development and prosperity and preservation of important natural characteristics of the region. Due to the nature of karst, it is in a very delicate condition. This was permanently in the mind of designers and decision makers of “Multipurpose Hydrosystem of Trebišnjica” (HET). To change water regime, which is unfavourable in natural conditions, is possible only by construction dams and reservoirs in selected locations and transportation of accumulated water to the areas where it will be optimally used. The largest part of the waters of East Herzegovina flows in the wet period, in the form of flood waves, when almost all karst poljes flood. Dry periods are long, with much expressed

4.2 Multipurpose Hydrosystem Trebišnjica (HET): Conception

199

Fig. 4.4 Fatničko Polje. Ancient dam in front of Obod Spring. Left—downstream view. Right—upstream view, 1995 (Photos by Milanović)

Fig. 4.5 Ponor protection 1. Karst channel 2. Timber construction with t loading 3. Alluvial sediments 4. Soil material 5. Walled-in structure

water deficit, and because of long-term drought, the possibility for agricultural activities is extremely limited. In the time of the Austro-Hungarian occupation and also in the period between the two world wars, a number of analyses were done, with the goal of determining how much to mitigate this “defect” of nature. The first concept, which is the basis of the current system, was created in 1953in a water management basic document, compiled by the Institution for Water Management in Sarajevo. That conception was reworked in 1954, modified and adopted in 1956. Prof. S. Mikulec had a key role in the formation and realization of this concept. It is based on earlier knowledge about geology and hydrology of this region and on the first dedicated geological documentation (Sikošek, 1954 and Mladenović, 1966). Intense research began in 1954, the conceptual project was finished in 1956, and implementation of the first phase began in 1959, with the foundation of a company called Hydropower Plants on Trebišnjica in the town of Trebinje.

In the first phase, the system was based on large water potential and the cascading position of the karst poljes, whose geographical position enables energy utilization of East Herzegovina water, from an altitude of 900 m to sea level. Investigations regarding future facilities began in 1961 (K. Torbarov, Energoinvest, Sarajevo). During construction, the first phase was done using the basic water management document, “Karst Poljes of East Herzegovina”. This concept included construction of large reservoirs, Bileća (V = 1.27 × 109 m3) and Nevesinje (V = 1.55 × 106 m3), and smaller reservoirs in Cerničko and Slato Poljes. In addition to HPP Trebinje I and PP Dubrovnik, the construction of the following was planned: HPP Cernica, HPP Fatnica, HPP Dabar and HPP Bileća. Research works for HPP Cernica were carried out from 1963–1965, and the preliminary design was done in 1967. The investigative works showed that the hydrogeological characteristics of Cerničko Polje are not favorable for reservoir formation, so this idea was abandoned.

200

4 Water Resources Projects

Fig. 4.6 Walled-in ponor in Fatničko Polje to prevent plugging. (Milanović, 1981)

After completion of the Grančarevo and Gorica dams, respectively PP Dubrovnik and HPP Trebinje I, the original concept was supplemented with a canal through Popovo Polje and the new power plant—RPP Čapljina. Because of huge problems with watertightness (extremely karstified Žiljevo limestone ridge), the idea for a large reservoir in Nevesinjsko Polje was abandoned. On the foundations created in 1956 and 1967, the Hydrosystem Trebišnjica played a dominant energy role in the beginning. It was later transformed for multi-purpose use and protection of water and environment in the area of East Herzegovina and the Dubrovnik Littoral. The essence of this concept consists of accumulating water during periods of intense rainfall for multipurpose use throughout the year. The system represents a unique technological unit and can provide optimal effects for development of the entire region. During construction, the concept evolved in the direction of even contribution development for the whole of East Herzegovina, along with equal protection for water resources and environment in every part of this region. In order to achieve that goal, it was necessary for part of the water

flowing uncontrollably underground towards the seacoast in the Neretva valley stay on the surface for as long as possible and accumulate in selected locations. In this way, flooding of agricultural areas was significantly shortened. Because of this, agricultural production was considerably improved, and water was used for electric energy production, at a great elevation difference. The affected part of the water is from the highest karst poljes to sea level, and it takes a route that covers the largest part of East Herzegovina—the so-called “S” route (Fig. 4.8). Part of the Hydrosystem Trebišnjica, which captures the northwestern part of East Herzegovina and in which the Nevesinjsko and Dabarsko poljes dominate, is known as Upper Horizons (Fig. 4.10). The first conception of using water of Upper Horizons was adopted in 1967. Through detailed investigations and analyses, it was established that the water of Upper Horizons could be kept on the surface longer and used more efficiently compared to the original idea. Therefore, a new concept was proposed (1977), with a reservoir in the Zalomka valley, a regulatory pool in Nevesinjsko Polje and power plants Nevesinje, Dabar

4.2 Multipurpose Hydrosystem Trebišnjica (HET): Conception

201

Fig. 4.7 Gatačko Polje. General reclamation plan of Gatačko Polje after Klinje Dam construction. Taken from “Reclamation of Gatačko Polje”, Vienna, 1896.

and Bileća. This conception implies conveyance of part of the water from the Buna, Bunica and Bregava catchments into the Trebišnjica catchment, and itsuse in the already operational facilities of the first phase of the system. Water management consent for starting the construction facilities of Upper Horizons was obtained in 1986. An abbreviated version of the project was translated into English and submitted to the International Bank for Reconstruction and Development in Washington. Revised documentation was done in 1990 (Energoinvest, Sarajevo). From 2001, regarding actualization and updating of project documentation for Upper Horizons (HPP Dabar and HPP Nevesinje), including detailed geological terrain reconnaissance from Gatačko to Dabarsko Polje, EnergoprojektHydroengineering, Belgrade was engaged and, since 2011, JV Jaroslav Černi Belgrade & Stucky, Lausanne. Conceptual solutions and multi-purpose use of the waters of Upper Horizons were created by the Institute for Water Management, Bijeljina (2008).

According to the final concept, the multipurpose system of the Hydroelectric Power Plant on Trebišnjica consists of the following: seven hydroelectric power plants with six reservoirs; six dams; six tunnels,, with a total length of 59.7 km; several access tunnels; 62.5 km of concrete canal through Popovo Polje; a canal through Dabarsko (6750 m) and Fatničko Poljes (2770 m); and, a tunnel-canal (or pipeline) system, towards Dubrava (Figs. 4.9 and 4.10). The key obstacle in the realization of the Trebišnjica Hydrosystem was the nature of the karst. Formation of watertight reservoirs, especially a huge one like the Bileća Reservoir, in an area that represents a world rarity when it comes to karst, is considered to be impossibly by a number of scientists and engineers. The first structure, the Gorica Dam, and the first phase of HPP Dubrovnik were completed in 1965. Filling of the Bileća Reservoir started on 11 November 1967, and the HPP Trebinje was commissioned and released on March 25, 1968.

202

4 Water Resources Projects

Fig. 4.8 East Herzegovina and Dubrovnik Littoral 1. Reservoir 2. Karst polje 3. Alluvial sediments and wetland area 4. Karst spring 5. Ponor 6. Submarine spring 7. Regional fault 8. Underground

connection 9. Permanent surface flow 10. Temporary surface flow 11. States border 12. Entity border 13. Main underground flow direction (Milanović, 2010)

At the end of 1968, a decision was made to replace the second phase of the HPP Dubrovnik with RPP Čapljina, with

key facilities such as: watertight canal through Popovo Polje, along the route of the Trebišnjica bed (65 km); upper

4.2 Multipurpose Hydrosystem Trebišnjica (HET): Conception

203

Fig. 4.9 General schemes of multipurpose Hydrosystem Trebišnjica—layout. 1. Altitude 2. Temporary flow 3. Permanent flow 4. Tunnel route 5. Dam site. 6. Power plant (operational) 7. Power plant (designed) (Milanović et al., 2012)

regulatory pool Hutovo; head race tunnel length of 8 km; pump hydroelectric power plant on the rim of Svitava depression and the lower regulatory pool Svitava. RPP Čapljina has been operating since 1979. The power plant Trebinje II, which become operational in 1981, is used to control flow on the Gorica Dam, toward RPP Čapljina. The power plant guarantees ecological flow through the urban area of Trebinje, next to the Gorica Dam. Basic characteristics of designed, operational hydroelectric power plants are presented in Table 4.1.

Table 4.1 The main parameters of Hydrosystem Trebišnjica Hydropower plant HPP Trebinje I HPP Trebinje II HPP Dubrovnik RPP Ĉapljina HPP Nevesinje HPP Dabar HPP Bileća

Volume Accumulations (GWh) (hm3) 1280 110 15.9 6 – – 5.2 3 ? 100.6 ? 270.6 + 228 – 117

Installed power (MW) 180 8 210 420 61 160 30

204

4 Water Resources Projects

Fig. 4.10 Hydrosystem Trebišnjica, longitudinal cross-section

In addition to the mentioned power plants, an elaborated variant of Trebišnjica water utility at HPP Boka in Boka Kotorska Bay was built in 1992, with installed capacity of 252 MW and production of 1330 GWh per year. A brief description follows of selected hydrogeological and geotechnical problems that were solved during the implementation of the system. This also includes some facilities which are not a formal part of Hydrosystem Trebišnjica but whose waters belong to this catchment area (Klinje, Vrba and mine of Thermal Power Plant Gacko) or are located in the wider area of the analyzed region (drainage tunnel in Konavosko Polje and project of underground HPP Ombla).

4.3

Reorganization the River Networks in Gatačko Polje

The presence of coal in the Neogene sediments of Gatačko Polje has been known for a long time, and the possibility of its use for thermal energy production was considered in 1970. Coal was earlier excavated in the small open Vrbica mine, between Gacko and Avtovac. Assessment of reserves and quality of coal for future thermal power plants started in 1971. According to the investigation program by the Geological Institute in Sarajevo, 1970–71, exploratory drilling and geophysical investigations started in May 1971. The open pit coal mine for TPP Gacko (300 MW) is extremely sensitive to the extreme hydrological events that are characteristic for the Gatačko Polje catchment area. The Gatačko Polje catchment, that is, the Mušnica River

catchment, borders part of the regional Adriatic Sea catchment, with Black Sea catchment area. The Mušnica catchment, except for the small Sušica catchment, is the only catchment area in East Herzegovina with dominant surface outflow that terminates in the ponor zone in Malo Gatačko Polje. A more detailed explanation of geological, hydrogeological and hydrological characteristics of the polje, as well as the Mušnica catchment, is presented in Sect. 1.6.10 and 2.1.4. With the beginning of open mine operation in 1978, the regime of surface and underground waters in the Mušnica catchment was significantly disturbed. To ensure undisturbed coal exploitation, complex geotechnical and hydrotechnical works were undertaken. For this reason, in the period 1975–1978, the riverbed of the Mušnica River in the area of the mine and Gojkovića creek was relocated (Fig. 4.11). Further interventions in the displacement and regulation of these flows were carried out during the period 1981–1983. For protection against underground water along part of the northern edge of the polje, a grout curtain with a length of 1330 m was made. Work on the curtain began in 1981. Thermal power plant becomes operational in 1983. In this area, the amount and intensity of precipitation are often extremely high, and there are problems with defense against inflow into the mine. This covered an ever-increasing area and were a frequent occurrence, so the measures taken were not always sufficient. So, in 2013, extreme rains in the period January–March (1034 mm) caused formation landslides (March 9, 2013) and flooding in the Gračanica open mine, Field B. This is why there was an urgent relocation of the

4.4 Dams and Reservoirs

205

Fig. 4.11 Gatačko Polje. Natural and displaced riverbeds (Dašić & Vasić, 2020)

2030 m long Gojkovića creek. It was placed along the western edge of Field B and parts of the Mušnica riverbed along the southern edge of Field B of the Gračanica open mine, 1560 m in length. In order to minimize the risk of open mine flooding directly from the Mušnica riverbed in periods of extreme precipitation, the riverbed was displaced in Gatačko Polje, along the Gacko—Kula road, by cutting through the limestone ridge that separates the Large and Small Gatačko Polje. Cross cutting was done on location (Figs. 4.11 and 4.12). Further, through the Malo Gatačko Polje, the displaced flow of the Mušnica is connected by a canal to the Mušnica riverbed, i.e., with the ponor zone along the south-west edge of Malo Gatačko Polje, through which the waters of the Mušnica catchment flow towards the springs of the Trebišnjica River. The total length of the displaced flow (canal) of Mušnica is 5663 m. Because of this structure, the water of the Mušnica does not flow through the Srđevići

gorge. Through the profile Srđevići, only the water of the Gračanica River and Gojkovića creek flow now.

4.4

Dams and Reservoirs

4.4.1

Dam Klinje

Attempts to improve a very unfavorable natural water regime (replacing floods and droughts) and at least extend the vegetative period in karst poljes began in the last decades of the nineteenth century. The chapters on Fatničko and Dabarsko poljes mention the efforts of Austrian engineers to maintain ponors, in order to shorten the duration of floods, and the formation of the first hydrological water gauging stations. The largest reclamation projects of that time date from the period the Gatačko Polje was realized. The works were started in 1888 and finished in 1896. Works were managed

206

4 Water Resources Projects

Fig. 4.12 Gatačko Polje (a) Displaced flow of Mušnica River (canal) inside Malo (Small) Gatačko Polje (b) Displaced Mušnica canal cut into the carbonate ridge at the Senokos area (c) Malo (Small) Gatačko Polje, panoramic view, 2016 (Photos Milanović)

by Philip Ballif, construction advisor of the AustroHungarian government for Bosnia and Herzegovina. The goals of the system are listed below: – drainage-soaked parts of land to be cultivated – irrigation in springtime and summer – regulation of the flow of high waters but without the intention to prevent autumn and spring floods – acceleration of the transition from swamp vegetation to vegetation with yields of the rich meadow First, a system of drainage canals were made, which proved to be very successful immediately after commissioning. However, now there was no water for irrigation. According to Balif, the inhabitants of Gatačko Polje commented: “We do not need a cup without coffee”, i.e., drainage without irrigation means little. Because of that, construction of this part of the system continued. The most significant facility of this system is the Klinje Dam on the Mušnica River, 6.8 km upstream from Avtovac.

The dam site is located immediately downstream of the place where the Vrba and Dramešina (Ulinjski stream) streams merge, forming the Mušnica (Fig. 4.13). The geological structure of the dam site includes organogenic microbreccias, marly limestone and marls. The foundation pit in the riverbed is 4.4 m deep, and the height of the dam above the foundation is 22 m. It is an arched dam with a crest width of 4.6 m and a width of 16.7 m at the base (Figs. 4.13 and 4.14). The length at the height of the crest is 104.5 m, and the volume is 9504 m3. The dam body consists of an upstream and downstream cyclopean wall made of hewn stone, which rests on a 0.6 m thick concrete layer. The space between the upstream and the downstream wall is filled with broken stone that is filled with pozzolanic mortar. For the construction of the Klinje Dam, pozzolan (volcanic dust) was delivered from Naples. The volume of the reservoir is 1,730,000 m3, and the elevation is 1027 m. Water depth by the dam is 19 m. A tunnel in the right side is used for emptying the reservoir, 100.5 m cross section surface Ø = 7.56 m2. The diversion

4.4 Dams and Reservoirs

207

Fig. 4.13 Klinje Dam. From “Wasserbauten in Bosnian und Der Hercegovina—I Teil, Meliorationsarbeiten und Cisternen im Karstgebilte”, Wien, 1889

tunnel in the left bank is 125.2 m long, with cross section surface Ø = 8.64 m2 (Fig. 4.15). The melioration system in the field covered 575 hectares and consisted of a network of a main canal (29.1 km), then a secondary canal (29.0 km), a 65 km irrigating canal of small dimensions, 6 sluices (small dams), 81 water gates, 30 carts and 16 bridges for riders. Predicted was a later phase expansion of the melioration system towards Gračanica that would include a new 525 hectares. Balif imagined this expansion of the irrigation system would be done by the local population. To keep medium and small water as long as possible in Malo Gatačko Polje, the experimental installation of a small valve at the Kučina Ponor was carried out. The results of this experiment are not known, but it is known that works on this idea were postponed until land reclamation in Gatačko Polje was finished.

Much later, in 1971–72, the possibility of increasing the Klinje Dam height to 6 m was analyzed. This would be for water supply for the Gacko thermal power plant. Extensive exploratory works were carried out, including geological mapping and exploratory drilling through the body of the dam, with installation of double piezometers. These investigations, including a preliminary design, were done by the Institute for Utility and Protection of Karst Waters from Trebinje. (Fig. 4.16). The dam site is situated in limestone, which is dominated by Paleogene fauna. On the basis of drilling data, a geological cross-section was constructed. (Fig. 4.17). During the drilling of KL-4 and KL-5, dye was injected into the borehole and immediately appeared on the downstream face of the dam. The results of core tests from the boreholes showed that pozzolanic material has very poor

208

4 Water Resources Projects

Fig. 4.14 Klinje Dam, cross-section

mechanical characteristics. Since it was concluded that this is a very risky idea, it was abandoned. This is the oldest dam in this part of the Balkans, and it is still in operational condition. It is interesting to note that although an injection curtain was not constructed the dam has been in operation for more than 120 years without any losses (leakage). The dam was later repaired and was able to function as part of the system, together with the Vrba Dam and the Lazarići tunnel, to supply TPP Gacko with technical water.

4.4.2

Vrba Dam

Since the volume of the Klinje Reservoir does not satisfy the water supply needs of the Thermal Power Plant, the Vrba Dam was built, upstream from Klinje, on the Vrba stream. The project was fulfilled by Energoinvest from Sarajevo. This is a rock-filled dam, with an upstream waterproof reinforced concrete screen (Fig. 4.18). The maximum construction height of the dam is 43.70 m. The crest of the dam is at an altitude of 1065 m and has a width of 5 m. The foundation elevation of the dam body is 1021.30 m. The length in the crest is 221.90 m. A single-row grout curtain along the upstream perimeter of the dam foundation is 333.26 m long and from 22 to 36 m deep. Investigation works for the final design were carried

out in the period 1978/79–1980, and the dam was completed in 1982. The catchment area of the Vrba Reservoir is about 30 km2. The average annual flow is Qav = 0.904 m3/s. The reservoir volume is V = 14.6 × 106 m3 for a height of 1062.5 m. At the same time, it is the maximum elevation of a reservoir. Together, the downstream cascade (Klinje Dam and reservoir) and tunnel Lazarići form the water supply system for Phases I and II of TPP Gacko. The backwater rate for phase I is 1054.50 m a.s.l. and 1.063 m a.s.l. for phase II. Both the dam and the reservoir are located in an area of Cretaceous flysch, the so-called Durmitorski flysch. The dam site is located on the flank of the syncline. The right bank is built by limestone and the left by heterogeneous composition (marls and limestones). Based on water permeability tests (WPT), the investigated rock is defined as permeable. In one borehole (V-6), the presence of caverns was registered (from 11.5 to 14.6 m), as well as caverns in the limestone in the right bank. Measurements of seepage around the Vrba Dam were carried out in 1983. In April and in May 1983, the measured amount of water ranged from 90–1,48 l/s, for backwater elevation of 1060.10 m. The minimum measured flow of seepage (18.10.1983) is 88 l/s for the top water level of 1052.75 m a.s.l. (Fig. 4.19).

4.4.3

Gorica Dam and Reservoir

The Gorica Dam, on the Trebišnjica River, is located 3 km upstream from Trebinje (Fig. 4.20). It is a concrete gravity dam, with a construction height of 33.5 m, a length of crest 185 m, and with total reservoir volume of 15.6 million m3. Originally, the dam and regulation pool of Gorica served exclusively as daily leveling of water for HPP Dubrovnik and later, during the construction of RPP Čapljina, along with HPP Trebinje II. The dam site is located in the Upper Cretaceous bedded and thick-bedded limestones, with layers and lenses of dolomite. The strata dips towards the northeast, that is, from the left to the right bank. Investigative works (geophysics and boreholes) show that the karstification is well developed but relatively shallow (up to an elevation of approximately 200 m), in relation to the upstream and downstream parts of the Trebišnjica riverbed, where geophysical research (specific electrical resistance method) indicated karstification on a deeper level (Fig. 4.21). Since the regional Zupci fault crosses through the regulatory pool (Gorica Lake), there is a question of its hydrogeological role, i.e., possible seepage along it. It was finally concluded that this fault does not have any negative influence on the water permeability of the Gorica regulatory pool.

4.4 Dams and Reservoirs

209

Fig. 4.15 Klinje Dam with diversion tunnel outlet (Photo Milanović)

The grout curtain was not done in its entirety. In the right bank, only a part of the designed curtain was executed. Instead of the 449 m suggested by the design, only 200 m was finished. The length of the curtain under the dam is 170 m and 55 m on the left side. It is a double row grout curtain, with a distance between rows of 3.0 m and a distance between boreholes of 4.0 m. The upstream row is deep, 15 m, and the depth of the downstream row increases from 30 m below the left flank to 55 m below the right flank, following the limestone contact with dolomite. In total, 425 m of the curtain was constructed. The downhole procedure of grouting was applied, with a grouting mixture of 40% cement, 58% clay and 1.5% soda (Mikulec & Praštalo, 1965). The permeability of the dam site and especially of the wider area on the right bank is high, which manifested itself immediately after the first filling of the regulatory pool. On the base of investigative works, this high water permeability was expected. Depending on the water level in the pool, Fig. 4.16 Gacko. Klinje Dam. Position of piezometric boreholes and local groundwater connections (Milanović, 1971)

Fig. 4.17 Gacko. Klinje Dam. Geological cross-section along the dam axis (Milanović, 1971)

210 4 Water Resources Projects

4.4 Dams and Reservoirs

211

Fig. 4.18 Gacko. Vrba Dam. (a) Downstream face (b) Upstream faces with concrete slab. (Photos Milanović)

losses ranged from 1 m3/s at an elevation of 282.00 m to 3 m3/s at an elevation of 294.00 m (period 1965–1980). Because these losses are approximate equal to amount of minimum guaranteed flow through the downstream Trebinje urban area, it has been given up (temporarily) from the realization of the entire length of the grout curtain in the right bank. It is estimated that filtration through the ungrouted

sectin has no negative effect on the stability of the dam. Over time, losses have gradually increased, such as in 2003 when they increased from the 2 m3/s minimum up to 4.5 m3/s during a period when Gorica Reservoir (regulatory pool) was full— 294.5 m above sea level (Uljarević et al., 2003). The increase in losses at full reservoir amounts to 2.6 m3/s. This increase in losses clearly indicates the progressive

Fig. 4.19 Vrba Dam. Wier for seepage control, 2016 (Photo by Milanović)

212

Fig. 4.20 Gorica Dam and HPP Trebinje II (Photo Milanović, 1989)

Fig. 4.21 Gorica Dam. Temporary sluice to prevent excavation of dam foundation pit, 1962 (Photo by Mikulec)

4 Water Resources Projects

4.4 Dams and Reservoirs

213

Fig. 4.22 Progressive increasing of leakage around and beneath the Gorica Dam foundation from 1965 to 2003 (Uljarević et al., 2003)

erosion of the clay fill in the karst channels, and also possible degradation of the grout curtain (Fig. 4.22). Until 2009, the quantity of seepage water increased up to 4.80 m3/s (Zubac & Bošković, 2012). Losses from the Gorica regulatory pool are also evident through the ponor zone in the right side of the pool, 150 m upstream from the dam, and through the estavelle zone on the left side, approximately 540 m upstream of the dam (Fig. 4.23). By dye test of ponor zone, it was determined that filtration takes place around the curtain in the right side and shows up downstream from the dam site (Drenov do, Ržani do, to the piezometric borehole located in the unfinished part of the curtain and springs on the right bank, downstream from the dam site). Through the Gorica estavelle zone, on the left bank of the reservoir, there is constant loss of significant amounts of water; because of this, it has been the subject of interest and research for a long time. Tracer tests of the estavelle (1961 and 1964) showed that some of these waters discharge at the Lušac Spring in Police area and a part discharges at Oko Rasovac in Mokro Polje and in the Trebišnjica riverbed, downstream from the Gorica Dam. The presence of dye was also determined in the water samples of springs at the seacoast—Ombla, Zavrelje and Duboka Ljuta (Robinson)— which points to the existence of direct connections between the estavelle and these springs. An indirect connection is also possible with Ombla Spring because the labeled wave that flows from the surface of the Lušac Spring to the ponor zone in the Pridvorački river branch and from Oko Rasovac to the ponors in the Trebišnjica riverbed continues further towards Ombla Spring. Lušac Spring, which is a temporary spring under natural

Fig. 4.23 Area of Gorica dam site and Reservoir. Seepage from reservoir. Established underground connections

conditions, became permanent after the formation of regulatory pool Gorica. In order to reduce the losses as much as possible in the main opening of the estavelle, a one-way valve was installed, which allows discharge into the reservoir and prevents sepage from the reservoir (Fig. 4.24). The first geophysical tests using electrical mapping and charged body (mise a la masse) were performed in 1965. The aim of these tests is to indicate flow direction of sinking water. In the background of the estavelle, three investigation boreholes (E-1, E-2 and E-3) were drilled. With the same goal in 1981, geophysical examinations were carried out (method charged bodies, own potential and geoelectrical mapping). Geoelectrical mapping was carried out along profiles parallel to the reservoir (Fig. 4.25). It is noticeable that the results obtained in 1981 are almost identical to the results from 1965 so it can be said with great certainty that there are two concentrated directions of filtration of water that sinks in the Gorica estavelle zone. One zone with seepage flows, in downstream direction, is almost parallel with the reservoir bank, and other stretches toward the south.

214

4 Water Resources Projects

Fig. 4.24 Gorica estavelle 1. Gorica Reservoir level 2. Places of main opening of estavelle 3. One-way valve 4. Old railway traces 5. Direction of Trebišnjica River flow, 1985 (Photos Milanović)

In June 1985, the reservoir and the Gorica—Plat tunnel became empty, and construction of a grout curtain was started, 60 m long, in the hinterland of the estavelle. Works were mostly performed along an abandoned railway embankment (Fig. 4.26). Of the 21 boreholes that were drilled in the hinterland of the estavelle, 11 entered caverns of various dimensions, maximum up to three meters. Due to the short available time (only 15 days), the work was stopped. About 50% of the planned material for grouting effects on loss reduction were absent. For grouting repair of losses through the left flank, 10 investigation boreholes were drilled (1986) to a depth of about 70 m, between the estavelle and the inlet structure, for future head race tunnel II in HPP Dubrovnik. Seepage water under the dam significantly damaged the quality of contact between the foundation of the dam and the dam bedrock. An earthquake in the Montenegrin coast had a significant impact on 15.04.1979, when many cracks under the dam foundation were washed out. The water had a large percentage of clayey particles (muddy water) and water broth from foundation rock pieces of compact clay, weighing 0.5–1.0 kg. These pieces were squeezed out from cracks

and cavities when the seismic wave passed through the dam site area. Several hours after the passing of the seismic wave, numerous bubbles immediately downstream from the dam gave the impression of boiling water. In order to eliminate unwanted consequences for the dam, consolidation was carried out, and a part of the curtain under the dam was rehabilitated. In the period 2011/2012 a two-row grout curtain was built, which represents the first phase of the designed investigative rehabilitation works. With these works, apart from improving the dam/rock contact, seepage under the dam was reduced to Q = 0.250 m3/s (Zubac & Bošković, 2012).

4.4.4

Grančarevo Dam and Bileća Reservoir

Grančarevo Dam The double-curved arched Grančarevo Dam is located at the Trebišnjica River, 17 km upstream from Trebinje (Fig. 4.27). The construction height of the dam is 123 m, with the crest at an elevation of 403 m and a reservoir level at 400.00 m a.s.l. Construction of the dam created the Bileća Reservoir, with a

4.4 Dams and Reservoirs

215

Fig. 4.25 Results of geophysical (geoelectrical) investigations of the area behind the Gorica estavelle 1. Boreholes 2. Estavelle 3. Zone with possible underground circulation if supplying electrode is in the boreholes E-3 4. Zones with possible underground circulation if supplying electrode is inserted in the estavelle—1981 5. Same as in 4;

however, these measurements were done in 1965 6. Intensively karstified zone according to measurements provided in 1965 7. Intensively karstified zone according to measurements done in 1981 (Aranđelović, 1966 and 1981)

length of 18 km and a total volume of 1.277 billion m3. Construction of the dam began in 1959 and was completed in 1968, when final work on the overflow structure was done. The dam site is located in the northeastern wing of the Lastva anticline. The original location foreseen by the water management documentation, which is exclusively in the dolomites, was abandoned, and a new (existing) site was chosen, located 200 m upstream. The dam site is located in layered to banked Lias limestones, with marl-clay and clay-coal interlayers. The number of these layers decrease with depth and often deviate. Their thickness ranges from a few cm to 80 cm, but the existence of thicker layers cannot be ruled out. There are frequent lumachelle with lithiotis and zones of thin-plate limestones with thin bituminous zones. For the purposes of the project, 2800 m of exploratory boreholes were drilled, all of them in the left abutment, with the entire length in Liassic limestones. Most of the investigation boreholes in the right abutment are in dolomites. With investigation drilling and geophysical research, it was established that there is a more intense karstification of the

left abutment compared to right. The underground water level in period of minimum flow follows the base of karstification. The basic structural elements measurements of about 1200 points and appropriate statistical analysis were performed. Measurements show that it is a slightly folded structure that can be observed in an open outcrop, the right abutment downstream from the dam, as well as in the open quarry outcrop. Upstream of the dam site, the slope of the layers is from the left to the right abutment, with a general gentle dip upstream (WNW), between 10° and 20°; downstream from the dam, the slopes are even more gentle, between 6° and 15°. Analysis of the cracks shows that they are predominantly subvertical, with dominant direction of strike from east to west, that is, close to perpendicular in the direction of Trebišnjic canyon. Less frequent fissure systems are in the direction of the valley or with sharp angles in the valley direction. In the left abutment, all the boreholes remained in Lias limestones. Also, on the left side, more intense karstification was determined by geophysical investigations of the rocky

216

4 Water Resources Projects

Fig. 4.26 Grouting works behind the Gorica estavelle, 1985 (Photo Milanović)

mass, and drilling confirmed the presence of smaller caverns. By application of geoelectric sounding and mapping, it was determined that the slope of the bases of karstification in the left abutment agree with the inclination of the underground water slope. In order to prevent seepage and upward pressure on the dam foundation, a two-row grout curtain was constructed, with a distance of 3.5 m between the rows and a distance of 4.0 m between the holes. The upstream row of grouting holes is much deeper than the downstream row. The maximum depth of the curtain is 150 m, with a length of 664 m and an area of 64,000 m2 (Fig. 4.28a). The grout mix is based on clay: 65% clay and 35% cement, with an additive of 1.5% soda. Highly thixotropic grout components were used to seal the caverns: 66% clay, 33% bentonite and 1% soda. When this mixture did not give the expected results, a mixture based on 35% cement, 43% clay, 21% bentonite and 1% soda was applied. Consolidation grouting was performed with prior washing of all cracks in rocks under the foundation. Washing was

done in groups of three boreholes, in which washing sections of 5 m are separated by rubber packers (Fig. 4.28b). Into one borehole, water was pumped; into the second, air; and, through the third, or more of them if they are connected, washed clay material was discharged out. The washed cracks were then grouted with the cement mass. Many years of seepage monitoring show that the antiseepage works done around and below the Grančarevo Dam were successfully constructed. Seepage is less than 100 l/s, and often less of 50 l/s, because part of the water that flows through the control wier originates from precipitation downstream from the dam and the grout curtain but partially upstream from the wier. During the excavation for the foundations of the dam and the powerhouse hall (1963), a partly rock mass was separated and slid towards the riverbed along the clayey-marly interlayer. A wide crack was formed between the moved part of the rock mass and the bedrock (Fig. 4.29). The rock mass of approximately 8000 m3 was replaced with 6500 m3 of concrete (Stojić, 1966). In order to

4.4 Dams and Reservoirs

217

Fig. 4.27 Grančarevo Dam. (Photo Milanović)

permanently ensure the stability of the entire slope of the left side, prestressed anchors with a length of 40 to 70 m each, with a load capacity of 200 tons were used. Ninety such anchors were installed in the knots of the reinforced concrete grid (Fig. 4.29). After nearly 50 years of successful operation, some of the anchors that were damaged by corrosion were replaced (2014–2015). Apart from regular loading and unloading due to fluctuation of the reservoir, the dam experienced additional stress as a result of the earthquake in Montenegro (1979) and later (1980) during two experiments of dynamic forced vibration testing. During the second experiment, because of unexpected reactions of the dam, the test was interrupted and then abandoned, as it was deemed too risky.

Bileća Reservoir From the hydrogeological aspect, the wider area of the Bileća Reservoir can be divided into two zones that are characterized by certain individuality. One zone is the area of the reservoir banks and bottom, and the other is the

hinterland of the main spring zone. Position and geological characteristics of the left bank of the reservoir exclude the risk of water losses through rock masses in this area, opposite to the right bank, which is situated between the reservoir and the lower erosion base levels (Popovo Polje and Adriatic Sea). The terrain in which the Bileća Reservoir is situated is made up of dolomites of the Upper Triassic, limestones and dolomites of all Jurassic epochs, and Upper Cretaceous limestones and dolomites. All springs of the Trebišnjica River are submerged: Dejan’s cave, Nikšić springs and springs of Čepelica. When the reservoir is full, Dejan’s cave and Nikšić Spring are submerged by a 75 m column of water. Also submerged are the Oko cave, about 5 km downstream from the main spring zone, and several ponors, shafts and temporary springs, with a large maximum discharge. During investigation works, particular attention was paid to analysis of the hydrogeological functions of the dolomite core of the Lastva anticline (Fig. 4.30). This anticline has the

218

4 Water Resources Projects

Fig. 4.28 Grout curtain of the Grančarevo Dam. (a) Cross-section with permeability test results (b) Schematic presentation of consolidation grouting procedure and spacing of boreholes (c) Location of grouting boreholes 1. Reservoir elevation 2. Water table during dry period 3. Limit of the double-row grout curtain 4. Limit of the single-row

grout curtain 5. Upstream perimeter of the dam foundation 6. Check holes 7 Water under pressure 8. Washed out material 9. Compressed air 10. Unconsolidated portion of rock 11. Consolidated portion of rock (Stojić & Karamehmedović, 1970)

form of a recumbent fold that is partially overlaid to the southwest tectonic unit (Sikošek, 1954). The whole conception of Hydrosystem Trebišnjica was founded on assumptions about the watertightness of the right bank. This assumption is based on the role of the Lastva anticline as a regional hydrogeological barrier that enables creation of a watertight reservoir, which is the key facility of the entire system. This assumption was confirmed through numerous investigations: geological mapping, investigation drilling, observation of fluctuation GWL in piezometers, dye tracing of ponors in the reservoir space, boreholes in the right bank and geophysical examinations. Through dye tracing of ponors in the reservoir space, exclusive connections with springs inside of that space were established (O. Uzunović i J. Borudanović):

– Ponors near Parež are connected with the Oko Spring, upstream from the Grančarevo Dam, 1.4 km downstream. – Water which sinks in the Mlinica (Mill) ponor discharges in the same Oko spring near the Grančarevo Dam, upstream of the dolomite barrier.

– Water which sinks in the main spring area discharges 25 to 40 m downstream, in the Studenac Spring and the Brzak Buk Spring. – Ponors of the left branch of Čepelica Spring have a connection with permanent and temporary springs Lersko Oko, 2 km downstream. – Water which sinks near Tmuša discharges in the Oko Spring close to the Parež Dam, 1.77 km downstream.

Dye tracer tests of the piezometers in the right reservoir bank (1960–1965) confirmed a connection only with storage space (M-4 with Kopjela Spring, B-4 and B-8 with Herzegovina shaft). Through dyeing borehole B-2 (Jasen, 1959), a connection was established with Stara Mlinica (Old Mill Spring). This is understandable because it is a special sub-basin of the Trebišnjica right bank, which is not hydrogeologically connected with catchments of the right bank of the reservoir. Based on the results of all investigative works, professors M. Luković and B. Sikošek confirmed, in 1956, the validity of these assumptions, and the road toward further activities of the first phase of the hydrosystem was open. Positive hydrogeological function of the Lastva anticline was confirmed during the long operation time of the Bileća Reservoir. The results of multi-year observations of groundwater level fluctuation indicate that there is a good hydraulic

4.4 Dams and Reservoirs

219

Fig. 4.29 Grančarevo Dam, left bank. Left photo—large crack created due to sliding of separated rock mass (Photo documentation HET, 1963). Right photo—concrete grid with reinforced anchors that improve stability of left abutment (Photo Milanović)

connection between the reservoir and the karst aquifer on the right bank (Fig. 4.31). In part of the aquifer, which is closer to the reservoir, fluctuation of GWL absolutely corresponds to the water level in the reservoir, regardless of current hydrological conditions and the trend of oscillating levels in the reservoir (filling or emptying). This is clearly visible on the hydrogram of piezometer M-4, which is about 2 km away from the reservoir. The deeper aquifer is under the influence of the reservoir; however, it is also under influence of local hydrogeological conditions. Its level is always higher than the reservoir level. So, in the distant parts of the aquifer in the right bank (area of piezometers B-2 and B-4), due to complex lithostratigraphic features and tectonic structure, the influence of the reservoir is variable. Even in natural conditions and after formation of the reservoir, it is always above the elevation of 360 m. When the reservoir level is lower than 360 m a.s.l., there is restoration of the natural condition of that part of the aquifer.

During a period of intense rainfall, there is a sudden increase of the level in B-2 and B-4 and somewhat slower lowering. Then, the GWL in B-2 is up to 20 m lower than in B-4. The cause of these anomalies can be charging of the piezometer independently from the local GWL. The real possibility of temporary local shifting of the watershed during extremely high precipitation, in periods of high reservoir levels, should kept in mind. Applying geoelectric sounding to the right bank, with two depths, corresponding to elevations of 300 to 400 m, there are separated zones of this bank that are weakened (karstified) rock mass, in terms of water permeability (Fig. 4.32). From the aspect of water permeability, of special importance are the zones that extend from the area of Dubočani and Orah towards the downstream part of Trebišnjica, between Stara Mlinica and the place where the Zupci fault crosses the riverbed. During the long period of operation of the reservoir, no phenomena that indicate such a possibility were registered.

220

4 Water Resources Projects

Fig. 4.30 Right bank of Bileća Reservoir and position of dolomites of Lastva anticline 1. Karstified limestone 2. Dolomites 3. Anticline axis 4. Large permanent spring 5. Large temporary spring 6. Small temporary spring 7. Small permanent spring 8. Ponor 9. Riverbed 10. Regional discontinuity 11. Overthrust 12. General direction of underground flows 13. Borehole (Milanović, 2006)

4.4.5

Upper Regulatory Pool Hutovo (Hutovo Reservoir)

The Hutovo Reservoir functions as the upper regulatory pool of the Reversible Power Plant (RPP Čapljina). It was formed by the construction of an embankment dam downstream from the Ponikva Ponor, that is, from the last point of the Trebišnjica riverbed. The rock-filled dam (embankment) is long, 492 m, and it has a height of 10 m. Waterproofing of the embankment provides a clay core from the material in the regulatory pool area (Fig. 4.33).

With an elevation of 230 m, the surface of the pool is 68 ha, and the volume is 5.5 million m3. By increasing the clay core with a clay-concrete diaphragm, the operational height is increased to 231.50 m a.s.l. and the volume increases to 6260 million m3. The canal part stores 0.59 million of water. The reservoir is connected with a siphon-type connection tunnel through the Klek ridge, with a head race canal, i.e., with a canalised Trebišnjica riverbed through Popovo Polje. The last 10 km of the canal gradually expand and is protected by embankments, so it becomes part of the storage area.

4.4 Dams and Reservoirs

Fig. 4.31 Ground water level hydrographs of Bileća Reservoir—right bank 1. Reservoir water level 2. Boreholes 3. Reservoir water level hydrograph 4. Hydrographs of piezometers B-2, B-4 and M-4 5. Fault 6. Overthrust front Precipitation hyetograph (One bar represents

221

precipitation for 48 h period) 8. Bileća Reservoir 9. Surfaces covered by loose overburden 10. Dolomites 11. Limestone 12. Local fluctuation of piezometric levels (Milanović, 1981)

222

4 Water Resources Projects

Fig. 4.32 Right bank of Bileća Reservoir. Contour map for the bases of karstification 1. Contours for the bases of karstification 2. Impoundment limits by the reservoir at elevation 400 m 3. Possible directions of water loss from reservoir (Aranđelović, 1970)

Where the canal leaves the route of the Trebišnjica riverbed, three free overflows are constructed, across which water flows toward the Ponikava, Lisac and Crnulja ponors (Fig. 4.34). The regulatory pool (Hutovo Reservoir) is located in the lowest part of Popovo Polje, in the northeast wing of the anticline structure (so called Zelenikovac anticline) which is

built of Cretaceous limestones. The core of this anticline consists of Lower Cretaceous dolomites. They function as a hydrogeological barrier, toward the Adriatic Sea. This is confirmed by investigation boreholes and numerous tracer tests (Fig. 4.35). In natural conditions, the very end of Popovo Polje (now the Hutovo Reservoir) was connected by a natural channel

4.4 Dams and Reservoirs

Fig. 4.33 Regulatory pool Hutovo (Hutovo Reservoir)

223

224

4 Water Resources Projects

Fig. 4.34 Regulatory pool Hutovo with part of head race canal for RPP Čapljina

with Zablatak (Vrutok). A built stone partition (Hadžibeg gap) is in the channel, with an opening that can be closed with wooden planks (Fig. 4.36). In monograph Geomorphology II, 1926, J. Cvijić shows a sketch of this part of the Popovo Polje, which today results in regulatory pool RPP Čapljina (Fig. 4.37). The lowest part of Popovo Polje, near Hutovo, is covered with alluvial sediments whose thickness reaches 30 m in the middle section. The paleo-relief has all the properties of typical karst morphology, with a large number of sinkholes and ponors. Although alluvial deposits contain a large percentage of clay (25%–30%), these sediments are very permeable. They are formed predominantly by suspended particles, which are transported with flood water and deposited over vegetation that grows in interflood periods. After the decomposition of this vegetation in clay-sand alluvial sediments, numerous tubes (pseudo-loess structures) remain, through which the water percolates towards karstified paleo-relief. Next to that, inside of the reservoir space, 89 ponors in alluvial sediments are registered, through which there is concentrated water seepage. These ponors are mostly registered in zones where the alluvium depth does not exceed 10 m. The largest of the ponors are created in the form of collapsed sinkholes (see Sect. 1.6.1 Popovo Polje, Fig. 1.36). Total losses through this part of the bottom of Popovo Polje were from 8 to 12 m3/s, depending on flood level and sinking conditions. During each flood, some of the ponors

were naturally closed, and new ones were created. Also, some ponors were closed by the locals, but that usually did not produce long-lasting effects. In order to ensure the watertightness of the regulatory pool, extensive investigative works were carried out and specific geotechnical measures were undertaken. Along with detailed geological mapping, an extensive program of investigative drilling and geophysical research was carried out, with numerous soil mechanic tests, speleological research of surrounding shafts and ponors, TV logging of boreholes, stereo photography in boreholes, and excavation of individual ponors to the karstified paleorelief. Numerous tracer experiments were performed, using Na-fluorescein, radioactive isotopes and smoke tracer for examination of the unsaturated zone. To make tracer investigations during the flood period possible, boreholes GH-4 and the Ponikva Ponor were equipped with montage towers (Fig. 4.38). Two technical possible solutions to achieve the required watertightness were analyzed: – making underground anti-filtration barriers (grout curtain) – utilizing surface treatment to achieve watertightness of the reservoir floor In order to determine the spatial position of the karst channels through which water is drained in Ponikva, Žira and Kaluđerov ponors, i.e., to determine underground

4.4 Dams and Reservoirs

225

Fig. 4.35 Hutovo Reservoir 1. Karstified zones with undeground flow 2. Axis of Zelenikovac anticline 3. Boreholes 4. Large ponor 5. Direction of underground flows (Milanović, 1971, supplemented)

Trebišnjica flow under the dry valley between Popovo Polje and Hutovo village, two deep boreholes were drilled (profiles H and HB, Fig. 4.39). The depth of these boreholes varies between 150 and 250 m. With these borehole and tracer tests, with short half-life decay of radioactive isotopes (Br-82 and Cr-51), it was determined that water from the reservoir area very quickly reaches a great depth after sinking and that there are two levels of active karst channels. Isotopes were injected into the Ponikva and Žira ponors (Fig. 4.40). At the same time as the injection of isotopes, measurement of radioactivity was started inall boreholes. In the Fig. 4.41, there are diagrams of radioactivity for boreholes H-6 and HB-3. In the profile along the underground flow (Fig. 4.42), immediately after injection into Žira and Ponikva ponors, water reaches a depth up to 150 m.

Immediately after sinking, the gradients are large, so the flow speed is also exceptionally fast, from 30 to 50 cm/s. The remaining part of the flow, towards the Neretva valley, has a flow velocity that is considerably slower (between 1 and 6 cm/s). With these investigations, approximate contours (width and height) of zones with concentrated flows (picture 4.43, profile H-2–H-11) were determined. In addition, some boreholes entered caverns of considerable dimensions. Borehole H-4 penetrated into a cavern over 30 m deep (from 140 to 170 m above sea level). The last depth of these caverns and the rest of the characteristics are unknown. The connection of karst channels in the aeration zone below the bottom of the Hutovo Reservoir was determined using a smoke tracer. Through the overflow shaft into the Ponikva ponor, smokes boxes were inserted and, using three strong fans, air circulation in aeration zones was established. The total power of these fans was 35 KW, and the air flow

226

4 Water Resources Projects

Fig. 4.36 Very end of Popovo Polje. Ruins of ancient water gate, 1969 (Photo by Milanović)

was 21 m3/s. About 350,000 m3 of air was pumped into the ponor and was registered in boreholes AD-4 and A-1 and aeration pipes AF-1 (Fig. 4.43). The distance between Ponikva Ponor and aeration pipe AF-1 is 1100 m. The speed of the smoke stream from aeration tube AF-1 was 5.5 m/s (Bagarić et al., 1980). Part of the air and its smoke erupted from the cracks surrounding the ponor. A similar experiment was performed on aeration pipe AF-1, which was installed in the karst channel under approximately 10 m of alluvial cover (Fig. 4.44). After 10 h and 8200 m3 of pumped air underground, the labeled wave appeared from borehole A-15, situated at the reservoir bank. Through analysis of the results of all the mentioned research, the conclusion was that the option of underground sealing is very risky, so it was decided to utilize surface sealing. There were three basic technologies for sealing selected:

– compacting surface layers of alluvial sediments – blanketing by PVC foil – coveringthe rocky banks by shotcrete

Ponor zones were filled by aggregate (reverse filter), covered by compacted clay and, finally, protected by PVC foil. Remediation of the most important ponor zone in limestone, under alluvium, was done by grouting from the surface. Investigation drilling (Fig. 4.45), revealed the borehole network at the bottom of the reservoir, not far from the intake structure (sink zone shown in picture 1.36). There was the existence of a large funnel-shaped ponor and channel through the alluvium, in which there is an active karst channel in the limestone paleo-relief, at a depth of approximately 50 m. First, there was grouted karstified limestone, including a karst channel, and then part of the channel situated in alluvium was filled with grout mix. At the surface, the entire structure was protected by a compacted clayey layer and was covered with PVC foil. Strong air flow was measured in piezometers AD-1, AD-4 and A-5 in the reservoir bank. This flow reaches a speed of up to 15 cm/s (Skopljak & Kovačina, 1978a). Measurements on the top of pipes established that, in some cases, air flows out from the borehole; however, after 15–20 min, air was sucked (vacuumed) into the borehole (Fig. 4.46). This periodicity is

4.4 Dams and Reservoirs

227

Fig. 4.37 End section of Popovo Polje. Sketch made by Cvijić in 1926 and present situation. (Photo Milanović)

more pronounced at lower water levels in boreholes; however, with an increase of GWL, this gradually reduces. In the chapter on Popovo Polje—ponors (1.4.1), it is explained that ponors generate because of pressurised air in a period of sudden increase of GWL. During flow investigation works in the area of regulatory pool Hutovo, this phenomenon was registered a fewtimes. This is confirmed in the physical model. Negative consequences of this phenomenon

were registered after the first filling of the reservoir and the first intense rainfall. Due to very fast rising of GWL, the air in the karst channels comes under pressure and demolishes the PVC foil (Figs. 4.47 and 4.48). To prevent that kind of destruction of watertight structures, aeration pipes were constructed that enable unhindered air circulation. However, only an aeration pipe that is

228

4 Water Resources Projects

Fig. 4.38 Hutovo Reservoir. Investigation structure above borehole GH-4 and, in corner, above Ponikva Ponor, 1970. (Photos P. Milanović)

installed directly into the ponor opening in paleo-relief can work properly (Fig. 4.49). Proper installation of aeration pipes is possible by excavation through alluvial sediments, only. Aeration pipes which are embedded by drilling through the alluvium from the surface, in the majority of cases, donot establish contact with the aeration zone and do not function in a satisfactory way. This is because the opening of the karst channel in paleo-relief is almost never located exactly below the collapsed ponor at the surface. Origin balloons and foil damage from air pressure due to fast increases in the level of underground water is schematically displayed in Fig. 4.50. Damage to the foil can also occur due to underpressure created in the aeration chamber zone, as a consequence of the sudden descentof underground water levels (Fig. 4.51). During inspections of the reservoir floor in 1976/77, along with newly created ponors new phenomena in the form of cracks in compacted alluvium were registered (Fig. 4.52). The cracks were also formed under the PVC foil. The width of the crack ranged from 1 to 15 cm, and the length from a

few meters to a few tens of meters. At some cases the width of individual cracks reached 20 up to 30 cm. Locally, two parallel cracks formed, at a distance of 20–30 cm, and part of the terrain between them sank from a few cm to 0.5 m. The visible depth of the cracks was from a few decimeters to 5–6 m. The total length of these cracks was 1300 m. Along some of cracks, ponors were created. They are usually ponors with a smaller diameter, from 0.3 to 1.0 m, mostly created at the intersection of two cracks. The presence of cracks was previously observed during the emptying of the reservoir, when the bottom is still covered by 1–2 m of water, which means that they were not formed as a result of drying clay-sandy sediments. The cracks are repaired by filling them with a clay-cement mixture. Locally, there were accidents in the shotcrete blanket on the bank of the regulatory pool (Fig. 4.53). This happened in places where the shotcrete was applied over the opening of the karst channel (ponor) and which was not adequately rehabilitated, so it came under concentrated uplift pressure. For the rare cases of large inflow through Popovo Polje, when the lowest part of Popovo Polje may be threatened by

4.4 Dams and Reservoirs

229

Fig. 4.39 Investigation H and HB borehole profiles in the Hutovo area. 1. High level zones with groundwater flow 2. Low level zones with groundwater flow 3. Boreholes with mark and collar elevation (Milanović, 1976)

flooding, the ponors of Doljašnica and Ponikva have been used as overflow, for the evacuation of these waters. At the junction of the canalised riverbed of Trebišnjica and the earlier dug up canal to the Doljašnica, a structure was built, with a water gate for regulated drainage of excess water (Fig. 4.54). Ponikva Ponor is arranged like a shaft overflow (Fig. 4.55). The natural opening of the ponor is plugged with a concrete plug, for draining floodwater that appears in extreme cases, and a 3.0 m diameter shaft was excavated to the karst channel. To make runoff possible through Ponikva Ponor, which would begin immediately with overflow on the upstream side, ahorizontal gallery to the vertical shaft was excavated, and the entrance was protected with a steel grid. At the time of the first rehabilitation of the riverbed (1975), the polje flooded and unusual situations occurred— the reservoir was empty and dry, and the space out from the reservoir was submerged by water (Figs. 4.56 and 4.57).

4.4.6

Lower Regulation Pool Svitava

For needs of the Čapljina Reversible Hydropower Plant, of 1340 ha in the Svitava depression (swamps), 1000 ha was converted in the lower regulatory pool, with a volume of 44 hm3 (Fig. 4.57b). The pool was formed by construction of the Krupa Dam and embankment along the Krupu River, with a length of 1.861 m, and branches toward the perimeter canal, the length of the embankment being 1680 m. Three sides of the regulatory pool Svitava (Svitava Lake) are created by embankments. Only along the northeast does the reservoir rest directly on the limestone of the Ostrovo ridge that separates Svitava and the Derane cryptodepression. The water level in Svitava Lake is always 1.5 m to 2.5 m higher than the level in Deran Lake, but a hydrogeological connection through the ridge does not exist. Level fluctuations of the lake range between elevations of 3.20 and 3.35 m (15 cm). Very rarely, the level drop s to an

230

4 Water Resources Projects

Fig. 4.41 Graphs of radioactivity 1. Radioactivity of labeled water flow 2. Natural radioactivity along the boreholes Fig. 4.40 Injection of radioactive isotope Br-82 into the Ponikva Ponor, 1971 (Photo Milanović)

elevation of 3.0 m or rises up to 3.45 m a.s.l. The level of the Krupa River varies between 0.70 m above sea level in the dry season and 1.79 m above sea level in the rainy season. The extremely low level of the Krupa River (0.65 m above sea level) was registered on July 16, 2007. On the same day, the level of Svitava Lake was 3.26 m a.s.l. Due to poor soil mechanics characteristics, with a large percentage of peat, subsidence occurred along the embankment during construction (up to 2.67 m), and later, in the years after the release of power plants in operation but to a significantly lesser degree.

4.4.7

Dam and Alagovac Reservoir

The Alagovac Dam in Nevesinjsko Polje was built on the stream of the same name, which sinks into the Ždrijelo Ponor. It was completed in 1962. The total height of the dam is 22.85 m. Height above the ground is 13.85 m. The length of the dam is 230 m. Reservoir volume is 3.6 million m3, and the surface area is 43 ha. The dam body is built from sandy and gravel loam. The dam is founded on gray watertight clay. The

catchment area of Alagovac is evaluated at 20 km2, (according to B. Đerković 18 km2, 1966). The purpose of this reservoir is to supply water for the Nevesinje urban area; however, many problems limit the efficiency of this structure.

4.4.8

Bukov Creek: Potential Reservoir

In spite of huge yearly precipitation, the usability of significant agricultural areas in Ljubinjsko Polje is limited due to lack of water in the extremely dry vegetation period. The only stream that passes through the polje and ends in the Konac Ponor zone is Bukov creek. During the vegetation period, the stream dries up completely along its length. Basic hydrological and hydrogeological data of Ljubinjski Polje and Bukov creek are given in Sect. 1.6.6. The possibility of constructing a dam and reservoir in the dolomites of Bukov creek has been analyzed a few times over the past 65 years. The goal of this intervention is to accumulate a sufficient amount of water in the winter period for the needs of irrigation in the dry period of the year, which coincides with the vegetation period.

4.5 Tunnels

231

mapping of the terrain was carried out, along with three boreholes, two with a depth of 30 m, and one with a depth of 20 m. According to the project, the dam would be embankment (filled), with a height of 44.5 m, with a reservoir elevation of 777 m. Reservoir volume is 3.5 million m3. Dam construction was foreseen to be in stages. Because of the impossibility of financing, the project was not realized. Due to the need for water in 1983, the idea of utilizing Bukov Creek was reactivated. The Institute for the Use and Protection of Karst Waters from Trebinje programmed and began investigative works. The dam site was selected, limnigraph was installed and investigation drilling of three boreholes was executed. However, meanwhile a pipeline for water transport from Bregava springs to the Ljubinje town and realization of reservoir in Bukov creek was in no hurry. This one possibility is again considered and analysed in 1994 (Energoprojekt, Belgrade). It was estimated that total available water potential is 42 l/s. By construction of dam height 40 m and with reservoir elevation of 773 m is possible to have reservoir with volume of 2.2 million m3. To improve watertightness of reservoir by application of necessary geotechnical remediation should be covered surface which amounts to 12%–15% of the reservoir area. The catchment area until dam site is approx 10 km2 situated mainly in dolomites of wider Krtinje area. In period 2019/2020, on Bukov creek, immediately after entry to Ljubinjsko Polje, a dam was built in alluvial sediments. The bottom and the sides of this accumulation pond are coated with a geomembrane.

4.5

Fig. 4.42 Position of underground flows in the area of Hutovo Reservoir. (a) Natural flood level in Popovo Polje (b) Large ponor at the perimeter of Popovo Polje (c) Large ponor below the alluvial deposits (d) Lower underground flow (e) Piezometric boreholes (f) Alluvial deposits (g) Higher level of groundwater flow (K) Cavern (R) Borehole section where groundwater flows labeled with Br-82 and Cr-51 flowing around (Milanović, 1976)

The dam was mentioned for the first time in 1960 in the document “Meliorate-energy system in East Herzegovina”. This idea was formed from the results of geological prospecting of the terrain (Bukovo do), which was carried out in 1957. In the period 1960–1967, execution of the Bukovi do dam was carried out (Prof. D. Milovanović with associates, Civil engineering faculty Belgrade). Geological

Tunnels

Under this heading, a general description of the problems tunnel builders faced in the area of East Herzegovina and Dubrovnik Littoral is presented. The majority of these problems occurred as consequences of karstification of the rocky masses, including the presence of numerous caverns and karst channels along the routes of tunnels and bursting out of underground water during the excavation, but also damage to the lining caused during the operation of the tunnel. The largest caverns represented a particular problem during tunnel excavation with a tunnel boring machine (TBM), a so-called mole. These experiences will be used in future tunnel works in karst. By length and diameter, head race tunnels for HPP Dubrovnik, HPP Dabar and RPE Čapljina dominate. The Dabar-Fatnica, Fatnica-Bileća and Lazarići tunnels are used for conveying water. With the construction of PP Bileće, the Fatnica-Bileća tunnel becomes a head race tunnel. The purpose of the tunnel in Konavosko and Bilećko poljes is exclusively for drainage of flood waters.

232

4 Water Resources Projects

Fig. 4.43 Hutovo Reservoir. Connections in aeration zone established using smoke tracer 1. Shotcrete blanket 2. Head race tunnel 3. Boreholes 4. Aeration tubes 5. Connections established by smoke tracer 6. Ponor (Bagarić et al., 1980)

Fig. 4.44 Injection of smoke tracer through aeration pipe AF-1 into the aeration zone, beneath the bottom of Hutovo Reservoir (a) 1. Aertion pipe 2. Fan 3. Smoke cans (b) Monitoring of smoke and air current from aeration pipe. (Photos Milanović, 1980)

4.5 Tunnels

Fig. 4.45 Plugging of ponor beneath the alluvial sediments in the Hutovo Reservoir. (a) Grid of investigation/grouting boreholes and topography of paleo-relief. (b) Cross-section A—A’ crossing the ponor beneath alluvial deposits. 1. Karstified limestone 2. Alluvial deposits with prevailing clayey particles 3. Alluvial deposits with

Fig. 4.46 Diagram of cyclic changing of air current direction from piezometric borehole A-5 during rapid water level increasing. (Skopljak, Kovačina, 1978b)

233

prevailing sandy component and limestone block 4. Active karst channel 5. Underground flow direction 6. Sinkhole type of ponor at the surface 7. Investigation—grouting boreholes 8. Compacted layer 9. Depth of grouting (Milanović, 2003)

234

4 Water Resources Projects

Fig. 4.47 The large foil balloon as a consequence of pressurized air from underground

4.5.1

Tunnel for Konavosko Polje Drainage

The purpose of this tunnel is to drain the Konavosko Polje. The tunnel was excavated through a limestone- dolomite ridge between Konavosko Polje and the seacoast, a length of 1944 m and with a capacity of 65 m3/s. Three quarters of the tunnel is located in Upper Cretaceous dolomites (Fig. 4.58). The tunnel passes through 13 caverns, mostly in dolomites. The volumes of individual caverns exceeded 1000 m3 (Roglić & Baučić, 1958). For example, a tunnel passes 35 m in the middle of the cavern between chainage 0 + 903 and 0 + 938, but on chainage 0 + 1370, the eastern wall of the tunnel cuts through the cavern, a large part of which is located outside the tunnel route (Fig. 4.59). The longer axis of this cavern exceeds 55 m.

Caverns are mostly filled with clayey material and carbonate blocks, and there is periodic collapsing of materials. Because of this, there is periodic cleaning and remediation required in endangered locations in the tunnel.

4.5.2

Access Tunnel for HPP Dubrovnik and Tail Race Tunnel II

During excavation of the access tunnel for the Dubrovnik underground hydropower plant in Plat, an active karst conduit system of the Robinson Spring was cut (Fig. 2.53, chapter on Duboka Ljuta—Robinson). On the route of the access tunnel, at chainage 0 + 396 to 0 + 401 m from the coast of Župa Bay (1956), a cavern was found in the Triassic dolomites. In a period of heavy rainfall,

4.5 Tunnels

235

Fig. 4.48 The foil demolished by strong air pressure (Milanović, 2006)

excavation works had to be suspended several times due to floodwaters that flowed through the access tunnel (Fig. 4.60). A part of the same karst system is also registered on the trace tail race tunnel II of the hydropower plant Dubrovnik. Speleological mapping of this system was done from 1959 to 1968 and later, in 1999. Since the channels are located at sea level, the mapping was made with the help of rubber boats in 1969. Several transverse profiles, where tunnel II crosses the karst channel, are shown in Fig. 4.61 (Gašparović, 1979). A burst of water from the underground channel into the access tunnel occurred several times when the power plant was in operation.

4.5.3

Gorica - Plat Tunnel (Head Race Tunnel for HPP Dubrovnik)

The length of this tunnel is 16.57 km, and it has a diameter of 6.60 m. After concrete lining construction diameter is 6.00 m. In Mokro Polje near Rasovac, the tunnel breaks out on the surface and a half-buried reinforced concrete pipeline goes to Crnač, at a length of 1162 m, 5.4 m in diameter. The route of

the tunnel passes through the Cretaceous and, in a smaller part (closer to Plat), Jurassic limestone (Fig. 4.62). In the investigative phase, in addition to detailed geological mapping, geophysical methods were also applied: electrical mapping and sounding, as well as the refraction seismic method. Geoelectric mapping along the tunnel route was carried out along three parallel profiles to a distance of 100 m. After excavation was finished, the rock mass along the tunnel was investigated using microseismic mapping and refractive seismic method. Numerous cavernous and fault zones were cut with the tunnel, but large caverns were not detected. In the first section, on the left side of the Gorica Dam, caverns were cut at chainage 0 + 090, 0 + 120 and 0 + 216. Through dye tests of the Gorica estavelle and caverns (ponors) at chainage 0 + 216, it was determined that part of the waters that sink in the left side of the reservoir pass through that cavernous zone. They discharge downstream in the Trebišnjica riverbed and partially flow through underground towards Ombla and Zavrelje springs (Fig. 4.24). By geological mapping, a few smaller caverns are registered along the tunnel. Most of these caverns are filled

236

4 Water Resources Projects

Fig. 4.49 Hutovo Reservoir. Aeration pipe. 1. Reservoir water level 2. Aeration pipe 3. PVC foil 4. Compacted layer 5. Alluvial sediments 6. Karstfied limestone 7. Karst channel 8. Concrete 9. Water table 10.

Direction of air current during water table decrease 11. Direction of air current during water table increase (Photo and sketch Milanović, 1986)

with gray clay, sandy clay and red clay, while empty caverns are rare. A few larger caverns were also registered, which are filled with clay and limestone blocks of various sizes. These caverns are mostly related to more significant tectonic zones. More significantly, caverns are registered at the following chainages:

– 11 + 445 to the 11 + 451 caverns filled with clay – 16 + 506 to the 16 + 514 larger cavern filled with sandy clay.

– 3 + 700, cavern in calota diameter 5.5 m, filled with terra rossa, – 6 + 761 to 6 + 767 larger cavern, – 9 + 827 to 9 + 870 tectonically damaged zone, along which water previously circulated forming a large cavern which was subsequently filled with green clay with blocks and pieces of limestone, – 9 + 917 to the 9 + 925 cavern filled with clay, – 10 + 485 to the 10 + 500 cavern, formed along tectonic crushed zones, filled with gray clay with blocks of limestone,

During excavation (1960–1963), work was often suspended due to a burst of larger amounts of water from the caverns that the tunnel cut through. The excavation was interrupted a total of 25 times, due to flooding (full profile) that occurred after heavy rainfall. Because of these floods, works were suspended for a total of 160 working days. In these cases, tunnel had the role of artificial drain, in which the inflow was more than 2.5 m3/s. It is significant to note that, along the greater part of the tunnel route, a maximum level of underground water was deep below the tunnel level. Each fault zone or cavern filled with clayey material had as consequence disorder of designed excavation technology. That situation considerably affected the working efficiency during days after occurrence.

4.5 Tunnels

237

Fig. 4.50 Destruction of PVC foil under air pressure 1. PVC foil 2. Rock filling (inverted filter) 3. Compacted layer 4. Karstified limestone 5. Alluvial sediments 6. Karst channel 7. Water level 8. PVC foil under pressure 9. Reservoir water level (Milanović, 1986)

Fig. 4.51 Destruction of PVC foil by subpressure 1. PVC foil 2. Compacted layer 3. Alluvium 4. Suffusion cavities in alluvium 5. Part of channel with collapsed-in material 6. Karstified limestone

7. Karst channel 8. Lowering of water table 9. PVC foil 10. Subpressure direction 11. Loading of foil due to water column 12. Reservoir water level (Milanović, 1986)

238

Fig. 4.52 Defects at the reservoir floor detected after first reservoir filling. (a) Large fissures at the compacted bottom of a reservoir (b) Ponors (collapses) created along the sagged part of soil between two

4 Water Resources Projects

close fissures (c) Fissures under the foil (d) Collapse (ponor) provoked by boreholes (Milanović, 2003)

4.5 Tunnels

239

Fig. 4.53 Destruction of shotcrete blanket at the reservoir bank, as a consequence of inappropriately plugged ponor and strong groundwater uplift (Milanović, 2006)

Fig. 4.54 Overflow structure Doljašnica. 1. Water gate 2. Doljašnica Ponor 3. Alluvium 4. Limestone 5. Trebišnjica River 6. Canal towards Doljašnica Ponor

240

4 Water Resources Projects

Fig. 4.55 Overflow shaft at Ponikva Ponor 1. Flood level in extreme cases 2. Overflow shaft 3. Concrete plug at Ponikva entrance 4. Karstified limestone 5. Ponikva channel with deposited sediments

6. Sediments in front of entrance in horizontal adit 7. Protective steel grid above the shaft entrance 8. Horizontal adit with protective steel grid at entrance (photo)

In total, due to floods and excavations in fault and cavernous zones, there were 35 disruptions to designed excavation technology. With the excavation of the tunnel, numerous channels with vertical circulation were reactivated, which had an indisputable influence on the stability of the concrete lining, due to large external pressures. These pressures cause major damage to the lining during tunnel operation. The consequences of these damages are large losses from the tunnel that reach 1200 l/s. Their rehabilitation requires large-scale works every 3 to 5 years. Heavy rains that fall during the rehabilitation works cause such an inflow of water that urgent evacuation becomes necessary for everyone present in the tunnel. During regular annual inspections of the tunnel, it was established that all the defects of the lining occurred in zones with caverns.

4.5.4

Fatnica - Bileća Tunnel

The route of the tunnel that connects the temporarily flooded Fatničko Polje and the Bileća Reservoir passes through highly karstified Cretaceous limestone. The length of the tunnel is 15.64 km, and the diameter is 7.1 m. In this stage of construction, the purpose of the tunnel is to transfer the waters of the Upper Horizons into the Bileća Reservoir. Because of this, the tunnel is not lined, except for local concreting of the cavernous zones. During the final construction stage of the Hydrosystem Trebišnjica and implementation of HPP Bileća on the bank of the Bileća Reservoir, the tunnel becomes a head race, which will require its lining. The exit of the tunnel and the place for the future HPP Bileća near Čepelica is shown in Fig. 4.63.

4.5 Tunnels

241

Fig. 4.56 Floodwater out of the Hutovo Reservoir. The reservoir space is dry. (photo by Milanović, 1975)

Fig. 4.57 Hutovo Blato wetland. (a) Krupa sluice (b) Regulatory pool Svitava with floating peat islands, 2009 (Photos Milanović)

The route of the tunnel is in the zone of a large karst aquifer, through which the catchment area of the Trebišnjica spring is drained, that is, the catchments of Gathačko, Cerničko and Fatničko Poljes. Numerous investigative works have shown that circulation takes place through high permeability channels, with a velocity of underground flows of up to 13 cm/s. The direction of the tunnel matches with the

general direction of underground water flows that sink in the Pasmica ponor zone. Since major problems were expected during excavation (both hydrogeological and of a geotechnical nature), extensive research was undertaken along the route of the tunnel. With detailed geological mapping, with the corresponding prognostic cross-section, geophysical investigations were

242

4 Water Resources Projects

Fig. 4.58 Tunnel for Konavosko Polje drainage 1. Cretaceous limestone 2. Cretaceous dolomites 3. Alluvium 4. Caverns (Roglić & Baučić, 1958)

carried out along the tunnel route (geoelectrical mapping and sounding), as well as boring investigation/piezometric boreholes in several locations (Fig. 4.64). Excavation started at three places: – Inlet site Pađeni between chainages 0 + 000 and 4 + 017 and lateral subsection (side excavation 0 + 000 to the 0 + 830 km), without possibilities for gravity drainage – Inlet place Podtuhor in Bilećko Polje from chainage 4 + 017 to 12 + 632, with the possibility of gravity drainage – Inlet site Čepelica from chainage 12 + 632 to 15 + 649 and possible gravity drainage The longest section, from the Podtuhor upstream, was done with a tunnel boring machine (TBM). As expected, the problem of overcoming caverns and floods was permanently present during tunnel excavation. Along with the problem of intense karstification the contractors already faced with the excavation of the intake structure in Fatničko Polje. The presence of numerous caverns significantly slowed down the progress of the TBM. Not longer than 70 meters in certain sections, the TBM had to overcome 5–7 caverns. Supplementary geophysical research and reinterpretation of engineering geological documentation was done on such sections. Geophysical methods like geoelectric mapping and gravimetry methods were applied to detect possible caverns ahead of excavation. In sections with a large number of caverns, correction of the tunnel route is not acceptable because the surrounding rocky mass is also extremely karstified. In these particular cases, the cavernous zone is overcome by the classic excavation method in front of TBM head. All small caverns are filled with concrete to the elevation of the invert. More significant caverns that slowed down the progress of the TBM are registered on the next chainages:

– – – – – – – – –

4 + 174 to 4 + 177, empty cavern 4 + 238 to 4 + 284, cavern full of clay (manual excavation) 5 + 371 to 5 + 378 7 + 378.5 to 7 + 429.5 10 + 639 to 10 + 653, rehabilitation caverns above TBM heads (Fig. 4.65) 10 + 732 to 10 + 761 (Fig. 4.66) 11 + 400 to 11 + 413 (Fig. 4.67) 11 + 495 to 11 + 570, a cavernous zone with a length of over 70 m (Fig. 4.68). 11+ 607.7, cavern with a big empty space above and with clay beneath the tunnel invert (Fig. 4.79)

When encountering a cavern in calota that is filled with blocks and clay, there is systematic support above, on the way to unloading the machine head. When there is a large overburden above the cavern, and using the borehole from the surface is too complicated, then filling of the empty space in front of the machine head, as well as above calota was done from the tunnel, as shown in Fig. 4.66. Space in front of the TBM head is filled with inert material—sand—and then part of the cave above is filled with concrete in multiple stages. An empty cavern under the tunnel, about 13 m long, is bridged with a massive concrete slab in which an aerationdrainage (and inspection) shaft was left (Fig. 4.67). Upon arrival in the cavernous zone between chainages 11 + 495 and 11 + 570 (Fig. 4.68), there is the considered possibility of performance deviations. Supplementary geophysical research and reinterpretation engineering of geological data was done and it was concluded that deviation does not promise better rock conditions for the TBM. It was decided to pass this section by application of a classic excavation method in front of the TBM head. This solution involved pulling the TBM back to the point of connection

4.5 Tunnels

243

Fig. 4.59 Caverns in tunnel for Konavosko Polje dewatering 1. Dolomites 2. Cavern deposit (clay, sand and limestone blocks) 3. Concrete lining 4. Level of cavern deposits before excavation (Roglić & Baučić, 1958)

244

4 Water Resources Projects

Fig. 4.60 Flood during excavation of access tunnel for underground machine hall of Power Plant Dubrovnik (photographer unknown)

with the access tunnel, for simpler applications of classic excavation technology. Depending on the characteristics of different caverns, different solutions of rehabilitation were applied. Conquering the largest cavern in this zone, 10 m long (11 + 540 to 11 + 550), is shown in Fig. 4.69. Filling caverns with concrete up to the invert was chosen as the most acceptable in this case. A special problem was overcoming the cavern at chainage 11 + 607.7 (Fig. 4.70). The cavern was filled with clay and blocks up to the height of the tunnel calot, and above was a large empty space. Trying to go directly with the TBM through the clay did not succeed; the front part sinks due to the weight of the TBM head. Because of this, movement ahead is stopped. After detailed geological and speleological inspection and drilling of exploratory boreholes below the

level of the tunnel and laterally, a solution was accepted, whose implementation required 70 days. One of the benefits in this case was small overburden, and filling was executed through the large diameter of a borehole with surface terrain. Figures 4.70 Overcoming the cavern at chainage 11 + 607,7 using the borehole from surface (a) Cross-section along the tunnel trace (b) Cross-section perpendicular to the tunnel trace (c) Layout (horizontal cross section) Explanation numbers are in the text, together with an explanation of working phases. The procedure was carried out in 11 working phases: 1. Drilling 4 boreholes under TBM heads (5 days) 2. Drilling and borehole casing ∅ 148 from the surface terrain (16 days)

4.5 Tunnels

Fig. 4.61 Karst channel at the route of tail race tunnel II 1. Triassic dolomites 2. Cross-sections of karst channel at different chainages 3. Contour of tail race tunnel 4. Water level in the karst channel

245

5. Chainages in tunnel 6. Dip-strike of fault along which the channel was developed (Gašparović, 1979)

Fig. 4.62 Head race tunnel of HPP Dubrovnik

3. Dismantling concrete blocks at invert and withdrawal of TBM (4 days) 4. Excavation bypass adit and TBM returning heads in profile undermine (6 days) 5. Production of wooden partition wall for aggregate (4 days) 6. Cavern filling with aggregate through the borehole from surface (7 days) 7. Concreting protective calot through the borehole from surface (1 day)

8. Removal of wooden partition wall (1 day) 9. Excavation of aggregates and natural filling of the caverns, with its export (17 days) 10. Concreting the invert and the side through the cavern (6 days) 11. Filling bypass adit with concrete (3 days) The measured water levels in the investigation boreholes showed that, in a dry period, the level of underground water is below the level of the tunnel but, in a period of flooding in

246

4 Water Resources Projects

Fig. 4.63 Outlet of Fatnica—Bileća tunnel. Place of future HPP Bileća. (Photos Milanović)

Fatničko Polje and simultaneously heavy rainfall, the groundwater level rises above the level of the tunnel. In this time, floods in the tunnel are very likely. In the case of evenly deployed precipitation, the levels in boreholes situated at the rim of Fatničko Polje are close to the flood level. GWL measurements in borehole PB-1 showed that the tunnel is also in danger from the waters that sink into Gatačko Polje and flow directly towards Trebišnjica springs (Fig. 4.71 and 4.72). This borehole is 3.5 km from the tunnel route toward the east (Plana village area). Notice the groundwater level in F-3 is the same as the water level in Fatničko Polje. It is evident from the diagram in Fig. 4.72 that there are frequent cases in which the groundwater level in the area of PB-1 is higher than the flood in Fatničko Polje and the tunnel level. In Fig. 4.72, those cases are marked with B. This means that in this period the tunnel is threatened, above all, by the waters flowing from the direction of Gatačko Polje. This is confirmed in the flow excavation tunnel. According to the observations of V. Jokanović, flooding of Fatničko Polje also means flooding of the Pađeni section and inflow of water into the Podtuhor section. In the flooded tunnel section Podtuhor,

underground flows of Gatačko Polje—Trebišnjica springs have a larger influence than the waters that sink into Pasmica Ponor in Fatničko Polje. Inflows into the tunnel were registered even when there was no water in the polje, but levels in PB-1 were higher than the tunnel levels. It is characteristic that, in the wet season, each more intense rainfall (over 50 mm) causes an increase in the level of underground water in the upstream part of the tunnel. This precipitation does not threaten the downstream section. During excavation of the upstream section, the tunnel was flooded about 120 days every year. Measurements carried out in December 2018 determined that the seepage along unlined Fatnica—Bileća tunnel is about 40 m3/s (oral information, D. Vujović).

4.5.5

Dabar - Fatnica Tunnel

The purpose of this tunnel, with a length of 3.24 km, is water transfer from Dabarsko to Fatničko Polje. This tunnel transfers part of the water from the Bregava River catchment area into the Trebišnjica River catchment area. Under

4.5 Tunnels

247

Fig. 4.64 Tunnel Fatnica Polje—Bileća Reservoir, simplified cross—section and layout (Milanović, 2006)

operational conditions, the first phase of the Hydrosystem Trebišnjica water transfer is possible only at certain water levels in both poljes. The tunnel passes through a highly karstified limestone ridge that separates these two poljes (Fig. 1.60). Some of the deeper shafts in this area are located here (Zvonuša and Tumorovača). A relatively small overburden (about 140 m) with numerous sinkholes, shafts and faults on the surface indicated the the possible presence of a number of caverns along the route of the tunnel. This was confirmed by the results of geoelectric investigations. On the basis of detailed geological mapping of the terrain surface, a geological cross-

section along the tunnel route was constructed, which was confirmed during excavation (Bašagić et al., 1987). One part of the prognostic profile is displayed in Fig. 4.73. During excavation, a large number of caverns were registered, most of which were filled with clay material. The largest cavern has been speleologically explored. On the left side, it follows the axis of the tunnel for approximately 100 m (Fig. 4.74). The bottom of the cavern is covered with limestone blocks and extremely clean plastic clay, with a thickness up to a couple of meters. Even it was designed to be without lining, due to the numerous caverns, construction of concrete supports in a

248

Fig. 4.65 Remediation of cavern above the TBM head (10 + 639–10 + 653). 1. Cavern 2. Karstified limestone 3. Steel arch support 4. Timbers 5. Concrete

4 Water Resources Projects

Fig. 4.67 Remediation of cavern at chainage 11 + 400 to 11 + 413 1. Cavern 2. Concrete weak 3. Shaft for aeration and drainage 4. First stage of excavation 5. Second stage of excavation

number of places along the tunnel could not be avoided. The lining structure for every specific place is statically computed and adapted to the characteristics of the cavern, i.e., karstified zones. In the example shown in Fig. 4.75, part of the tunnel is in solid rock, and part rests on a clayey cave deposit. There was, therefore, the possibility for loss of support and rotation of tunnel structures. The solution consisted of bridging the clay zone with reinforcement concrete and a sufficient number of supports that pass through clay to the solid rocks.

4.5.6

Fig. 4.66 Remediation of cavern from the tunnel (10 + 732–10 + 761). 1. Clayey deposits 2. Sand 3. Support 4. Shaft 5. Pipes connected with concrete pump 6, 7, 8. Concreting phases

Tunnel for RPP Čapljina

The head race tunnel between the Hutovo regulatory pool and the reversible RPP Čapljina is 8.093 km long, with a diameter of 8.0 m. On the route of the tunnel, at chainage 3 + 637 m, there is a cavern of large dimensions, with an approximate volume of 150,000 m3. The length of the cavern along the axis of the tunnel is about 60 m, with an average width of 25 m to 30 m. The height of the cavern is about 85 m. The cavern was created in the core of the anticline structure, which is built of carbonate sediments of the Turonian age, and is high above the maximum level of underground water (Fig. 4.76). After speleological investigations of the spatial position of the cavern, a decision was made to carry out the deviation of

4.5 Tunnels

249

Fig. 4.68 Simplified geological cross-section of the tunnel with cavernous zones

Fig. 4.69 Overcoming the problem of an empty cavern at chainage 11 + 540–11 + 550

the tunnel, at a length of 170 m (Fig. 4.77). From the entrance to the cavern (about 3.5 km), the tunnel passes through compact limestone without any sign of karstification. In the section closer to Svitava, just before the surge tank (with overburden of 80–50 m), the tunnel passes through a large cavern filled with clay, sand and limestone blocks. The cavern was formed along a subvertical tectonic zone, with a north—south direction in the area of erosion contact Cretaceous and Eocene limestone. The mentioned tectonic zone, which slightly deviates from the direction of the tunnel extension, intersects several secondary crack systems. Such a fracture system enabled intensive karstification and the formation of a large cavern. The tunnel lining is significantly reinforced there and supported on limestone, which was supposed to be part of the bedrock. Later, it turned out that they were big blocks that float in clay-sand material. Soon after the tunnel was operational (1979),) cloudy/muddy water appeared in the Svitava rim springs (a distance of about 1300 m from the place of the defect). Simultaneously, collapse was created at the surface. In samples from the springs, content of suspended clayey material reached 20%. Losses in the tunnel increased from 50 l/s to around 1000 l/s. With a number of simultaneous measurements, it was determined that the losses depend on piezometer pressure, which significantly differentiates from static water level, and they were + 13 m in pumping regime and - 13 in turbine operation of the power plant. It was established through investigation that the tunnel pipe was missing support at 16 m due to the washing and settling of clayey material, and a large empty space was created, about 7 m wide and 8 to 15 m deep (Fig. 4.78).

250

4 Water Resources Projects

Fig. 4.70 Rehabilitation of the cavern at station 11 + 607,7 (a) Profile along the tunnel route (b) Administrative profile on the tunnel route (c) Plan

The blocks which supported the tunnel construction sunk, together with clay. Flushing and settling of the material caused the formation to collapse on the surface and created a breach in the calot lining (Fig. 4.79). Through the access opening in the tunnel invert, 70 × 70 cm (Fig. 4.79b), was possible the entrance and

speleological investigation and mapping the cavernose space below tunnel. This entire zone was investigated, with numerous boreholes, smoke tracers, Na-fluorescein and TV logging. The contours of the cavern below and above the tunnel were defined (Fig. 4.80).

4.5 Tunnels

251

Fig. 4.71 Correlation of the water level fluctuation graph in PB-1, F-3 and PL-1 and Trebišnjica spring hydrograph 1. Precipitation 2. Spring discharge 3. Groundwater level 4. Level of Bileća Reservoir

252

4 Water Resources Projects

Fig. 4.72 Typical position of piezometric lines between PB-1 and F-5

Through investigative drilling, it was established that a part of the tunnel tube, with the entire perimeter, is situated in clayey-sandy material. The characteristics of that zone were defined through investigation drilling from the surface (Fig. 4.80) and from the tunnel (Fig. 4.81). Based on the collected data, rehabilitation works consisted of two reinforced concrete plates (horizontal and arched) that are founded and anchored in compact cavern walls. The interspace between and above the slabs is filled with prepacked concrete, and the empty space in the sides is filled with grout mix (Figs. 4.81 and 4.82). The empty space above the tunnel pipe is not filled.

Cavern filling was started by injecting aggregates through borehole B-12. Control filling is performed with a TV camera for boreholes. It was concluded that it is not possible to achieve the desired result in this manner, so remediation started inside the cavern under the tunnel (Milanović, 1987).

4.5.7

Tail Race Tunnel of RPP Čapljina

The tail race tunnel of RPP Čapljina is located entirely below groundwater level, in karstified Eocene limestone. The entire length of the tunnel is situated in permanently saturated karstified Eocene limestone. The length of the tunnel is

4.5 Tunnels

253

wide fractured and karstified zone

potential subsidence areas at surface

140 m

karstified limestone

caverns filled with clay-sandy deposits

1+250

1+300

potential subsidences areas in the tunnel

1+350

1+400

1+450

1+500 m

Fig. 4.73 Possible weak zones in part of the Dabar—Fatnica tunnel route. (Bašagić et al., 1987)

631 m and the diameter of the excavation is 10 m. The elevation of the tunnel invert changes between levels— 25 m a.s.l. and—14 m a.s.l. During the excavation, at chainage 0 + 440.70, a karst channel was cut, from which the water burst into tunnel. Water with pressure of 2,2 bars very quickly submerged the tunnel. Inflow into the tunnel was about 300 l/s. Divers established water breakouts from the caverns of 40 × 70 cm (Fig. 4.83). A cavern is formed in the cracks whose presence is registered by geological mapping of the access tunnel to the

Fig. 4.74 Cavern at left side of Dabar Polje—Fatnica Polje tunnel (layout)

underground power plant hall. Hydrogeological analysis established the connection of this cavernous zone with the springs of the Svitava perimeter. An attempt by divers to close the cavern was unsuccessful. On that occasion, deadly are suffered three divers: Božo Pljetak, after 1 month of underwater works, and Krešo Stanković and Ervin Priskić subsequently, during the first dive into a submerged tunnel. For this reason, solving the problem using divers was abandoned. Instead, the problem was addressed by means of large diameter boreholes, which were drilled from the gallery excavated from the access tunnel, at an altitude of 8.35 m (Stojić et al., 1976). A fan borehole entered the front of the tunnel section with a cavern (Fig. 4.83). An aggregate fraction of 7–16 mm was inserted through the boreholes closer to the tunel head. Over the other row of boreholes, an aggregate fraction of 0–16 mm was used as a sufficiently impervious protective embankment, which was supposed to prevent the loss of grouting mix towards the submerged part of the tunnel. After that was grouted karstified zone that, for the beginning of the excavation, pumped out water from the tunnel. Further progress of the excavation required local pre-grouting of rocky masses in front of the tunnel head.

254

4 Water Resources Projects

Fig. 4.75 Dabar—Fatnica Tunnel. Cross-section perpendicular to the tunnel and cavern filled with clayey sediments 1. Cavern 2. Clayey sediments 3. Karstified limestone 4. Reinforced concrete

4.5.8

Burst of Underground Water during Excavation of Power Plant Hall of RPP Čapljina

In the course of excavation of the underground structures for RPP Čapljina, in karstified Eocene limestone, at a depth of 34 m, i.e., about 40 m below sea level underground water, a karst channel was cut, through which water discharges under pressure, about 100 l/s. Further excavation was completely stopped. Water discharge is stopped in the following way: Through channels with water inflow, there is a metal “tapping bell” with a drainage pipe, through which the water flows to a special shaft and is pumped to the surface (Fig. 4.84). The end of the pipe is equipped with a valve. A special (grouting) tube is connected to drainage pipe, which is also equipped with a valve. After that, the entire floor of the room is covered with a concrete slab, 2 m thick. Due to strong uplift, the slab is anchored to the limestone substrate. By closing the valve on the exit pipes, water circulation in the karst channel is stopped. In calm water conditions, the channel was grouted through the grouting tube and “tapping bell”. After grouting, the concrete slab was removed by blasting, and excavation at an elevation of—34 m continued.

According to the preliminary design, HPP Dabar would be located underground. In the first phase, extensive works were carried out in the wider area of Vrijeka (location of the power plant) and complex investigation works were executed. Eleven exploratory boreholes were drilled from the surface of the polje: DB-1 and DB- 2 as well as 9 boreholes with SD marks, with a depth of 27 up to 157 m (Fig. 4.85a). An exploratory adit (gallery), with a length of 536 m with four galleries was made in the planned area of the underground power plant hall. The size of the galleries is 2 × 38 and 2 × 10 m. Total length of the underground works is 662 m. Eight exploratory boreholes (DS-1 to DS-8) had depths from 35 to 40 m. Figure 4.84b shows the arrangement of the boreholes in the area of the planned underground power plant. Geoelectrical surveys were carried out, with surface terrain and seismic and geoelectric cross-hole examinations, from a borehole underground. The exploratory excavation for PP Dabar goes deep into the hinterland of the Vrijeka Spring, so it was expected to have problems with underground water in rainy periods. In several places, empty caverns of smaller dimensions or caverns filled with sand have been cut by the gallery. This is why, during excavation of this tunnel, all cavernous zones were protected with concrete lining. Despite that however, there was water breakthrough several times during excavation. It happened for the first time on December 31, 1985, and the discharge lasted until the end of February 1986 (Fig. 4.86). The largest amount of water that flowed from the investigation adit was evaluated at 5 m3/s. Next to outflow from adit, the Vrijeka Spring and Opačica torrent flow were active, and the larger part of the polje flooded. Figure 4.86 A shows flow from the excavation on February 20, 1986. At the same time, the larger part of the polje flooded (Fig. 4.87b). Water burst out from the caverns in the central part of the excavated gallery (Photo in Fig. 1.12), so that galleries in underground mechanical halls were not submerged. Because of risks caused by problems with underground water, the designer decided to place the machine hall on the surface. There, the problem of microlocation appeared, due to the position of the reverse fault and foundation problems but also due to eventual seismic activity of this fault. It was decided that the machine hall should be partially buried in the carbonate environment north of tectonic contact.

4.5.10 Lazarići Tunnel 4.5.9

Investigation Adit for HPP Dabar

Design documentation for HPP Dabar from 1962–1991 was done by Energoinvest, Sarajevo. The location of the power plant changed many times for different reasons, including hydrogeological and geotechnical problems.

The Klinje—Lazarići tunnel has a length of 2920 m and transports water to the TPP Gacko. The axis of this tunnel is located at an altitude of about 1000 m above sea level. The entrance portal of the tunnel is located at an altitude of 1009 m, and the exit is at an altitude of 982.12 m. The

4.5 Tunnels

255

Fig. 4.76 Cavern on the route of the head race tunnel for reversible RPP Čapljina 1. Tunnel 2. Anticlines axis 3. Fault 4. Geological boundary 5. Shaft

cross-sectional area is 4 m2. Water is transported through steel pipes with a diameter of 1000 mm in the tunnel and 500 mm outside the tunnel. The length of the pipeline outside the tunnel is 3229 m. In the area of the entrance portal, the tunnel passes through Paleogene sediments; in the central part, through the Cretaceous limestone; and in the area of the exit portal, through Jurassic limestone.

4.5.11 Head Race Tunnel for HPP Dabar The length of the head race tunnel for HPP Dabar, from the intake structure in Nevesinjsko Polje to the hydroelectric

power plant in Dabarsko Polje, is 12,125 m, with a diameter of 5.2 m. The final profile of the tunnel, after lining, is horseshoe-shaped, with a diameter of 4.6 m. Tunnel excavation was completed in June 2020, Initially, a part of the tunnel is in the conglomerates Promina formation, the longest part of it in karstified Cretaceous limestone. Comparing with other tunnels in karst, the inflows of water during and after excavation are negligible. In the rainy period from December 2020–February 2021, inflows into the tunnel were between 100 and 150 l/s. One of the highest flows of Q = 123 l/s was measured on January 02. 2021 at the junction of the basic and access tunnel, Straževica entrance (Fig. 4.87).

256

4 Water Resources Projects

4.6

Fig. 4.77 Deviation of tunnel due to cavern at tunnel route 1. Cavern 2. Karsified limestone 3. Fault 4. Concrete plug 5. Deviation of tunnel (Božičević & Milanović, 1982)

Remediation of Trebišnjica Riverbed

In the dry period, in natural conditions, the Trebišnjica River dries up downstreamfrom the Trebinje, near Dražin do. For 65 km, the riverbed is dry and the levels of groundwater are deep below the bed. Basic hydrological and hydrogeological properties of the riverbed are presented in Sect. 2.1.11, Characteristics of the river flow of Trebišnjica through Popovo Polje. In order to achieve watertightness of the Trebišnjica riverbed and make possible the transport of water from the Gorica Dam to the Hutovo regulatory pool, it was necessary to prevent large losses along the riverbed, through numerous ponors and ponor zones. In the dry season, these amount to 63.4 m3/s. The choice of a technical solution depended on knowledge of an exceptionally complex regime of surface and groundwater (Fig. 4.88). Figure 4.88 (A, B, C) shows a simplified model of the water regime of Popovo Polje after construction of the Gorica Dam, with three key hydrological and hydrogeological situations: A and B—before regulation of the Trebišnjica riverbed and the construction of the RPP Čapljina. C– after the construction of RPP Čapljina. A—Flow regime in the dry period after construction of the Gorica Dam, under conditions which, due to the obligation to discharge 3 m3/s, were close to the regime under natural conditions. The flow of Trebišnjica exists approximately up to Dražin do. The sketch shows the position of

Fig. 4.78 Cavern cross-section around and beneath the tunnel tube 1. Shaft in concrete lining 2. Reinforced concrete lining 3. Damaged lining 4. Screen wall 5. Empty cavernous space 6. Cave deposits 7. Empty space above the tunnel lining 8. Borehole investigation 9. Limestone

4.6 Remediation of Trebišnjica Riverbed

257

Fig. 4.79 (a) Cavern beneath the tunnel lining (b) Access shaft in reinforced tunnel lining (c) Cross-section perpendicular to the tunnel axis 1. Tunnel lining 2. Part of lining additionally reinforced 3. Collapse at surface 4. Cave origin as a consequence of collapsing 5. Empty

cavernous space below the tunnel tube 6. Cave deposits (clay, sand and limestone blocks) 7. Limestone 8. Boreholes 9. Fault (Milanović et al., 1987, Photo Božićević)

eight profiles for simultaneous measurment losses along the bed. This is the period when there is no connection with the Neretva catchment.

B—Flow in natural conditions, wet period, when Trebišnjica flows along its entire length. Then, all springs, all estavelles and all ponors are active, but not constantly

258

Fig. 4.80 Cavern contours at damaged section (layout) 1. Tunnel 2. Collapse 3. Cave 4. Shaft cut through the lining of the invert arch 5. Limestone 6. Cavern contour line below the tunnel tube 7. Cavern contour line above the tunnel tube 8. Connection established by smoke tracer (Milanović et al., 1987)

and not with the same intensity. The waters of numerous springs flow into Trebišnjica. A part of this water sinks and flows toward the lower erosion bases (Dubrovonik Littoral and Neretva valley). A large part of the water from the catchment area north of Popovo Polje flows below the polje, directly towards the sea, and it discharges there through numerous springs and submarine springs, so to quantify its quantity is difficult. C—After regulations, the Trebišnjica riverbed flows into the canal (paved by shotcrete). Losses along the bed are minimized and a constant flow is established along the bed (canal) through Popovo Polje. Certain amounts of underground water continue to flow under the bed towards the south, and the estavelles work mostly in the regime of springs. Watertightness of the riverbed, including the banks of the Hutovo regulatory pool, is achieved by construction of a watertight blanket of shotcrete, 5 cm thick, and a total surface area of 2.2 million m2. In the previously performed experiments, with linings made of asphalt-concrete, shotcrete with reinforcement, shotcrete without reinforcement, and cement, cement-lime and bituminous soil stabilization, the

4 Water Resources Projects

best results for lining have shotcrete, with a thickness of 5 cm, with wire-mesh reinforcement of Ø 3.1 mm, and openings of 10 × 10 cm (Fig. 4.89). The adopted final canal shape is a trapezoidal canal with a depth of 2.2 m to 9.0 m at the very end (downstream from Crnulja Ponor). Since there was a real danger of uplift pressure along the Trebišnjica, 16 piezometric profiles were established, whose characteristics are presented in Sect. 2.1.11. Appearances of strong uplift were registered on a total length of 3.5 km (Paviša & Mucović, 1979). Drainage valves were installed in those zones. During construction of the embankment along the expanded section of the riverbed downstream from the Crnulja Ponor, recent collapses of the already constructed embankment body were registered (Fig. 4.90a). This forewarned of the possibility of similar appearances during the operation of the structure. Immediately after power plant began to operate, losses were measured along the canal (67 km and flow 45 m3/s) of 2.8 m3/s and seepage of 2.2 m3/s in the Hutovo Reservoir. For flows between 18 and 20 m3/s, losses in the canal were significantly smaller, about 1.0 m3/s. During canal operation, fractures in the shotcrete were registered in several places, both in the sides of the basin and in the sides of the embankment along the canal (Fig. 4.90b). These places were rehabilitated by installing drainage pipes. Damage to the linings were also registered in the canyon part of Trebišnjica, mainly due to strong uplift. Some places were demolished, due to strong uplift, and about 100 square meters of lining separated and were transported downstream. Figure 4.91 shows a panoramic view of the lined Trebišnjica riverbed downstream from Ravno. Traces of the former flood level are still visible on the slope. After rehabilitation, losses were reduced to 1–2 m3/ s (Trebišnjica canal + regulatory pool), depending on flow amounts in the canal and water level in the pool. The collapsing sinkholes still occur tempoararily, especially at the bottom of the canal, where the thickness of alluvial sediments is up to 10 m (1998, 2002, 2003). At the end of July 2001, 3928 m3/s was discharged from the Gorica Dam, and the flows were measured at selected profiles (Fig. 4.92). In September 2003, lining damage in the canal was registered, from Ravno to the Klek tunnel but also several larger collapses—sinkholes. The location of one of them is approx 500 m upstream from the Klek tunnel. This collapse was repaired before, but now the dimensions are much larger (approximately 40 m3). The collapse is located approximately in the same area as the embankment accident that occurred during canal construction (Fig. 4.90a).

4.7 Drainage of Mokro and Petrovo Polje

259

Fig. 4.81 Tunnel section in clayey-sandy sediments 1. Tunnel lining 2. Empty space 3. Clayeysandy deposit 4. Aggregate-filled cavern through borehole B-12 5. Fractured limestone 6. Solid limestone

?

B-12

2

B-13

B-14

4

?

38° 30°

5

68°

1

2

3 2 6

0

2

Losses along the riverbed include water tapping for various local purposes, first of all for agricultural purposes but also for water supply. Along with damage and accidents is degradation of shotcrete after 40 years of exposure to water flow (Fig. 4.93). The probable cause for this kind of damage is non-compliant prescribed recipes and technology during shotcrete installation.

4.7

Drainage of Mokro and Petrovo Polje

Section 1.6.3 presents natural characteristics of the Mokro Polje, in which floods are a regular annual phenomenon. Since Mokro Polje (268–269.5 m above sea level) is some meters lower than Petrovo Polje (271–273 m above sea level) and is inclined towards the east, their flood regimes are different. While the natural drainage of Mokro Polje takes place exclusively underground via numerous estavelles, a

4

6

8

10m

?

large part of Petrovo Polje water is drained through canals (Fig. 4.94) toward the Trebišnjica River. A smaller part of the water infiltrates through the very permeable fluvioglacial sediment and flows away, through the underground, toward the springs on the seacoast. Construction of the pipeline (on the surface of the Gorica—Plat tunnel) formed a physical surface barrier between these poljes. The purpose of siphonic culverts under the pipeline (made during construction of the tunnel, along with an additional siphon in 1986) is the drainage of floodwaters of Mokro Polje. The main drainage canal is to the Trebišnjica riverbed, however, because the siphonic culvert can only transport flood peaks because of unfavourable level conditions. Several secondary canals flow into the main drainage canal, among which is the most significant canal that drains surface water between Aleksina Međa and Volujac. During reparation works along the canal, a large number of ponors/estavelles are registered. Concrete cylinders are built into them, which reduce uplift and enable underground water discharge into the canal and

260

4 Water Resources Projects

Floods in Mokro Polje represent a significant limitation for agriculture activities, and their drainage is necessary and urgent.

4.8

Plugging Karst Springs

It is not possible for a significant portion of water in karst to be tapped by dam construction and accumulation on terrain surface. The specificity of the hydrogeology of karst makes it possible, in certain cases, to form underground accumulation, for better water resources management. Construction of underground dams and reservoirs are relatively new endeavors in the field of engineering karstology. Successful underground reservoirs have been constructed in the karst of China from the middle of the twentieth century. In East Herzegovina two experiments, with plugging karst channels, were done (Obod and Jedreš). Particularly chalangging is the project of the underground PP Ombla, near Dubrovnik, with dimensions of the structures being the biggest in the world, if the project is realized.

4.8.1

Fig. 4.82 Repair work of endangered section of tunnel 1. Tunnel lining 2. Pipe for aggregate transport from surface 3. Flexible pipes 4. Grouting pipes 5. Boreholes through the lining 6. Grouting boreholes 7. Investigation boreholes 8. Anchors 9. Plastic foil 10. Pipe for drainage 11. Aggregates 12. Filter layer 13. Reinforced construction 14. Pre-packaged concrete 15. Space filled by grouting mix 16. Limestone (Milanović et al., 1987)

prevent sinking. In the Pridvorački river branch (with permanent flow), these structures operate successfully, but in the main drainage canal (with temporary and short-duration flow) there have been many accidents. Locally installed one-way valves, so-called “frog lids”, aim to enable smooth inflow and disable water seepage from the canal (Fig. 4.95).

Plugging of Obod Spring in Fatničko Polje

This spring (estavelle) is located on the rim of Fatničko Polje, on the tectonic contact (reverse fault) of Eocene flysch and Upper Cretaceous limestone. Activity of the Obod Spring in the regime of ponors is practically negligible, both in terms of time and the amount of water that sinks there, particularly after the Fatnica—Bileća tunnel become operational. So, it is not a mistake if it is classified as a temporary spring. The basic information about Obod is given in the chapters about Fatničko Polje and speleological research (1.67) and in Figs. 1.62, 1.63, 1.65 and 3.16. Karst water that flows through this spring zone belongs to the regional Trebišnjica aquifer, which overflows into Fatničko Polje. It functions as natural retention in the period when the polje comes under upward pressure because the downstream channels do not have enough capacity to drain all the water towards the springs of Trebišnjica. This is a period when under the strong southern slope of the field will also be uplifted, and then the ponor zone of Pasmica will work in the regime of springs. After speleological research in 1964, a decision was made about the experimental sealing of the exit channel of the Obod Spring. At the exit part of the channel, a massive concrete plug was constructed (Fig. 4.96a, b and c). The plug is 10 m high, with an average width of 3.5 m (Petrović, 1965). The main purpose of this experiment was to

4.8 Plugging Karst Springs

261

Fig. 4.83 Closing of groundwater intrusion into the tailrace tunnel of RPP Čapljina 1. Boreholes 2. Flooded tunnel 3. Water intrusion 4. Karst channel 5. Cement mortar 6. Prepacted concrete 7. Grouted (Stojić et al., 1976)

investigate the possibility of preventing the floods of Fatničko Polje, i.e., that all water is forced to flow exclusively underground towards the Trebišnjica springs. The plug was calculated on a pressure of 40 bars. The pressure behind the plug is controlled across pipes embedded through the plug, which is extended above maximum flood level and equipped with a pressure gauge (manometer).

However, the first rainfall after construction of the plug was extreme. On October, 1965 over 100 mm of rain was registered, on average, in the catchment area. At some precipitation stations, 230 mm/24 h was registered. The Ključki Ponor (level 818 m) in Cerničko Polje and Obod (level 476 m) are connected by a direct channel system and very quickly come under pressure. During the night between October 11 and 12, 1965 dozens of new springs

262

Fig. 4.84 Tapping procedures of water intrusion during excavation of RPP, the deepest part of the machinehall 1. Karstified limestone 2. Karst channel with water under pressure 3. Flow direction 4. Metal tapping bell 5. Provisional clayey waterproof belt 6. Anchor 7. Concrete slab 8. Direction of grouting mix penetration. 9. Pipe with valve at the end

appeared on the slope, 80–100 m above the plug level. (Fig. 4.95d). Total discharge of these springs was about 11 m3/s. The pressure in the karst channel rose from 7.0 bar that morning to 9.25 at 18:00 h to 10.6 bars the next day. Flow on the Baba Jama temporary spring grew to 5 m3/s. This condition in the karst outcrop caused strong local earthquakes in the Obod area, with trembling soil and sliding terrain. Explosions of captured air “pillows” in karst channels caused local, but intense, induced seismicity. The road above Obod settled 50 cm for a length of 30 m, and houses on the slopes were damaged. Instead of the program lasting one hydrological year, this experiment was suspended. The

Fig. 4.85 (a) HPP Dabar. Investigation gallery for underground power plant (b) Investigation works (adits and boreholes) at place of underground power plant

4 Water Resources Projects

reinforced concrete plate at the top of plug, dimensions 1.53 × 1.40 m, was blasted. At that part of the plug, 10 kg of explosives were pre-installed. Immediately after blasting, and discharge of a huge amount of water, the pressure suddenly fell, and hypsometrically the highest springs dried up after one hour. During the following 3–6 h, discharge stopped on all newly formed springs. The size of the opening in a concrete plug is not enough large for discharge of water under natural conditions. Because of this, in extreme cases, retardation of part of the water occurs in the channel behind the plug and there is the appearance of springs on the vertical cliff above Obod. A possible consequence can be violation of slope stability and endangerment of structures (the road and buildings). This is why it is necessary to widen the exit opening, with the possibility of passing multiple larger amounts of water than currently exists. These results show that a part of the karst aquifer (between Cerničko and Fatničko Polje) has very good water conductivity, that is, transmissibility of karst channels is huge, but retardation capabilities are very poor. Also, the experiment indicated some unforeseen negative effects that artificial accumulation in underground karst can cause. Plugging the karst channel just on exit turned out to be problematic; it means bringing piezometric lines on the surface above and around the output opening.

4.8.2

Plugging of Jedreš Spring in Nevesinjsko Polje

Jedreš Spring is situated in Eocene conglomerates on the periphery of the Nevesinje urban area, at an altitude of 904 m, and was tapped for the city’s water supply (Fig. 4.97a). The channel of Jedreš is the base flow of a karst aquifer, created in conglomerates. Discharge varies between 1.0 and 350 l/s. To investigate the possibility of storage and regulated discharge by sealing the spring channel, necessary investigative works were performed: hydrological measurements, geological prospecting, investigative drilling and speleological research. From the four investigative boreholes, two entered into the karst channel (Fig. 4.97b). Through speleological research, it was established that enough cavernous space exists in the spring for accumulation of amounts of water that could mitigate the deficit of water supply for Nevesinje during the dry period of the year. The channel is plugged 60 m upstream from the spring outlet. Until this place, there is an access adit, and there the channel widens due to the foundation of the plug. The concrete plug was built in the upstream part thatextends (Figs. 4.98 and 4.99).

4.8 Plugging Karst Springs

263

Fig. 4.86 Dabarsko Polje (a) Portal of investigation adit at area of PP Dabar (b) Flood of Dabarsko Polje, February 20, 1986 (Photos Milanović)

Fig. 4.87 Nevesinjsko Polje—Dabarsko Polje Tunnel (for Power Plant Dabar) (a) Outflow from tunnel (b) Outflow from tunnel above flooded Dabarsko Polje (Photos Jokanović, 2021)

The diameter of the plug is 3 m, and the thickness is 1.5 m. The rock mass around the plug is grouted. In the plug, four steel pipes are embedded: one with the role of bottom outlet; two in the middle with the role of water intake, and the fourth at the top, with a large diameter, for inspection of underground reservoir space (Fig. 4.100).

After several experimental fillings, it was determined that the underground reservoir level of the water must not exceed 12 m. It was also established that the underground space for this level of the reservoir is watertight. To avoid costs for construction of an overflow structure, the bottom outlet was calculated for maximum flow of Jedreš Spring and should

264

4 Water Resources Projects

Fig. 4.88 Schematic presentation of water regime in the area of Trebinjsko-MokroPopovo Polje 1. Ponor 2. Estavelle 3. Karst spring 4. Temporary surface flow 5. Underground flow 6. Underground flow beneath the polje floor 7. Overflow at Gorica Dam

serve for the evacuation of large waters (role of overflow) at the same time. In this way, it was left to the human factor to decide on and manipulate the release of excess water. Obviously, this was wrong, because the human factor is the weakest point in the operation. Collapse occurred because of inadequate manipulation in a period of intense precipitation (valve on the bottom outlet was not opened), and the water level grew above the permitted level. This situation caused collapse of the terrain above the caves, i.e., above the storage space (Fig. 4.101).

4.9

Underground Dam and Ombla Reservoir

4.9.1

Development of an Idea

In 1969 the watertightness problem of the Trebišnjica riverbed was discussed. The idea for construction of a grout curtain in the hinterland of Ombla was suggested, to increase the groundwater levels in the area of Popovo Polje and, in this way, to prevent sinking from the riverbed. Extensive research

4.9 Underground Dam and Ombla Reservoir

265

Fig. 4.89 Trebišnjica riverbed blanketed with shotcrete, 2005 (Photo Milanović)

Fig. 4.90 Head race canal for RPP Čapljina (a) Collapse of the enbankment area during construction (Photo 1975) (b) Damage of shotcrete blanket on the bank of the head race canal during power plant operation. (Photo by Milanović, 2009)

works were carried out (1969–1971), including detailed geological mapping (J. Mladenović), detailed structural analysis and determination of catchment areas (Fig. 2.46, Milanović, 1970), geophysical research, borehole execution, tracing of underground flows and speleological research. This research established the concentration of the most important underground flow zones and karst channels, forming a narrow corridor, through which the water flows towards Ombla

Spring. This was in the area of Zaplanik, approximately 3 km into the hinterland of Ombla. Geoelectrical investigative works indicated an approximate morphology of the base of karstification and the position of a corridor, along which the rocky mass is intensely karstified (Aranđelović, 1984). Along this zone are channels of huge permeability, with concentrated flows toward the Ombla (Fig. 4.102).

266

4 Water Resources Projects

Fig. 4.91 Trebišnjica riverbed, blanketed by shotcrete—panoramic view. On the hillside, flood levels under natural conditions are visible 2009. (Photo Milanović)

Fig. 4.92 Flow along the paved Trebišnjica riverbed (July 2001)

Of particular importance was the drilling of eight exploratory/piezometric boreholes, with depths of 250 to 280 m, and the position of the corridor was confirmed on this basis. In 1952, a hydraulic gauging station was founded on the Ombla Spring, and systematic observations started in 1960. Since it was decided that watertightness of the Trebišnjica riverbed should be solved by blanketing with shotcrete, further works in the Ombla hinterland were stopped. However, further observation of groundwater level fluctuations continued in the eight mentioned piezometers. Results of all mentioned research, especially the results of observation of

piezometers, served for the preparation of the master’s thesis, “Hydrogeology of the Ombla karst aquifer” (1975) and later published work with the same title (Milanović, 1977), which initiated the possibility for utilization of Ombla water by construction of an underground dam. The second stage, which elaborates on the idea and the assessment of its reality began in 1980/81. The idea was developed by HPP Dubrovnik, that is, EP Croatia, as property owner, and the Institute for Use and Protection of Karst Water, Trebinje, which performed and coordinated additional investigative works. These works are synthesized in the

4.9 Underground Dam and Ombla Reservoir

267

The conceptual solution was made by Elektroprojekt, Zagreb and the Institute for Use and Protection of Karst Water, Trebinje. For the purposes of preparing the study and the conceptual solution, a large number of investigations were carried out: eight new boreholes in the broad area of the springs background; aerial photos of the catchment area; speleological explorations of Vilina Pećina (Fairy Cave), speleo-diving exploration of the spring channel; excavation of short adit from surface to the cave that speleo-divers discovered in the immediate vicinity; and geophysical research in the spring zone, including a deep geophysical sounding in the further hinterland. For creating the geological part of the conceptual design, more significant investigations included: Fig. 4.93 Locally damaged shotcrete after 40 years of canal operation, 2016 (Photo by Milanović)

study, “The possibility of hydropower utilization of the Ombla Spring”, Trebinje 1984. Since the study was accepted by the official owners audit committee, it followed defining the concept of the solution given in the report: “Unedrground HPP Ombla, basic geological characteristics with a solution concept”. The report was made by the Institute for Use and Protection of Karst Water—Trebinje, in 1986.

– Detailed geological mapping works of the catchment area 1:10,000 (188 km2) – Geological mapping of wider areas of Ombla and Zavrelje springs, 1:2000 – Excavation of the access gallery to 190 m and the investigation gallery to 698 m – From the surface in the wider area, 16 deep piezometric boreholes were drilled (O—borehole depths of 250–280 m), and in the immediate background of the

Fig. 4.94 Petrovo Polje, panoramic view. Position of temporary spring Oko Rasovac shaft and Zbora Spring, pipeline for HPP Dubrovnik and canals for water transfer from Mokro Polje to the Trebišnjica River

268

4 Water Resources Projects

Fig. 4.95 Protections against seepage (a) Concrete pipes in Pridvorački river branch (b) Demolished concrete cylinder in the main dewatering canal (c) One-way valve in the main dewatering canal

spring, 18 boreholes were drilled (B boreholes, depth up to 200 m). – Some deep boreholes are equipped with devices for continuous monitoring of fluctuation of GWL

Fig. 4.96 Experimental plugging of Obod Spring in Fatničko Polje (a) Cross-section with main channels and position of plug (b) Layout with position of plug and overflow at surface (c) Reinforced concrete plug 1. Body of concrete plug 2. Part of plug that can be blasted in case of emergency 3. Contours of plug 4. Anchors (d) Position of new springs at cliff (Petrović, 1965)

– From the investigation gallery, from an elevation of about +3 m above sea level, 28 boreholes were drilled, with a depth of 82 to 287 m (P boreholes). – In the area of Zavrelje spring, four boreholes were drilled

4.9 Underground Dam and Ombla Reservoir

269

Fig. 4.97 Nevesinje (a) Old tapping structure (Photo by Milanović 1980) (b) Karst channel of Jedreš Spring with piezometric borehole J-3 (Photo Božičević, 1981)

Fig. 4.98 Cave system of Jedreš Spring 1. Investigated part of channel 2. Boreholes 3. Concrete plug 4. Access addit

270

Fig. 4.99 Cross-section of enlarged part of channel with concrete plug 1. Karst channel 2. Gravel 3. Promina conglomerates 4. Enlarged part of karst channel 5. Access adit 6. Concrete parapet 7. Intake pipe

4 Water Resources Projects

8. Concrete plug 9. Inspection opening 10. Bottom outlet 11. Grouted ring around the plug 12. Underground reservoir_

Fig. 4.100 Concrete plug in karst channel of Jedreš Spring (a) after concreting (b) after assembling

– Extensive geophysical examinations were done (geoelectric mapping, geoelectrical sounding, refraction seismic profiling, seismic cross-hole, gravimetric measurements and seismic detection of noises – Radar logging and the radar cross-hole method (Niva 1990) – In the period 1989–1991, temperature measurements were made along the boreholes in the investigative gallery (Ravnik & Rajver, 1998). This research established the position of the main channels (Fig. 4.103). – A couple of local tracer examinations were organised.

– Speleologists and cave divers investigated about 3 km of karst channels. – Using the echo sounding method (Weiler & Rick, 2005), the contours of the two most significant channels (caverns) were defined. For this investigation two boreholes were drilled from the investigation gallery (Fig. 4.104). From the borehole P-122.5, scanning of caverns deep under the level of underground water was done, including 36 vertical and 46 horizontal profiles. The contoured cavern with the highest point had a depth of 112 m, and the lowest had a depth of 158 m, with a volume V = 2764 m3. From

4.9 Underground Dam and Ombla Reservoir

271

Fig. 4.101 Cross-section along part of the underground storage space 1. Maximum water boards under natural conditions 2. Maximum permitted storage level 3. Concrete plug 4. Outlet part of the karst channel 5. Storage space 6. Collapsed part of overburden

borehole PHD-2, a contoured cavern is noted, with the highest point at a depth of 36 m and the deepest at 86 m. The volume of this cavern is 574 m3.

4.9.2

Conception of Underground Dam and Reservoir

Conception of this structure is based on: – very favorable geological structure, which enables construction of underground anti-filtration facility with height up to required elevation – large amount of water that discharges from the spring – significant underground storage space in extremely karstified background – hydraulic characteristics of karst aquifer (hydraulic system under pressure)

Basic conception characteristics of the underground dam and the Ombla reservoir were presented at the scientific conference “Water and Karst” in Mostar, 1985 and at the 21st world congress of hydrogeologists held in China (Guilin, 1988). Key parameters of the underground PP Ombla are presented in publication Hrvatske vode (Paviša, 1998). Data regarding the hydrogeological and hydrological characteristics of the Ombla spring and its catchment area are given in Sect. 2.2.2, Ombla—Komolac (spring of Dubrovnik River), so they are not repeated here. In the area of the Ombla Spring itself, the flysch barrier has been eroded to sea level, so there are conditions created for the concentrated discharge of the large karst aquifer. Laterally from the spring, on both sides, the barrier rises, so that this contact on an open profile has the shape of the letter “V” with the spring at the lowest point. With such a position, flysch sediments have the role ofa dam site, which should be closed, with an underground waterproof structure built in a very karstified carbonate mass (Figs. 4.105, 4.106 and 4.107).

272

Fig. 4.102 Base of karstification with possible flow directions and position of investigation boreholes in the background of Ombla Spring (Aranđelović, 1971/1984, supplemented)

Previous research shows that with cutting (plugging) of the base flow, and secondary karst channels, the desired storage can be achieved, and in the immediate hinterland of the dam, true pressures, which are the same a few kilometers from the dam site. The horizontal distance from the spring is dictated by the maximum possible height of the underground dam and the need to be connected with impermeable rocks. Under natural conditions, the position of the lateral overflow Slavljan Spring limits the height of the dam at approximately 100 m above sea level. With additional interventions in the hinterland of that spring, it is possible to increase the level of the underground reservoir to 130 m a.s.l. Because of this height and the required thickness of the overburden, the underground dam must be situated in the rock mass at least 150–200 m upstream from the spring zone. At the same time, it must not be too deep in the mountain mass because being

4 Water Resources Projects

tight in the flysch rock mass causes difficulties. Since the karst channels with huge flow capacity on the route of the dam are at depths of 150 m below zero, it is certain that its depth locally must be at least 150–160 m, or more likely, to be completely tied to the flysch. In this way, the designed underground dam consists of a part below the elevation of 0.00 m, with a maximum depth of 280 m, and a part from an elevation of 0.00 m to the proposed dam crest, at an elevation of 135 m (Fig. 4.107). On the longitudinal schematized (simplified) cross-section (Fig. 4.106), positions of piezometer lines in various periods of natural saturation are shown, along with their relationship according to maximum reservoir level. Picture 4.108 displays a schematized transverse section of reservoir space, which shows that a rocky mass under 60 m a. s.l. has poor storage abilities but good conductivity. Just above these elevations is an accumulation of a quantity of water that is interesting, with regard to hydropower utilization. At maximum groundwater levels, one part overflows into the neighboring aquifer (Fig. 4.108). Work on the design was completed in 2011 (Elektroprojekt, Zagreb). According to the design, it is foreseen to build an underground dam (grout curtain) from three galleries, of which the highest is at an altitude of 139 m (Paviša, 1998). The curtain is vertical with mutually folded (6 m) panels and a total area of about 300,000 m2. There is a hanging curtain in the central part, with the bottom contour at a depth of about 200 m; the sides are 130 m deep and enter into flysch at 5 m. The length of the dam’s crest is about 1500 m. For deep sealing of karst channels, large-diameter boreholes are planned, through which it is possible to insert large fractions and pieces of rock of different size. The installed capacity of the underground power plants is 68 MW. Specific problems are expected when performing sealing works deep below water level in channels with large flows and pressure variations, especially in the case of large and sudden precipitation. Particular technical problems are expected at zones of extreme tectonic destruction. These zones are discovered at the last stage of excavation of the access adit. Some of these zones are discovered behind a foreseen grout curtain route, at the area of ground water level in a dry period. Some of large carbonate blocks float in clay (Fig. 4.109a). In other cases, the clay is mostly washed out (Fig. 4.109b). If similar zones, with huge carbonate blocks, exist at the grout curtain routeit can be of great concern from underground dam construction point of view. This can be solved by construction of a massive cut-off wall, only. In the case of a submerged environment, including flowing water, it is a complex geotechnical task.

4.9 Underground Dam and Ombla Reservoir

273

350

350

300

300

250 82°

200

40°

B

B-5

C

107°

D

123°

E

F

137°

B-15 B-6

150 100

250 190°

A

B-12

1

100 3

50 0

T3

-150 -200

P-5

P-130

150

50

4

0 15.4°

14.6° 14.4° 14.2°

13.0°

E3

200

100

0° 15.

-50 -100

2

J,K

B-9

G

14.0°

6

-50 -100

5 -150 -200

-250

-250

-300

-300

Fig. 4.103 Profile along the Ombla underground dam axis 1. Boreholes drilled from surface 2. Karst channels and caverns 3. Level of underground storage 4. Exploratory gallery 5. Isotherm (To C) 6. Boreholes

Fig. 4.104 Horizontal (a) and vertical (b) contour of the cavern (karst channel) detected by application of SOCON instrumentation

drilled from gallery, T3—Triassic dolomites, J,K-Karstified limestone, E 3—Eocene flysch (Ravnik & Rajver, 1998, modified)

274

4 Water Resources Projects

Fig. 4.105 General concept of underground PP Ombla—layout 1. Axis of proposed underground dam 2. Overthrust fault 3. Faults 4. Ombla Spring 5. Dubrovnik River, K-Cretaceous limestone, J-Jurassic limestone, T 3 -Triassic dolomites, E 3—Eocene flysch (Milanović, 1989)

Fig. 4.106 Schematic outline of underground storage, cross-section

4.10

Tapped Springs, Local Water Supply Systems and Irrigation

Despite the exceptional wealth of water potential, the problem of water supply and irrigation was the historical threshold limiting development of this region. This is before everything related to the rural areas. Prevailing underground flows and the periodic activity of the springs resulted in a lack of water in the dry season. At that time, the only natural places with underground water were siphonic lakes in karst caves and shafts, if it was possible to provide access to water. The other possibility were tanks, in which water was

collected during a rainy period. Water was often transported with horses from distant sources. One of the characteristics of karst is that the karst aquifers are emptied through large but rarepermanent springs. This is why, for more significant urban areas, water was delivered from distant springs. One of the springs in this area that was tapped more in the Roman era is Vodovađa in Konavosko Polje. From the spring to Epidaurus (Cavtata), water was transported by a system of aquaducts and canals. At the end of the fourteenth century, in the period of summer droughts, Dubrovnik rented ships to bring water from the spring in Mlini.

4.10

Tapped Springs, Local Water Supply Systems and Irrigation

275

Fig. 4.107 General concept of underground HPP Ombla—crosssection. 1. Ombla Spring 2. Overflow dike 3. Dubrovnik River 4. Entrance into the Vilina cave 5. Gallery along the dam route 6. Vertical axis of underground dam 7. Access gallery 8. Caves behind the spring 9. Upper level of Vilina cave 10. Lower level of Vilina cave 11. Partof karst channels below the groundwater level 12. Position of karst channel detected by thermal logging 13. Overthrust line 14. Investigation borehole 15. Zone with possibility of deeper karst channels (Milanović, 1989)

Fig. 4.108 Schematic outline of underground reservoir 1. Aquifer discharge point 2. Lover part of storage volume 3. Upper part of storage volume 4. Low karstified or impervious rock mass 5. Section with pervious rock mass (overflow towards the adjacent aquifers) 6. Maximum groundwater storage level 7. Q/H graph (Milanović, 1989)

The first tapping structure for the city of Dubrovnik was made in 1436. Then, the craftsmen from Naples—Andriuzzi de Bulbito and Onofrio della Cava—captured the spring of Šumet between Komolac and Brgat. The length of the canal from the spring to the Mlini tank above Dubrovnik is 11,700 m (Fig. 4.110). The profile of the canal allowed a flow of 70 l/ s. From the water intake, at an altitude of 109 m, to the

reservoir above Dubrovnik (89 m a.s.l.), there was only a 20 m difference. From the reservoir to the well known Onofrio fountains in Dubrovnik, 14 mills were built (Beretić, 1963). In 1520, part of the tapping structure was expanded by tapping more springslocated along the contact of flysch/dolomite: Bota (earlier Knežica), Bračevica, Vrelo, Podvrelo,

276

4 Water Resources Projects

Fig. 4.109 Ombla Spring. Huge carbonate blocks in the background of the spring outlet (Photo Milanović, 2013)

Fig. 4.110 Tapped springs and traces of pipeline for Dubrovnik water supply constructed in 1436, Beretić, 1963 (Photo Onofrio’s fountain in Dubrovnik)

4.10

Tapped Springs, Local Water Supply Systems and Irrigation

277

Fig. 4.111 Old bucket elevators for irrigation from the Trebišnjica River

Vrijesna Glavica and Mračevo. The total length of the water supply canals after these works was 13,000 m. In the earthquake of 1667, the tapping structures were significantly damaged, and the mills were devastated. The first pumping from Ombla Spring started in 1897. Irrigation buckets were used for irrigation in the area of Trebinje (Fig. 4.111). They are mentioned in documents from the middle of the nineteenth century. Irrigation buckets were built on the part of the Trebišnjica River that did not dry out. Along Trebišnjica, from Kosjerevo to Mostaći, including the Pridvorci branch, 57 irrigation buckets were used for irrigation purposes; in Ljubomir, there were two and there was one on Trebišnjica spring for the needs of a fish farm. (Pujić, 2014). The hydrogeological characteristics of a number of tapped springs are described in Chap. 2 and here, only a short description is listed.

– Trebišnjica Springs is tapped for water supply of Bileća. Before the Bileća Reservoir, the tapping shaft was excavated behind the spring zone (Nikšićko Vrelo).

– Oko Spring, on the bank of Trebišnjica (now submerged by the Gorica regulatory pool), is tapped for water supply of Trebinje. – The tapping structure in Ljubomir, for water supply for the surrounding villages, consists of two wells with a capacity of about 25 l/s. – Bregava springs are tapped for water supply for Stolac and Ljubinje—directly from the spring. – The spring of the Gračanica River (Vratlo) is tapped for water supply for Gacko. – Jezdoš and Jedreš springs were tapped for water supply for Nevesinje (presently abandoned). – The siphonic channel of the Zovidolka River spring (Jama, near the village of Udbina) is tapped by a pumping well for Nevesinje water supply. – A well in the area of Vrijeka Spring in Dabarsko Polje is intended for water supply for construction sites of PP Dabar and also for Berkovići water supply. – A water tapping structure on the Srnj Spring, east of Gacko, is presently abandoned.

278

– South of Srnj, under the Avtovac—Gacko road, a well was drilled (through coal to limestone, 1973). Water was pumped into the Srnj tapping structure. It was abandoned because of H2 S content. – Ombla Spring is tapped for water supply for Dubrovnik (Croatia). Water is tapped directly from the spring. – The Duboka Ljuta (Robinson) Spring is tapped for water supply for Dubrovačka Župa, from Kupari to Cavtata and Ćilipi (Croatia), directly from the spring. – The Zavrelje pring in Mlini is used for water supply for Mlini (Croatia) and was used for a small hydroelectric power plant. – The Palata Spring was tapped for the water supply for Zaton (Croatia) and the hotels in Orašac. Productive wells are located in the immediate spring area. – A new catchment in Slano (Croatia) consists of two wells (B-3 with a depth of 85.5 m and B-4a with a depth 178 m). In the dry period, they are influenced by the sea (500 mg/l Cl). – Wells in the Doljani spring area serve for water supply for Metković (Croatia). The original capacity of the source of 18 l/s was significantly increased to more than 60 l/s after construction of the upper regulatory pool for RPP Čapljina in Hutovo. – Water from the connection valve on the head race tunnel close to the surge tank of HPP Dubrovnik in Plat is used for communal and agricultural needs of Konavosko Polje (Croatia) and water supply for Herceg Novi (Montenegro). In addition to those listed, a number of small permanent springs are simply tapped for local needs.

4 Water Resources Projects

25–30 m below the level of the riverbed. It has a width of 9 m, and a height of 2.5 m. In the karst channel, wells with installed pumps are drilled. The channel was investigated by divers, and it was determined that it continues in depth. The bottom of the siphon is at a much greater depth than the point where the wells penetrate the channel. The channel has not been explored to the deepest point of the siphon.

4.10.2 Vratlo Spring (Gračanica River): Gacko Water Supply Vratlo Spring of the Gračanica River was tapped in 1984 for water supply for Gacko and some villages (Fig. 4.114). The spring zone is located in the foothills of the Živanj mountain massif (elevation 1696 m), and the water discharges between the elevation of 1219.5 and 1231.0 m. The minimum measured flow is Qmin = 45 l/s. The maximum measured flow of the Gračanica River at the water gauging station before the entrance to Gatačko Polje is 145 m3/s. The length of the pipeline (Ø 300 mm) is 11,532 m. The key facilities of this system are Gacko 2 reservoir, with an elevation of the bottom at 1069.00 m and a volume of V = 1000 m3 (for consumers in higher zones—villages in the southeast municipalities) and Gacko 1 reservoir, with an elevation of the bottom at 1.023 m and a volume of V = 500 m3 (for consumers in the lower zone, including Gacko urban area and Mulja and Avtovac settlements). The tanks are mutually connected by the midfielder pipeline Ø 200 mm and length 550 m.

4.10.3 Water Intake for Ljubinje 4.10.1 Oko Spring (Eye Spring): Water Supply for Trebinje For many years, Oko Spring has been the main source of drinking water for Trebinje. From 1899, when the spring was tapped for the first time, until now, a large number of reconstructions and annexes have been created (1916, 1923, 1955, 1963, in 1972 and 1978). By building the Gorica Dam, the Oko Spring was submerged by an approximately 17 m water column, so the water intake was shifted to the slope above the reservoir level (Figs. 4.112 and 4.113). To select a new location, the necessary geological and geophysical research was done (method “charged bodies”) and in 1963, a new water tapping building was made on the slope, approximately 4 m above the maximum elevation of the Gorica regulatory pool (295 m above sea level). Here, the karst channel is located at a depth of

The water intake is at an altitude of about 130 m, directly at Bregava spring. Two pumps raise water at an elevation of 590 m to a reservoir with a volume of V = 800 m3. To the tank above Ljubinje, of the same volume, about 25 l/s is transported by pipeline, a length of 14 km.

4.10.4 Tappng Structure Palata Mali Zaton The first investigative works in the Palata Spring area were done by Geozavod: hydrogeological mapping, three investigation boreholes, discharge measurements and bathymetric monitoring. Investigative works into water tapping area continue in 1984–1986 (Milanović & Jokanović, 1987). The following investigation works were done: seven investigations boreholes; geophysical investigations;

4.10

Tapped Springs, Local Water Supply Systems and Irrigation

279

Fig. 4.112 Tapping of submerged Oko Spring. 1. Trebišnjica riverbed 2. Gorica reservoir level 3. Spring outflow 4. Old intake structure 5. Boreholes 6. New intake building 7. Wells 8. Karst channel 9. Karstified limestone 10. Fault (Milanović, 2000)

measurement of GWL; monitoring of sea tide fluctuations, drilling two pumping wells; and pumping tests to determine minimal spring capacity (Fig. 4.115). A minimal capacity of 100 l/s was established. The water tapping wells were made using the Benotto method. The depth of well V 1 is 19.70 m, with a diameter of 1000 mm. The well structure is made of roast-free steel,

with a diameter of 500 mm. Well V 2 has a depth of 15.00 m and is protected with steel construction; it has a diameter of 600 mm. In order to prevent sea penetration and salinization of water in wells along and beneath the existing dike (overflow weir), a concrete diaphragm was built, with a depth of 2.5 m and a thickness of 80 cm.

280

4 Water Resources Projects

Fig. 4.113 Oko Spring. Old tapping structure at Trebišnjica riverbank and the new building above the reservoir level

4.11

Tapping Structures and Water Supply Structures as Part of HET Activity

Due to investigative works regarding the design and construction of the Trebišnjica Hydrosystem (HET), which has lasted for more than 50 years, many tapping structures and water supply systems were implemented. Some of the water water tapping structures, which are intended to serve construction sites and construction settlements, also serve as the water supply for many remote villages. These are areas where, in ancient times, only shafts with water and cisterns provided the possibility of water for elementary vital needs in the dry season.

The depth of the well is 34 m, with a diameter of 300 mm, and it receives water from 21 to 31 m. The measured capacity of the well is 60 l/s, but the actual possibilities are much higher. Today, this spring serves as water supply to the Berkovići setlement and all the inhabitants of villages from Predolje (440 m above sea level) in the west to the village of Golobrđa (973 m above sea level) on the border with Montenegro. This includes the villages around Dabarsko and Fatničko Polje and the villages of Bilećke Rudine (Plana, Đeče, Orahovice, Podgorje, Selišta, Bogdašiće, Trnovica and Preraca). It is planned for water from this source to be distributed in the area of Vranjska and Krstač (1000 m above sea level). A system that distributes 30 l/ s consists of 280 km of pipeline, 21 pump stations and 17 reservoirs. With this system secured, there is water supply for about 1050 households (Vujović, 2021).

4.11.1 Vrijeka Spring For water supply (drinking and technical water) for future construction sites for HPP Dabar, a tapping well was constructed (1985) in the near background of Vrijeka Spring. Since the well did not enter directly into the cavernous zone with satisfactory discharge and the required capacity, a so-called shooting operation (blasting) was done at the bottom of the well, which established a connection with the water-bearing channels and improved well capacity considerably.

4.11.2 Jama: Udbine Spring From the Jama Spring, near the village of Udbine, discharges the Zovidolka River. The spring is tapped for the needs of drinking and technical water for construction sites, i.e., for HPP Dabar regulatory pool in Nevesinjsko Polje. The tapping structure consists of one well. The karst channel contains the water intake part of the tapping facility. During the pumping test for well Qav—26.55 l/s, the groundwater

4.11

Tapping Structures and Water Supply Structures as Part of HET Activity

281

Fig. 4.114 Spring of Gračanica River (Vratlo). Tapping structure for Gacko water supply

Fig. 4.115 Tapping structure Palata in Mali Zaton (a) Pumping test that defines the capacity of the spring (b) Dike between spring zone and sea, including shallow cut-off wall, 2.5 m deep (Photos Milanović, 1986)

282

drawdown was 9.01 m. This pumping lasted 253 h and totally exhausted 24,212 m3 of water. From this tapping structure, water is brought to the center of Nevesinje, with a pipeline length of about 17 km, as well as to the entrance of the head race tunnel for HPP Dabar and the Pošćenje dam site. As well as water for Nevesinje, water is also supplied to 220 households in the villages of Zovi to, Biograd, Rasta, Ljeskovik, Drežanj, Lukavica and Bezđeđa, with the ability to bring water to more than 500 households (Vujović, 2021).

4.11.3 Irrigation of Trebinjsko and Mokro Polje and Zupci Plateau The system of irrigation by irrigation elevator buckets enabled irrigation of arable land along the flow of the Trebišnjica River in Trebinjsko Polje for centuries. More remote areas such as Mokro Polje and especially Zupci plateau depended exclusively on the nature. The remote area of Ubla represents a significant recreation and touristic area, so there have been several attempts with local interventions (deep well) to solve the problem of water supply, however without success. Because of this, design and construction of a complex system for irrigation of these poljes and the Zupci plateau began (Vujović, 2002). The already built HET facilities are a good base for the mentioned system for irigation. Management and operation of the hydropower system, of which HET is a part, is very complex and depends on many planned and unplanned situations, when some parts of the system are temporarily not in operation. To provide operability and safety of the system, three water intakes are foreseen. One is in the tunnel for HPP Dubrovnik, another is in the Trebišnjica riverbed below Mostaći (upstream from the treatment plant), and the third is foreseen to be near the Geljov bridge or in the Ćatovića river branch (Potočina). The primary water intake, in the tunnel under Crnač, should work as a pumping station that presses water in the direction of Zasad, Mostaći, Pridvorci and Aleksina Međa and, in the other direction, towards Zgonjevo, Mokro and Abatno Polje and Kremeni do. The water intake in the Trebišnjica riverbed should be used to replenish the system in a period of increased consumption. In periods of regular overhaul, when the tunnel remains empty of water, it completely replaces the pumping station in the tunnel. In all working conditions, the pumps from both water intakes press water to the Obodina reservoir, from which water is pressed

4 Water Resources Projects

further toward the Zupci plateau (Fig. 4.116). For the vegetation period, when more than 90% of arable land needs water, there is the possibility of inclusion in the water intake system at the Geljov bridge or the water intake in the Ćatovića river branch. The system conceived in this way enables the irrigation of 1100 hectares of Trebinjsko, Mokro and Abatno poljes. The system also enables water to be distributed around the perimeter of these poljes and switches about 30 l/s on the Zupci plateau, where 5 m3 per household per day is planned. The area of the Zupci plateau is about 5400 ha, of which about 1200 ha is potentially arable land. This part of the system covers the water needs of 380 households, about 120 summer houses and the needs of recreational and tourist offers. The key facilities of the irrigation system are eight pumping stations and seven reservoirs, which are mutually connected with 180 km of primary and secondary pipeline networks. High capacity pumps are embedded in pump stations of the entire system, for irrigation during agricultural production. When the demand for huge quantities of water decreases, pumps of a smaller capacity can be activated, for water in settlements and water for greenhouses in the Zupci plateau.

4.11.4 Irrigation of Ljubomirsko Polje The tapping structure in Ljubomirsko Polje consists of two wells, with a depth of 36 m, a diameter of 200 mm and a total capacity of Q = 25 l/s (Fig. 4.117). Wells are located in the area of reverse contact, along which are rocks of Jurassic age, with a predominantly dolomite component overthrusted over Cretaceous limestone. This is the continuation of the Zupci fault zone that played a decisive role in the formation of the Lastva anticline. The Triassic dolomites that form the core of this anticline extend below this part of Ljubomirsko Polje. This formation does not appear on the surface; wells enter into it at depths of more than 20 m. In an area of reverse contact, a rocky mass is intensely tectonized, together with grusified Triassic dolomites, which have characteristics of almost intergranular porosity that enables storage of a significant quantity of water. Water from these wells enabled construction of a system for irrigation in the Ljubomirsko Polje and Mosko. The system consists of three reservoirs, several pumped stations and primary and secondary networks, which cover practically the whole area of interest for irrigation.

4.11

Tapping Structures and Water Supply Structures as Part of HET Activity

283

Fig. 4.116 Irrigation system for Trebinjsko and Mokro Polje, including Zupci and Ubla area

4.11.5 Water Intakes along the Trebišnjica Canal Apart from common tapping structures at springs or wells in the hinterland, larger springs and transformation of temporary flows into permanent flows for needs of the HET system sometimes make it possible for numerous consumers to have easy access to water. First, this refers to the formation of a permanent flow along the Trebišnjica riverbed (presently canal) through Popovo Polje that is about 60 km long. The

possibility of using this water for irrigation purposes is one of the significant socioeconomic benefits of this project. Intake structures along the paved (concreted) Trebišnjica riverbed are constructed at 17 locations. In some cases, these are serious tapping structures, with the purpose of taking the necessary amounts of water from the Trebišnjica that are, in natural conditions, unavailable in the vegetation period (Fig. 4.118).

284

Fig. 4.117 Ljubomirsko Polje, irrigation system 1. Production well 2. Spring 3. Group of ponors 4. Pumping station 5. Reservoir 6. Temporay flow of Brova River 7. Pipelines 8. Cretaceous limestone

4 Water Resources Projects

with interlayers of dolomites 9. Jurassic dolomites with interlayers of limestone 10. Reverse fault (according to D. Vujović)

References

285

Fig. 4.118 Tapping structures at the Trebišnjica riverbed in Popovo Polje, close to Ravno

References Aranđelović, D. (1966). Geophysical methods in solving some geological problems encountered in the construction of the Trebišnjica Water Power Plant. “Geophysical Prospecting” Vol. XIV. No 1. Aranđelović, D. (1970). Geophysics in civil engineering. (Geozavod). Vol. X/XI, Ser. C, Beograd.

Aranđelović, D. (1981). Identification of underground flow by application of method “Mise a la masse”. Second measurements. Report, not published, Geozavod, Belgrade. Aranđelović, D. (1984). Geoelectrical investigations at hinterland of Ombla Spring. Report. Not published. Bagarić, I., Kovačina, N., & Milanović, P. (1980). Application of gasious tracers for detection of karst conduite space position. Publication: Naš krš. Bulletin of Speleological Society of Bosnia and Herzegovina karst, 8.

286 Ballif P. (1896). Wasserbauten in Bosnien und der Hercegowina—I Teil, Meliorationsarbeiten und Cisternen im Karstgebilte. Printed in Vien. Bašagić, M, Šićarov, S, & Kalajdžić, Č. (1987). Fracturing of rock masses along tunnel Dabar-Fatnica. Proccedings, symposium: “Water and karst 86”. Beretić, L. (1963). Dubrovnik water supply system. Dubrovnik. In Croatian. Božičević, S., & Milanović, P. (1982). The large cavernes on the trace of hydro power tunnel route. In Proceedings. VII Yugoslav symposium on hydrogeology and engineering geology. Cvijić, J. (1926). Geomorfology II. Dašić, T., & Vasić, L. J. (2020). Flood protection and water utilization of karst poljes: example of Gatačko Polje, Eastern Herzegovina. Environmental Earth Science, 79(233), 1623–1633. Đerković, B. (1966). Hydrogeological properties of Nevesinje closer vicinity. Herald Geological No 11. Gašparović, R. (1979). The contribute of speleologists of Bosnia and Herzegovina at construction of some hydro power structures and scientific investigations in karst. Naš krš, Bulletin of Speleological Society Bosnia and Herzegovina karst, No. 7. Kovačina, S., & Miljković, E. (2004). Development of Hydropower System in Trebišnjica river basin. Presentation: Round table, HET. Lazić, A. (1927). Ponors and estavelles in Popovo Polje. Herald of Serbian Geographic Society. 13. Mikulec, S., & Praštalo, B. (1965). Gorica Dam. Symposium: Construction of Power System “Trebišnjica”. Milanović, P. (1971). Upgrade of Klinje Dam structure. Geology, Investigation works. Documentation of HET. Milanović, P. (1975). Hydrogeology of Ombla Karst aquifer. Master theses. Mining–Geology Faculty, University of Belgrade. Milanović, P. (1976). Application of radioactive tracers for determination of zones with undeground flows in Eastern Herzegovina karst area. PAPERS 3rd International Symposium of Underground Water Tracing (3. SUWT). Milanović, P. (1977). Hydrogeology of the Ombla spring drainage area. Herald Geological, 22. Milanović, P. (1980). Possibility of application remote sensing in karst hydrogeology. Doctor theses, Mining - Geology Faculty, University in Belgrade. In Serbian. Milanović, P. (1981). Karst Hydrogeology. Water Resources Publication. 434 pages. Milanović, P. (1986). Hydrogeological and engineering geological problems of hydrotechnical construction in karst. In G. Gunay & A. I. Johnson (Eds.), Karst Water Resources (Vol. 161). Milanović, P. (1987). Hydrogeologic and engineering geologic problems of hydrotechnical constructions in karstified rock masses. Vodorivreda 19. pp. 271–285. Milanović, P. (2000). Geological engineering in karst (p. 347). Zebra Publishing Ltd. Milanović, P. (2003). Prevention and remediation in karst engineering. In B. Back (Ed.), Sinkholes and the engineering and environmental impacts of karst. ASCE. Milanović, P. (2006). Karst of Eastern Herzegovina and Dubrovnik Littoral. ASOS. Milanović, P. (2009). Study on Hydrogeology of Nature Park Hutovo Blato. WWF European Policy Programme. Milanović, P. (2010). Transboundary aquifers in karst–source of water management and political problems. Case study, SE Dinarides. ISRAM.

4 Water Resources Projects Milanović, P., & Jokanović, V. (1987). Tapping the spring that is under influence of sea tide. Proccedings of articles: IX Yugoslav Symposium on hydrogeology and engineering geology. Milanović, P., Vučić, M., & Jokanović, V. (1987). A cavern around powerplant headrace tunnel tube. Groundwater effects in geotechnical engineering. A.A. Balkema, Rotterdam/Brookfield. Milanović, P. (1989). PP Ombla, Basic design, Geology, Book I i II. Energoprojekt. Milanović, P., Glišić, R., Đorđević, B., Dašić, T., & Sudar, N. (2012). Impacts of partial water re-routing from the Buna and Bregava catchments in the catchment of Trebišnjica River. In Summary in English, Vodoprivreda. 44, pp. 3–23. Mladenović, J. (1966). Influence of geolythological properties on water chemistry in Popovo Polje region (Trebišnjica). Herald Geological No. 11, Sarajevo. Niva, B. (1990). Results from borehole radar tests in Ombla tunnel. Unpublished Report. Paviša, T., & Mucović, R. (1979). Application of shotcrete for remediation of Trebišnjic riverbed. XI Congress for large dams (JKVB). Paviša, T. (1998). Underground reservoir in karst terrine. In Hrvatske vode, 14-25. Petrović, B. (1965). Experimental plugging the estavelle Obod in Fatničko Polje. Fund of documentation HET. Pujić, S. (2014). Irrigation water buckets at Trebišnjica. Center for informations. Ravnik, D., & Rajver, D. (1998). The use of inverse geotherms for determining underground water flow at the Ombla karst spring near Dubrovnik, Croatia. Journal of Applied Geophysics, 39(3). Roglić, J., & Baučić, I. (1958). Karst of dolomites between Konavosko Polje and sea coast. Geography Herald, No. 20. Sikošek, B. (1954). Tectonic of the area Bileća–Trebinje. Publication of Geological Institute “Jovan Žujović”, Book, 7. Belgrade. Skopljak, E., & Kovačina, N. (1978a). Micropulzation of pressure in monitoring piezometers and possibility to foressen change of groundwater level. (Stage I). Institute for hydrotechnic of Civil Engineering Faculty in Sarajevo. Skopljak, E., & Kovačina, N. (1978b). Diagram of cyclic changing of air current direction from piezometric borehole A-5 during rapid water table increasing. Stojić, P. (1966). Bearing capacity and stability improvement of the left bank of the Grančarevo Dam. Proceedings: VII JKVB. Stojić, P., & Karamehmedović, E. (1970). Grout curtain Grančarevo. Proceedings: VIII Congress JKVB. Stojić, P., Fingerhut, L., & Šimić, T. (1976). Tail race tunnel of RPP Čapljina, remediation of underground water burst. Working Papers of the First Yugoslav Sympsium for the Soil Consolidation (JUSIK ‘76). Šarin, A., Radić, J., & Škaberna, I. (1965). Hydrogeology of Hutovo blato area. Report. Geoistraživanja-Elektrosond, Zagreb. Uljarević, M., Jokanović, V., & Traparić, R. (2003). Report on finalisation the investigation works including suggestions for remediation of seepage waters at the dam site Gorica. HE Trebišnjica. Vujović, D. (2002). Irrigation system for Trebinjsko,and Mokro Polje including Zubci and Ubla area. Executive Design, not published. Trebinje. Weiler, T., & Rick, W. (2005). Ombla Spring. Results of the Cavity Survey by means of Echo-Sounding in the cavity. SOCON Sonar Control Kavernenvermessung GmbH. Giesen. Zubac, Ž., & Bošković, Ž. (2012). Problems of watertightness of Gorica Reservoir–Trebinje. Vodoprivreda, 44, pp. 273–276.

5

Influence and Consequences of Water Resources Projects

Dabarsko polje, Vrijeka Spring

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. Milanović, Karst of East Herzegovina and Dubrovnik Littoral, Cave and Karst Systems of the World, https://doi.org/10.1007/978-3-031-28120-4_5

287

288

5.1

5 Influence and Consequences of Water Resources Projects

Introduction

Centuries of life experience unequivocally points to the conclusion that, due to the nature of karst and uneven distribution of extreme precipitation, socio-economic development of East Herzegovina is not possible without regulating the unfavorable natural water regime. This can only be accomplished with construction of a complex multipurpose water management system that favors the cascading position of karst poljes. Previous experience with such interventions in similar hydrogeological/hydrological conditions did not have a stimulating effect. Withthe impression of numerous failures in karst terrain but also big problems when a project became operational, even the professional public was skeptical. In spite of so skeptical opinion the creators of the Hydrosystem concept, and those who accepted it, were aware of this idea and strongly believed in it. It was clear from the very beginning of the design and realization of the Trebišnjica Hydrosystem that, along with huge positive effects, there would also be some unintended negative consequences. It was also clear that some of these consequences could be predicted in advance, but that unforeseen and unwanted consequences would also occur. It should also be mentioned that the nature of the karst of Eastern Herzegovina is one in which the reactions of nature to changes in the natural water regime can be unpredictable and often drastic. This is best illustrated by the short phrase ‘expect the unexpected’ during each intervention in karst, especially if there are regional interventions. The positive effects of a regulated water regime are immeasurable: the possibility of optimal management, improved water supply, improvement in agriculture, energy utilization, preservation of ecosystem, improvement in the existing demographic trend, formation of permanent water surfaces, tourism and improvement in standards of living. Realization of a complex project in karst, which by regional scales and technological complexity is among the most challenging types of projects in the world, requires a long period of time. This is why, even when most of it is in operation, all of its advantages are not realized, even in the already-built part. This is the case with a key problem— floods. Undoubtedly, the already-built part of the infrastructure significantly contributes to a reduction of floods, but that still is not in that one level to whom tends project. With construction of the Grančarevo and Gorica dams and the Bileća and Gorica reservoirs, with a tunnel towards HPP Dubrovnik, the water regime is changed to some extent, both upstream (Fatničko and Bilećko polje) and downstream (Trebinjsko, Mokro and Popovo Polje). With the construction of RPP Čapljina, a permanent Trebišnjica flow was formed and the floods in Popovo Polje are significantly reduced, both in terms of the number of occurrences and

the submerged area area. Permanent river flow enabled irrigation of agricultural areas in the growing season. Instead of an agricultural season which, in natural conditions, is “100 days maze” (vegetation period of 90 days), with the possibility of an early flood destroying it, now it enables production of wide spectrum of agricultural products (Fig. 5.1). The most common potential negative consequences of this complex intervention include the following: submergence of arable land and infrastructural facilities, immersion of culturally important historical monuments, impoverishment of karst aquifers, changes in natural discharge of karst springs, deterioration of the quality of underground and surface waters, vulnerability of endemicand other fauna, provoking induced seismicity, formation collapses on the terrain surface and more secondary questionable consequences. There are numerous positive effects of the construction of the multipurpose Hydrosystem in Trebišnjica that are given through the previous chapters. Some of the mentioned consequences, both positive and negative, are described in the text that follows. Electric power is not a subject of consideration in this text, but it should be emphasized that its role in the development of East Herzegovina is indisputable, especially now, when part of the system is already in operation.

5.2

Submerging of Living Space, Agricultural Land, Archaeological Sites and Infrastructure

A basic condition for even development of East Herzegovina is regulation of the natural environment water regime, i.e., eliminating dependence on floods and droughts. This is possible only with construction of a unique water management multipurpose system, with positive effects in all parts of the region. It is clear that this kind of complex system, by which natural characteristics are significantly changed at a regional scale, is not possible without certain consequences, both natural and man-made. Conception of the system, with waterproof reservoirs for multi-annual periods of flow regulation, was also dictated by the nature of karst. By the realization of key structures of the HET system, the Grančarevo Dam and Bileća Reservoir, the biggest sacrifice was made but, at the same time, the largest contribution for regional development was given. By construction of the Grančarevo and Gorica dams, that is, the Bileća and Gorica reservoirs, the largest part of the permanent flow of the Trebišnjica River and Miruša valley is submerged. Along with immersion of agricultural land and emigration of the population, one of the most significant ethnological spaces with numerous archaeological localities and cultural monuments disappeared (Fig. 5.2).

5.2 Submerging of Living Space, Agricultural Land, Archaeological Sites and Infrastructure

289

Fig. 5.1 Popovo Polje. View from Ravno towards upstream. (Photo Milanović)

Fig. 5.2 Trebišnjica valley downstream of spring zones (a) in natural conditions, 1970 and (b) during reservoir empting in 1983 (Photo Milanović)

From the reservoir space, 398 households with 1625 inhabitants were removed, and 3658 ha of land was submerged, from which 420 ha of arable land and 12 ha of arable land had vineyards. Thirty-seven km of narrow track railway lines were displaced. In this space, more than 200 prehistoric tumuli were recorded, a dozen ancient settlements, a large number of

medieval stećaks (Middle Age monumental tombstones) and the remains of Roman communications (roads and bridges). Between ancient settlements, there was a Roman settlement in the area of Panik, with a Roman temple and a rustic villa, with rooms decorated with mosaics and equipped with hypocaustic heating (Sivrić, 1972). About 100 selected stećaks were transferred to Bileća.

290

5 Influence and Consequences of Water Resources Projects

Fig. 5.3 Ruins of Kosijerevo monastery inside the Bileća reservoir, and after displacement at the new location on the left reservoir bank, 1983. (Photo Milanović)

From the reservoir space, the Dobićevo monastery, built in 1232, was displaced. It was a complex undertaking, with removal of frescoes and dismantling of the building stone by stone. The monastery was reconstructed near the village of Orah, which was also partially submerged. Installation was a particularly complex conservation work, placing the original frescoes on new monastery walls. The Kosijerevo monastery, built in the first half of the fourteenth century in Montenegrin Miruše, was moved to the left bank of the Trebišnjica, in the area of Petrovići (Fig. 5.3). The impressive structure of the Arslanagića bridge, which was built in the second half of the sixteenth century (completed 1573/74) as an endowment of Mehmed Pasha Sokolović, was also dismantled stone by stone and moved from the Gorica reservoir space to a new location, downstream from the Gorica Dam (Fig. 5.4). With the Gorica Reservoir, Oko Spring and the water tapping structure for water supply of Trebinje were submerged. The water tapping and water supply facilities for the Kosijerevo railway station, at the Trebinje—Bileća line, and the water tapping structure at Trebišnjica spring for water supply for Bileća were also submerged.

Oko spring was displaced above the level of Gorica lake (Sect. 4.10, Figs. 4.111 and 4.112). A water intake well was dug in the background of Trebišnjica springfor the water supply of Bileća. Some structures, such as the stone railway bridge near the Arslanagića bridge railway station, remain under water (Fig. 5.5).

5.3

Reservoirs and Permanent Surface Flows

In the dry period in East Herzegovina, significantly reduced river networks existed, related to the humid period of year. – Trebišnjica River then flows from the spring (Dejan’s cave) to Dražin do. In the dry period, downstream from Dražin do, the flow dries up for a length of 65 km. – When the rain stops, the Zalomka River decreases to an insignificant flow from Fojnica to Crni Kuk, and it dries up over 45 km, from Crni Kuk to the Biograd Ponor and more than 5 km upstream from Fojnica.

5.4 Increasing the Minimum Flow through the Town of Stolac

291

Fig. 5.4 Arslanagić Bridge, displaced from the original location to the presentlocation

– More than 20 km of the 33 km of the Bregava River dries up in summer. – The flow of the Mušnica River (with Gračanica) dries up in the summer through Malo Gatačko Polje and, through the large Gatačko Polje, flow is considerably reduced. With the construction of the Grančarevo Dam, the Bileća Reservoir (Bileća Lake) was formed, with a surface of 27.6 km2. With three more reservoirs (Gorica, Hutovo and Svitava), East Herzegovina had a total of about 40 km2 of water surface. With construction of the RPP Čapljina, the temporary flow of the Trebišnjica River through Popovo Polje was transformed into permanent flow, with a surface of 12–19 million m2, depending on flow discharge. In the first years after completion of the first phase of HET, there were already indications that these water surfaces have an impact on microclimate and vegetation renewal. Daily evaporation up to 10 mm was measured from these water surfaces during summer. Mean monthly increase of relative air humidity for the period of time after the reservoirs were created was also measured: Bileća 12%, Lastva 5% and Berkovići 7%

(Milićević & Krga, 1978). A larger number of days with the occurrence of fog were also noted. In order to confirm and quantify the influence of the newly formed water surfaces on the microclimate, a longer period of observation and a measurement series of meteorological and hydrological parameters is necessary.

5.4

Increasing the Minimum Flow through the Town of Stolac

The key characteristics of the spring zone and Bregava discharge is shown in the chapter about the Bregava River (Sect. 2.1.20). The Upper Horizons project envisages the transfer of part of the water from the Bregava catchment in the Trebišnjica catchment. Numerous ponors in Dabarsko Polje will be rehabilitated, and the most important ponor zone of Ponikva will be isolated and arranged for controlled enagaged water in the ponor. This will cause a change in the natural regime of the permanent spring and flow of the Bregava. As in most similar cases, these change refer to the

292

5 Influence and Consequences of Water Resources Projects

Fig. 5.5 Railway bridge submerged by Gorica Reservoir. (Photo R. Putica)

Fig. 5.6 The leakage diagram from gauge station Do that the 8 km downstream

maximum and average discharge of the spring, while the minimum will remain approximate at natural values. A specific problem is found in the flow of the Bregava through the Stolac area. Because there is distinctly uneven flow, especially through the urban part of Stolac, problems of an ambient and ecological nature arise. In the dry period, discharge of Bregava Spring can drop to 400–500 l/s, which was proven by measurements in 1986. This takes place at the end of a long dry period, when the Ponikva Ponor in Dabarsko Polje sinks 100–150 l/s and, at an extreme minimum, 50 l/s. Then, the discharge of the source depends

primarily on retardation of the immediate catchment area and less comes from the catchment north of Dabarsko Polje. Under these conditions, because of seepage through the river deposits and karstified rocky mass under the river sediments, more than half the water flow is lost before Stolac. Seepage is between 0.5 m3/s and 0.8 m3/s only in part of the flow, 4 km downstream from the water measuring station Do. This is confirmed with more simultaneous hydrological measurements along the flow, at different discharges (Fig. 5.6). At larger flows, discharge through the riverbed in that section loses up to 0.8 m3/s. This is a section that needs

5.5 Natural and Induced Collapses

rehabilitation works to prevent water losses. Along the next 4 kilometers (from the fourth to eighth kilometer) losses are smaller but minimal flow leakage is almost negligible. In order to eliminate the losses along the riverbed and to enable flow of at least those quantities of water that naturally discharge at the spring through the urban part of Stolac during the driest period, it was necessary to carry out certain geotechnical works along the riverbed. Investigations were carried out from 1972–1975, in order to select the optimal solution. The key works were the following: geological reconnaissance of terrain, geophysical investigations (geoelectric sounding), exploratory drilling and tracer tests of one borehole. Five exploratory boreholes were drilled along the riverbed, with a depth from 18 to 42 m. Piezometer tubes were installed in all of them. In order to determine the general direction of water flow that sinks in part of the bed downstream from the water gauging station, 40 kg of Na-fluorescein was injected into borehole BR-1 (11.8.1975). The level of water in the piezometer was at a depth of 34 m, compared to the flow level. The presence of dye was registered in the Drijen Spring, on the northeast rim of Deransko blato. The position of the investigative boreholes is given in Fig. 2.37, and a geological cross-section downstream from WGS Do in Fig. 2.39. These works were part of the activities in the Upper Horizons project. This project should enable an increase of approximately 1 m3/s, in relation to natural minimum discharges, through Stolac, by introducing part of the transferred water from the level of Nevesinjsko Polje. In this way, the current minimum flow would significantly increase, whichwould significantly improve the ambient and ecological characteristics of that part of the Bregava River. This is why geotechnical solutions should be chosen that will meet the requirement of waterproofing and, as much as possible, keep the natural characteristics of the riverbed. At the same time, the realization of the Upper Horizons project would reduce the natural extreme flows that threaten the banks and bridges in the urban part of Stolac. The project foresees that, in the vegetation period, which most often coincides with drought, priority will be production of food and environmental requirements over energy, i.e., irrigation of Dabarsko Polje and regulated increase of flow through Stolac has an advantage over power production.

5.5

Natural and Induced Collapses

In the karst poljes of East Herzegovina, collapses often occur in natural conditions and as a consequence of technical structures in reservoirs, in the tunnel routes and along the

293

canals. They are a dangerous occurrence because they are practically unpredictable, and the majority happen abruptly. The genesis of the majority of natural collapses is described in Chap. 1. Natural collapses are, above all, a consequence of flooding of karst poljes (Popovo, Fatničko and Cerničko), by forming artificial reservoirs that are characterized by frequent and fast fluctuations that accelerate the process of formation and increases their number. They are a consequence of the process of suffusion and erosion in the alluvial sediments above the ponors and ponor zones in the paleo-relief. After the collapse occurs, the old ponor is reactivated and, through it, water is lost from the reservoir. The most famous world example is the collapse in the Keban Reservoir in Turkey where, after the collapse, eakage of 26 m3/s began, through the reactivated karst channel (cave). During the first experimental filling of the Hutovo regulatory pool for RPP Čapljina, there were a large number of collapses, i.e., the formation of new sinkholes with ponors at bottom. There were newly registered sinkholes in 1975 (38), in 1977 (44), and in 1980 (36). Figure 5.7 displays two collapses that occurred after the first filling of Hutovo regulatory pool. These collapses were remediated by clay-cement mass. After 1980, the reservoir has not been emptied for many years, so new sinkholes have not been registered, meaning the process of their formation definitely stopped. In October 1986, on the right bank of the Bileća Reservoir at the Panik location, below the village of Orah, several collapses were registered, at about an elevation of 387 m (Fig. 5.8). The largest collapse with the largest opening at the bottom was equipped with a vertical pipe laid ten meters above the ground. A tracer test was carried out when the reservoir level was 5–6 m above the collapse zone, but it did not establish a connection with Stara Mlinica or other downstream springs. Labeled water appears in the reservoir area only. This was furtherconfirmation that the Bileća Reservoir was formed in a closed hydrogeological structure, from which there is no possibility of water losses. Thirty years later, an increase in some of the existing collapses and origination of new collapses occurred, and the research was repeated in 2016/17. (Milanović & Vasić, 2018). Dye tracer was injected into eight collapses/ponors and a connection was established only with the reservoir. These works included speleological prospection of the Stara Mlinica temporary spring. About 90 m of the karst channel was explored speleologically. These works confirmed that the sub-catchments of Orah and Mosko are isolated hydrogeological entities, in which the karstification process is directed exclusively towards the riverbed of Trebišnjica. These sub-catchments are separated from sub-catchment Stara Mlinica (Jasen and Budoši area) by a structure with a core that makes the dolomites of the Lastva anticline

294

5 Influence and Consequences of Water Resources Projects

Fig. 5.7 Collapses at the bottom of Hutovo Reservoir (regulation pool) that occurred during the first reservoir filling, 1975 (Photo Milanović)

watertight. They completely prevent the hydrogeological connection between the right bank of the Bileća Reservoir and the Stara Mlinica spring. Present collapses in Panik, which arose after formation of the reservoir; in neither case does it threaten watertightness (Fig. 5.9). When it comes to the new collapses in the area of Panik, it should be noted that in the Roman era there existed significant settlements with arranged infrastructure. Over time, part of this area was turned into agricultural land. There is now the question of possible impact of certain structures (sewage system) from the Roman period on the formation of these collapses. Immediately after started operation of RPP Čapljina and head race tunnel become under pressure (1979), turbid water appeared at several sources along the edge of Sitava. Muddy water contain 20% of suspended clay particles. On the surface, about 50 m above the tunnel, a collapse occurred, with a diameter of about 10 m. Investigations showed that stability of the tunnel tube was seriously threatened because it was left without support for a length of approximately 17 m. Investigative and remedial works to ensure the stability of the tunnel are shown in Chap. 4, Figs. 4.78 and 4.79). The formation collapse on the surface occurred during excavation of the Fatnica—Bileća tunnel, downstream from the intake structure in Fatničko Polje.

5.6

Consequences of Water Regime Change

5.6.1

Impoverishment of Karst Aquifers

One of the goals of the Trebišnjica Hydrosystem is to reduce underground water flows and to keep the water on the surface as long as possible. A large part of the water now flows towards the sea and to the Neretva valley through tunnels and watertight channels (structures of the first phase of the HET). Numerous ponors and ponor zones are sealed or are otherwise isolated and prevent direct infiltration and recharge of the karst aquifers. The most expressive examples are Doljašnica, Pasmica, Crnulja and Provalija. Activity of underground flows in the karst systems of these ponors now depends only on the rainfall in their immediate catchment area (between the ponors and discharge localities). It is obvious that the relationship of surface water and underground water after construction of the first phases of the HET system has been significantly changed. With construction of the first phase of this system, around 4 billion cubic meters of water per year flows to the sea, directly through the hydraulic tunnels. At that amount, there are depleted karst aquifers downstream from the structures of the first phase.

5.6 Consequences of Water Regime Change

295

Fig. 5.8 Sinkholes (ponors) in the right bank of Bileća Reservoir, in the area of Panik, 1986 (Photo by Milanović)

It is estimated that, after the system is fully completed, some karst aquifers of Eastern Herzegovina will be depleted by about 6 billion cubic meters of water per year. Based on current knowledge, it is very difficult to predict which long-term consequences will occur in the karst aquifers, thinking first of all about intensity of karstification process development and survival of endemic species. One of the frequent questions is related to the huge quantity of suspended particles and heavy sediments which flood the water brought into the underground through numerous ponors. This water discharge in the downstream springs, with relatively clear or completely clear water, rarely turbid. By construction of the HET system, floods will be reduced. Only in periods of rare extreme hydrological situations will transport of suspended material into the karst underground be significantly reduced. Compared to the natural state, this is a

significant change. Since this phenomenon has not been sufficiently analyzed in its natural state, it will be difficult to monitor the consequences of newly created conditions.

5.6.2

Influence on Downstream Springs and Submarine Springs

The question of the impact of construction of the HET on downstream springs was raised on the same day as the implementation of this project. In 1960, 5 years before the first structures were built, the spring cadastre was completed, and the monitoring system was established. This cadastre includes almost all major springs from Konavosko Polje to Deransko Blato, a total of 120 springs (Ramljak, 1978). It was scheduled to start in 1960, with permanent and

296

5 Influence and Consequences of Water Resources Projects

Fig. 5.9 Bileća Reservoir, right bank, Panik area (a) Area with collapses indicated by arrow (b) Collapse area—larger scale (Google Earth, 28/10/ 2019)

temporary monitoring of 46 springs. In the case of a reduction of minimum spring discharge, the HET’s obligation was to compensate for the damage caused by system operation. Because of that, special attention was paid to measurements of minimal discharge. Some significant springs are equipped with water gauging facilities. In 1961, for further observations, 16 springs were selected as the most important springs. That program was later expanded to other localities in the Neretva valley, and a total of 26 springs were monitored. Through long-term monitoring, including tracer tests and release of water from Gorica reservoir in the dry period, it was established that springs in Palata, in Mali Zaton, Orašcu, Trstenom, and Slanom i Oku in the delta of the Neretva River have their own catchments and they are not connected with the Trebišnjica catchment. This is in contrast to Konavoska Ljuta, Duboka Ljuta, Zavrelje, and Ombla, submarine springs between Banići and the Malostonski Bay, as well as springs around the edge of the Neretva valley and Hutovo Blato, where that connection has been proven. Through long-term observations, it was unequivocally established that the construction of HET did not endanger the natural minimum discharge of any spring, nor did it cause drying up of any spring. Regime changes generally have the effect of reduction of maximum flow and average annual discharge. The Ombla Spring—the source of the Dubrovnik River—is a good example. In natural conditions, the medium annual discharge of this spring was Qav = 33.8 m3/s. After the construction of the first phase of HET, including RPP Čapljina, with most facilities being located in the catchment area of Ombla, the average annual discharge is reduced to Qav = 24.7 m3/s (for a period of 40 years, since the filling of the Bileća Reservoir). However, no impact on minimal

discharge was found, but a multy annual period of flow regulation was observed, i.e., a reduction of differences between Qmin and Qmax. At the Doljani Spring near Metković, there were indications of reduction of minimal discharge. However, after construction of the Hutovo regulatory pool, the capacity of the Doljani spring zones increased, in direct connection with losses from Hutovo Reservoir (regulatory pool). Questions also appeared about the possibility of intensifying the intrusion of sea water deeper into the alluvium of part of the Neretva River delta, and part of the karst area being released. There was significantly reduced groundwater inflow as a consequence of civil works at very end of Popovo Polje, in the springs from Doljani to Kuti. There are also indications that, in some cases, the influence of the hydrosystem on minimum spring discharge is positive, due to losses from reservoirs and a hydropower tunnel under pressure. It is likely that the losses from the Gorica compensation pool and tunnels for HPP Dubrovnik have a positive effect on the low waters of Robinson and Zavrelje. Losses from the Hutovo regulatory pool affect the minimal discharge of spring zones in the Neretva valley and along the edge of the Svitava depression. An interesting example is the temporary spring Lušac in Trebinje. After construction of the Gorica regulatory pool, it became a permanent spring. Restoration of the natural regime of this spring now occurs only during periods of emptying of Gorica pool and tunnels; however, this happens rarely and is short lived. In addition to the springs, the impact of HET on the submarine springs in Maloston Bay was also analyzed (Ramljak, 1978). In the case of Provalija ponor zone, the

5.6 Consequences of Water Regime Change

question was about the influence of elimination of activity on seawater salinity, transparency and temperature, and transport of nutrients from Popovo Polje into Malostonski Bay. There was doubt that these changes provoke negative influence on the cultivation of shellfish (oyster and mussel). Longterm and detailed investigations were carried out with the participation of experts from Split, Kotor and France. The collected results were often interpreted in opposite ways, but the prevailing opinion is that there is no negative influence.

5.6.3

Consequences of Trebišnjica Spring Submergence

One of the more significant questions that was considered during determination of maximum elevation of Bileća Reservoir and its water permeability was related to the Trebišnjica springs submergence. At full reservoir (elevation 400 m), the spring zone of Trebišnjica (elevation 325 m) was submerged with a water column of 75 m, so it was necessary to evaluate the consequences of this immersion. The most significant questions were: – Is it possible for high reservoir levels to occur in underground overflow towards the Bregava River catchment, whose springs are about 200 m lower than the springs of Trebišnjica? That is, is there a possible risk of water loss from the reservoir? – Which consequences provoke submergence of springs (floods) in Fatničko Polje? – How do high reservoir elevations affect the levels of underground water and floods in Bilećko Polje? In order to answer the question about possible losses from the Bileća Reservoir, the location of the watershed between the catchments of Trebišnjica and Bregava springs had to be determined. It was clear that the orographic watershed does not exist here. Extensive investigative works were carried out: geological mapping, tracer tests, geophysical investigation works in Fatnički Polje and south of it, and drilling of deep investigative boreholes in the zone of the assumed watershed. By dye tracing of water that sinks along the southwest rim of the polje, the bifurcation zone was established (Fig. 1.69). Geophysical research (geoelectric sounding) indicated a high base of karstification, that is, an underground watershed zone. The presence and position of this zone was confirmed by investigation drilling. Hypsometrically, the highest position of the underground watershed zone (above 400 m), which is made up of compact limestones and dolomites, is located between boreholes K-1 and F-3. These rock masses are not affected by the process of karstification and function well as a watershed zone. Existence of these watershed zones was confirmed during the

297

long operation of the Bileća Reservoir. Even at the highest elevations, there is no possible reservoir overflow water or losses towards the Bregava springs. Even before the first filling of the reservoir, it was clear that spring submergence and fluctuation of the reservoir level will have certain consequences on the water regime in the karst aquifer in the hinterland. The question was how far that influence would extend and whether it would reflect on the hydrological regime of Fatničko Polje. The height difference between the Fatničko Polje bottom and Trebišnjica springs is 137 m. Maximum reservoir level is 32 m higher than the minimum level of underground water in the area of Fatničko Polje. By monitoring of fluctuation for many years, the level of underground water in boreholes PB-1 (12 km upstream from the Trebišnjica springs, Figure 5.10a and c) and in piezometers of the broad area of Fatničko Polje, it was determined that a full reservoir affects the discharge dynamics of the karst aquifer. In periods when the elevation of the reservoir is between a 390 and 400 m decrease (recession curve) of underground water level in the area of PB-1, from an elevation of 500 m to 450 m, requires twice as long as under natural conditions (Figure 5.10b). Based on the analysis of a large number of decreasing cycles, it was determined that, under the same hydrological conditions and for the same amount of lowering of the aquifer level, before the reservoir was created required about 150 h but in cases of a full reservoir is about 300 h. By comparison diagrams of Fatničko Polje dewatering for periods before and after reservoir construction, Milićević (1976) established that elevations of the Bileća Reservoir, lower than 360 m above the sea, do not affect the water regime in the polje. According to the analyses of Paviša (1985), before the reservoir (1949 to 1967), floods in Fatničko Polje lasted 130.4 days and after construction of the Grančarevo Dam, 148.4 days (1968–1982). However, analysis done in1968–2004 shows that the average duration of floods for that period was 125.3 days. Based on these data, it is difficult to draw a definitive conclusion about the impact of the Bileća Reservoir on length of duration and height of floods in Fatničko Polje.

5.6.4

Characteristic Floods of Bilećko and Popov Poljes after 1968

The water regime between Fatničko and Bilećko polje is a direct consequence of submergence of the Trebišnjca springs, shown in the foreword subchapter (5.6.3). During the observation period so far, the enabling data collected make it possible to define the extent of the impact of the Bileća Reservoir on the immediate hinterland of the spring, that is, on Bilećko Polje. It is known that, under certain situations, a part of Bilećko Polje floods. For

298

5 Influence and Consequences of Water Resources Projects

Fig. 5.10 Piezometer PB-1 (a) Layout (b) Water table recession curve in borehole PB-1 under natural conditions (1) and after impounding of Bileća Reservoir (2). (c) Cross-section from PB-1 to Bileća Reservoir (Milanović, 1986)

Fig. 5.11 Cross-section, Bileća Reservoir (Ombla Spring)— perimeter of polje

monitoring of the impact of the reservoir on piezometric levels below the polje surface, several piezometric boreholes were drilled in the polje area (Figs. 5.10 and 5.11). One of them is PL-1, in the lowest part of the polje in Duboki do (deep sinkhole) with a bottom elevation of 408.52 m. From 1968–1982, there were 21 occurrences of water in the lowest part of Bilećko Polje (Duboki do), while actual

flooding of the polje was registered only three times, in 1970, 1979 and 2009/2010. There is no doubt that the coincidence of high elevation of the reservoir, high rainfall and high inflows into the reservoir cause the level of underground water to rise and floods to occur in the lowest part of the polje. Figure 5.11 presents a cross-section with piezometer lines at different levels of the reservoir with different inflows.

5.6 Consequences of Water Regime Change

299

Fig. 5.12 Bilećko Polje, inlet into the drainage tunnel

Analysis of the flood in 1970 confirmed that the springs along the northern rim of the polje, in the area of Podosoje, appear when the reservoir is full and inflow into the reservoir is greater than 250 m3/s. The estimated amount of water that discharges out from these springs is about 10 m3/s. If the elevation of the reservoir is below 398.00 m, then the possibilities for the appearance of water in Duboki do is negligible. In order for that to happen, the inflow should be more than 250 m3/s. The highest level of flood water (April 27, 1979, 424.87 m) was registered in a period when the level in the reservoir was 399.5 m, and inflow was 555 m3/s and, an extreme 646 m3/s the day before. If the inflow is less than 100 m3/s the floodwater in Duboki do doesn’t appear even elevation of reservoir is 400.00 m. In the winter of 2009/2010, unprecedented rainfall occurred as a result of two linked waves of extreme precipitation in the wider region of this part of the Dinarides. At the precipitation station in Gacko, from December 13. 2009 to Januray 13. 2010, 669.19 mm of rain was registered, followed by sudden melting of snow, so precipitation must have been greater than 700 mm. This is three times more than the average precipitation at the same station for the same period annually. It is 25% larger than the largest precipitation registered for that period. As a consequence of this precipitation, extreme values of GWL, discharge of springs and

estavelles, and flooding of Bilećko Polje were registered. The underground water level in the PB-1 piezometer rose to an elevation of 531 m (January 06. 2010), and the new flood in the polje reached the highest level registered so far, 426.55 m. Discharge on the springs along the northern rim of the polje started on January 06. 2010, and the flood lasted 11 days. During the flood period, inflows into the reservoir were between 370 m3/s and 529 m3/s, and maximum reservoir level was 398.65 m. During excavation of the Fatnica—Bileća tunnel, Duboki do was filled with excavated material, so the problem of its flooding is no longer relevant. A drainage tunnel was also dug between the lowest central part of Bilećko Polje and Bileća Reservoir, so the possibility of long-term flooding is reduced to a minimum. Inlet construction of the drainage tunnel is displayed in Fig. 5.12. With the construction of RPP Čapljina, flooding in Popovo Polje became significantly mitigated but the possibility of floods is not absolutely eliminated. This is confirmed by several floods of the downstream part of the polje that happened after RPP Čapljina become operational. One of the major floods after the construction of RPP Čapljina occurred in 1979. In addition to the enormous inflow of Trebišnjica, all springs and estavelles from the Gorica Dam to Strujići village in Popovo Polje reached

300

5 Influence and Consequences of Water Resources Projects

their maximums. A flood in Popovo Polje near Hutovo began on April 24, 1979 and reached its maximum on May 01 at 20: 00 h–243.27 m a.s.l. In the winter period of 2009/2010, the already mentioned largest flood occurred when RPP Čapljina was operational. The cause of the flood in Trebinjsko, Mokro and Popovo Polje was extreme precipitation in the whole region. Through the Gorica dam site to Trebinjsko Polje, flow reached between 327 and 365 m3/s; all temporary springs from the Gorica Dam to Dražin do reached previously unrecorded maximums. The operation of PP Dubrovnik at full capacity (89 m3/s) had an insignificant effect. Then, on January 11, 2010, the maximum level of 243.58 m a.s.l was registered at the Popovo Polje—Poljice gauging station. It is approximately 12 m above the Hutovo dam crest. That is 31 cm above the maximum level of floods in April/May1979. At that time, part of the polje in the area of Galičići village flooded. At this elevation of floodwater, numerous ponors around the perimeter of the polje are also activated (Žira, Provalija and numerous others). Under natural conditions, at this flood level, sinking was approx 155 m3/ s. With unprecedented maximum rainfall and inflow into Popovo Polje, it is obvious that under natural conditions consequences would have incomparably worse.

5.6.5

The Role of the Hydrosystem on Flood Mitigation

In several places in the previous chapters, it was pointed out that, under natural conditions, the karst of East Herzegovina characterizes hydrological extremes—droughts and floods. The periodic alternation of these extremes is a phenomenon for which the karst poljes of this region are known. This is why the old settlements were built on slopes above maximum flood levels. With the construction of the Trebišnjica Hydrosystem, the possibility of floods with the same intensity and frequency as natural conditions no longer exists, but local floods are not, nor can they ever be, completely eliminated. Because of intense urbanization of Trebinje, including accelerated construction of new infrastructural facilities in the polje, the flood problem is further current. Along with an increase in energy efficiency, one of the key strategic goals of the Trebišnjica Hydrosystem is to reduce the negative consequences of floods as much as possible. Experience acquired during the long-term operation of HET indicated the possibility that reservoirs and power plants in the system can adapt to active defense of the flood. This is why, in one part of the project ‘Management of reservoirs and hydroelectric power plants of Hydrosystem Trebišnjica’, special attention is focused on the formation of a management mechanism which would release only an allowed amount of

water, during extreme precipitation in the endangered part of the city. After a detailed analysis of the genesis of large water waves, an operational simulation model was made. The software is based on data about the current state of reservoirs and adopts the proposed values about the work regime very quickly, within a few seconds after information indicates a flow wave is forming. It creates a proposal for the most favorable management options, using minimum and maximum criteria of a moderate wave on the section through the Trebinje urban area. It is, in essence, a suboptimal solution for a simulated hydrological situation. It defines very clearly how aggregates should work and which dynamics should open the evacuation facilities on both dams. More important, the software shows how a mitigated wave will look in the section through the urban area of Trebinje, if the proposed management is immediately applied. Optimization analyzes have been done that have been translated into very transparent dispatch diagrams, whose use realizes a successful management compromise among three key users of HET: for energy, flood defense and water protection (Đorđević et al., 2012).

5.6.6

Estimation of Consequences of Partial Water Transfer from Catchments of Buna, Bunica and Bregava into Trebišnjica Catchment

Based on numerous geological, hydrogeological and hydrological works in the basins of the northwest part of East Herzegovina (Buna, Bunica and Bregava catchments) and processing of the collected data, the physics of the problem is defined in detail. This knowledge results in an unequivocal assessment that optimal regulation of the water regime of the entire region requires the transfer of part of the waters that belong to the Neretva catchment into the Trebišnjica catchment. It means that part of the waters of Nevesinjsko and Dabarsko polje catchments will be transferred into the catchment of the already operational part of the Trebišnjica Hydrosystem. This part of the Trebišnjica Hydrosystem is called Gornji horizonti (Upper Horizons, Fig. 4.9). It consists of a line of technologically connected structures, between which are the most important dams, Rilja and Pošćenje, the Zalomka and Nevesinje reservoirs, and the hydroelectric power plants, Nevesinje, Dabar and Bileća, with the possibility of transfer of part of the water from the catchment of Gatačko Polje. After power utilization transfers water in the existing and operational power plants (HPP Trebinje 1, HPP Trebinje 2 and RPP Čapljina), water will be returned to the Neretva River through the Krupa Dam, upstream from Metković. The reservoirs of Upper Horizons (Zalomka and Nevesinje)

5.6 Consequences of Water Regime Change

allow, in cases of extreme rainfall, mitigation of flood waves in the area of Stolac, Čapljina and Metković. In the dry period, flow of the Bregava River into Stolac and the Neretva River in Metković and downstream is increased. The Upper Horizons project plans to transfer about 30% (20 m3/s) of water of the Buna and Bregava catchments into the already operational part of the Trebišnjica Hydrosystem. It is ten times less than the average annual natural flow of the Neretva River in Mostar (197.4 m3/s). This is less than the least measured flows of the Neretva in Mostar (32 m3/s), and in the dry period there is no water for transfer in Upper Horizons. In this period, inflow into the Neretva from the area of Upper Horizons is also ten times smaller than Neretva discharge (Milanović et al., 2012). After construction of Upper Horizons, approximately 65% of water from Buna, Bunice and Bregava remains in a natural regime and itis not possible to influence them by applying any kind of man-made technical measures. These facts have beenchecked many times with different investigations and are confirmed by application of different mathematical models. In order to evaluate this impact, hydrological analyzes were performed under the assumption of complete “closure” of Biograd Ponor (Milićević, 1985). These analyzes show that, after the “closing” of the Biograd Ponor, decrease at a maximum by over 50% of average values, while minimal discharge will stay in the range of natural minimum discharges. According to M. Milićević’s calculation, which was made with daily values for a period of 6 years (1978–1983), average flow of the Bunica would be reduced from Q = 21.96 m3/s to the Q = 8.1 m3/s. In the 6-year analyzed period, the Biograd Ponor was active 213 days, and it swallows, on average, Qav = 13.6 m3/s. As a consequence of the “closure” of Biograd Ponor, the maximum discharge of Bunica would decrease from Q = 207.0 m3/s to Q = 86.2 m3/ s. This analysis shows the natural discharge of Bunica to be less than 4.00 m3/s and it is not possible to reduce discharge, regardless of prevention of sinking into Biograd Ponor. “Closing” the Biograd Ponor does not affect the water regime of Buna Spring because a physical relationship between them does not exist. In the analyzed period of 6 years, the yield of Buna was Qav = 25.5 m3/s. These analyzes showed that all enters in Nevesinjsko Polje give only 5.0 m3/s to Buna Spring. A small part of the Buna waters is a consequence of sinking along the Zalomka River, and the largest part of the water belongs to the huge intercatchment. Since the Upper Horizons project does not envisage the closing of large ponors in the northern part of Nevesinjsko Polje (Ždrijelo, Zlatac, Babova jama), it is obvious that only a negligible amount of water from the Buna catchment will be transferred. The considered area was modeled by three independent teams of experts, which resulted in the formation of three

301

different models: the model of J. Černi Institute, Belgrad; the K Sim model (Technical University, Athens) and the model of the Faculty of Civil Engineering, Belgrade. The general conclusions of all analyzes and models are the same and can be interpreted with an abbreviated version of the conclusions presented in the model of the Civil Engineerig Faculty, Belgarde: – The water regime on the Buna Spring does not disrupt, that is, the influence of water transfer is negligible. There will be no impact on low waters, because there is a large inter-catchment between the dam sites of Rilja and Pošćenje, which remains in its natural state, and a large inter-catchment of Nevesinjsko Polje to Buna, which is important for the formation of runoff in a low water period. – At Bunica Spring, there will be a reduction of high waters, even by more than 70%, which is very favorable from the point of view of the Neretva River water regime in a time of extreme high water. They reduce medium Bunica flow to less than 50%. However, low discharge remains undisturbed for durations greater than about 55%. In that range the duration curves in natural regimes practically coincides with duration curves after construction of the system. (Fig. 5.13). This means that, in this range of low waters, the civil structures on the Upper Horizons have no influence on the Bunica Spring water regime change.

All three models gave similar results for the consequences of converting waters to the water regime of the Bregava River: the impact on extremely high waters (over 50 m3/s) exists, but it is proportionately (percentage) small. Average flows (5–50 m3/s) are reduced, and the reduction percentage varies from model to model within the limits of 5% (10%) to 50%; flow regimes smaller than 5 m3/s are left unchanged. All themodels showed that the planned water system of Upper Horizons can harmoniously fit into the ecological and social environment. Also, the reservoirs that manage water regimes will improve ecological conditions in the wider area, including Trebišnjica discharge in the section through Trebinje (Đorđević & Dašić, 2011). During 2003/04, a study on the impact of water transfer through tunnel Fatničko Polje—Bileća Reservoir on the water regime of the Bregava River was done (Stanić & Dašić, 2005). Analyzes included the entire catchment area of the spring zone of the Bregava River, including part of the catchment of Trebišnjica springs which, in certain periods, affects the regime of the Bregava River (Fig. 5.14a). It is a simplified physical model with vertical water balance modeled by the UNSAT model, which is based on flow through the unsaturated environment, and flow in the horizontal direction is modeled as quasi-established circulation.

302

5 Influence and Consequences of Water Resources Projects

Fig. 5.13 The flow river duration curves at Bunica River, Malo Polje gauging station (Milanović et al., 2012)

By comparing the data obtained for natural conditions and conditions when there is a tunnel between Dabarsko and Fatničko Polje, it can be concluded that the operation of this tunnel slightly affects the waters of the Dabarsko and Fatničko Poljes, as well as the flows of Bregava springs. Flows smaller than 10 m3/s are completely unchanged (Fig. 5.14b). By including the Fatnica—Bileća tunnel in the operation, significant positive effects on flood levels can be observed in Dabarsko and Fatničko Poljes. However, the analyses show that, in the case of two tunnels flooding the polje, this is almost completely prevented if the Bileća Reservoir can accept inflows from the tunnel. When it comes to the Bregava springs, more significant influences appear for flows larger than 20 m3/s, that is, these flows (which are larger than the average annual flow) decrease by 15% to 29%. In contrast, flows of less than 10 m3/s remain completely unchanged.

5.7

Endemic Species Survival

Compared to non-karst terrains, the karst underground is rich with diverse fauna. In many cases this is endemic fauna. Construction of the facilities for HET released a flood in the large part of Popovo Polje, the Trebišnjica riverbed was blanketed by concrete, and many estavelles were closed. A greater number of estavelles along the edge of the polje were

disconnected from the river course, and the endemic fish gaovica lost the ability to complete their life cycle. Undoubtedly, survival of these endemic fish is endangered. A similar fate is waiting for the gaovica in other localities (Mokro Polje). By construction of hydropower facilities and urbanization in a large number of localities, the Proteus anguinus (human fish) is also endangered. Several natural karst shafts in the inner city core of Trebinje, in which the presence of Proteus is established, is covered by buildings and other structures. Its presence is still evident in a number of temporary springs and estavelles in Mokro, Trebinjsko and Popovo Poljes. Especially significant is the habitat of Proteus in Vjetrenica cave in Popovo Polje. By eliminating the flooding and isolation of the ponors Doljašnica and Crnulja from the Trebišnjica riverbed, the shell Congeria kusceri are endangered, as well as a worm— Marifugia cavatica (Fig. 3.23). Similarly, this can also be expected with deposits of Congeria kusceri in the Žira Ponor. In addition to the tourist importance and paleontological findings, the Vjetrenica cave is especially biologically interesting. Vjetrenica and some other speleological facilities in Popovo Polje (Doljašnica and Crnulja) were the subject of special speleo-biological analyses (Sket, 1983). This cave is a true reservation of endemic fauna and is not directly endangered by building facilities. This is why it is necessary to be under special protection against devastation. It is

5.7 Endemic Species Survival

303

Fig. 5.14 (a) Schematic presentation of the decomposed model of the Bregava springs catchment area (b) Flow graphs for the Bitunja Spring gauging station (Stanić & Dašić, 2005)

304

5 Influence and Consequences of Water Resources Projects

necessary to declare this cave as an endemic fauna reservation. A more detailed view of fauna is given in the subchapter 3.4, Fauna.

5.8

Induced Seismicity

The occurrence of induced seismicity as a consequence of the formation of artificial reservoirs has been known since the Hoover Dam was built in the USA in 1930, and this has been registered in the case of many deep reservoirs. During the filling of the Bileća Reservoir, induced seismicity as a consequence of sudden filling was registered, but it was also due to sudden saturation of karst underground. It was established that reservoirs affect a change of natural seismic characteristics in the observed radius of 75 km. Especially intense seismic activity was registered in a radius 20 km from the reservoir. The largest changes in seismic activities were registered in the first three filling cycles of reservoir and were characterized by the occurrence of a large number of low-energy earthquakes. The strongest earthquake was recorded in the period when a reservoir level of 400.00 m a. s.l. was reached for the first time. An earthquake of magnitude M = 4.5 released energy of E = 4.09 × 1016 erga. Induced seismicity was especially intense during the first cycle of filling, like that during discharge of the Bileća Reservoir. Residents in a village upstream of the dam felt a large number of weak earthquakes that caused light damage to facilities. During the first 6 years of reservoir operation, about 8000 weaker earthquakes (tremors) were registered. Analysis of the large number of registered earthquakes determined that during filling of the reservoir, energy is released through a large number of weaker earthquakes, and the most active areas are located near dams (Stojić, 1980). In order to monitor seismic activity, along with a seismograph at the Grančarevo Dam, six accelerographs and two seismoscopes were installed. It is known that heavy rainfall often causes seismic activity. Because of the specific karst porosity, extreme precipitation and fast saturation, this occurrence in karst manifests in the specific way. There was one occurrence a long time ago, registered by locals in a village above the Obod temporary spring in Fatničko Polje. Durung heavy rain, 10 to 30 h before discharge started, a slight shaking of the ground was felt and a rumble of “thunder” was heard. On the basis of these observations, a seismograph (vertical component) was placed above the Obod in 1970. These measurements confirmed that approximately 24 h before water appeared at the spring, there were ground tremors which were clearly written on the seismograph strips. Similar effects were registered by the locals in the initial phase of sudden filling of Vranjača i Jasikovac ponor zone in Malo Gatačko Polje. This type of induced seismicity is interpreted as a consequence of sudden filling of karst porosity and a fast increase

of the water table. Some of the air becomes trapped in channels and caverns in the form of “air pillows”. Due to strong pressure, the rising water squeezes out compressed air, with the effect of an explosion. Similar phenomena occur when the reservoir is suddenly filled. The consequences of these kinds of seismic activities are mostly local but can provoke light damage immediately nearby.

5.9

Eolian Erosion

The melioration of temporary flooded karst poljes caused a phenomenon that was not expected—aeolian erosion. In natural conditions, in the winter period, the karst poljes of East Herzegovina are flooded. In periods when the water receded for a short time, they were mostly covered with grass and other vegetation. Just after water withdrawal, local preparation for agriculture use began. When part of the Trebišnjica Hydrosystem was constructed, the largest part of Popovo Polje became liberated from the flood, and the fields were utilized for agricultural production. Under new conditions in winter, a large part of the fields were plowed and prepared for sowing. This is also a period with strong winds, primarily gales. Plowed surfaces are now notprotected by flood water or vegetation, grass. Strong winds lift huge amounts of plowed (shredded) soil. At certain moments, there is air with a reddish-brown color, a few tens of meters above the surface of the field. The color is from the large amount of particles that were transmitted and deposited on slopes on the edge of the polje. This appearance should be also taken into account in Fatničko Polje and partially in the case of Dabarsko Polje.

5.10

Importance of Water Potential of Southeast Dinarides

The area of East Herzegovina, together with part of Montenegro, especially the region of Boka Kotorska Bay, is endowed with exceptional water wealth. Average annual precipitation ranges between 1800 and 5000 mm. This is the region with the highest rainfall in the Mediterranean area. But since it is also among the most karstified areas in the world, a large part of these waters is unused. Infiltration exceeds 80%. Precipitation distribution is extremely uneven. About 70% of precipitation occurs in the wet period of the year, from October to April. The water flows underground and ends up in the sea through a series of large, concentrated springs and submarine springs, and the blue eye in the Neretva River delta. Differences between maximum and minimum flows of these springs are exceptionally high. In addition to its undoubted importance for energy and local water supply, this water also has undoubted importance for the part of the Mediterranean where the problems of water

References

supply become more and more acute. The water potential of the wider environment is significantly lower. The average annual rainfall in this part of the Mediterranean is between 410 and 1000 mm: Bari—580 mm, Cagliari—420 mm, Naples—1000 mm, Palermo—610 mm, Malta—550 mm and Athens—410 mm. The regional importance of the water potential of the Southeastern Dinarides was pointed out at the 32nd International Congress of Geologists in Florence, 2004, in the article “Water without boundary—Water resources potential in deep karst of South-Eastern Dinarides” and in the paper “Transboundary Aquifers in Karst—Source of Water Management and Political Problems, Case Study, SE Dinarides” Paris, in 2010. With the end of construction of the Trebišnjica Hydrosystem, the larger part of East Herzegovina water potential will be under control, with the possibility of offering a part of it to be used outside of this region. Efforts should also be made to tapp part of water that is now out of control, such as the Orjen waters. In karst conditions, this is a very complex and complicated problem that can only be solved with long-term and complex research. Since a deficit of highquality fresh water is increasingly present, it is clear that this potential cannot remain unused. In karst conditions, it will be necessary to find a balance between various water utilization possibilities for needs of water management, energy and to offer part of the water for market outside the region. Because of this, it is very important that this exceptional water potential and utilisation stay under permanent control and in permanent ownership of the local community, without the possibility of temporary or permanent possession by companies or individuals outside of the region. Future development of this region will depend, to a large extent, on the complete protection of this potential, both from the aspect of quality and from the aspect of utilization.

305

References Đorđević, B., & Dašić, T. (2011). Computation of environmental flows downstream from dams and river weirs (pp. 151–164). Đorđević, B., Dašić, T., & Sudar, N. (2012). Increase of the effectivenes of the reservoirs during the flood control–on the example of Trebišnjica hydrosystem. In Summary in English (Vol. 44, pp. 43–58). Milanović, P. (1986). Influence of the karst spring submergance on the karst aquifer regime. Journal of Hydrology, 84. Elsevier Science Publishers B.V. Milanović, P., Glišić, R., Đorđević, B., Dašić, T., & Sudar, N. (2012). Impacts of partial water re-routing from the Buna and Bregava catchments in the catchment of Trebišnjica River. In Summary in English Vodoprivreda (Vol. 44, pp. 3–23). Milanović, S., & Vasić, L. J. (2018). In S. Milanović & Z. Stevanović (Eds.), Hydrogeological characteristics of karst aquifer under conditions of reservoir and dam utilization–example of Bileća reservoir, Trebinje, BiH. Proceedings: KARST 2018, expect the unexpected. Centre for Karst hydrogeology. Milićević, M. (1976). Influence of man made reservoirs on change of natural floods upper karst poljes. Proccedings of Yugoslav-U.S. Symposium”Karst Hydrology and water resources” Institute for hydrotechnic. Milićević, M., & Krga, S. (1978). Influence of reservoirs in karst on microclime change. Conference on influence of man made reservoirs on environment. Yugoslav Commiittee of Lage dams. JKVB and HET. Milićević, M. (1985). Influence of construction large hydro structures on change the water regime in karst. Scientific Conference “Water and Karst”. Paviša, T. (1985). Adjustment of water regime in karst poljes–importance for food production–hydrotecnical part. Scientific Conference “Water and Karst”. Ramljak, P. (1978). Influence of construction of hydropower plants on littoral belt from Konavle to Stolac. Proccedings: Conference on influence of man made reservoirs on environment. Yugoslav Commiittee of Lage Dams. JKVB and HET. Sivrić, M. (1972). Role of hydropower company Trebišnjica to protect and save monuments of national hertage during construction of hydropower structures. In Publication “Arslanagića bridge”. HET. Sket, B. (1983). Importance of endangering of underground fauna in Popovo Polje and sugestions for its elementary protection. Proposals report. Institute for biolohy, University Ljubljana, pp. 1–22. Stanić, M., & Dašić, T. (2005). Modelling of water regime in karst. Vodoprivreda Vol. 37 br. 1–3, pp. 83–93. Stojić, P. (1980). Effects of reservoirs in karst areas on earthquakes. Hydrology papers, Colorado State University.

6

Chemistry and Water Quality

Ombla Spring

# The Author(s), under exclusive license to Springer Nature Switzerland AG 2023 P. Milanović, Karst of East Herzegovina and Dubrovnik Littoral, Cave and Karst Systems of the World, https://doi.org/10.1007/978-3-031-28120-4_6

307

308

6

6.1

Water Quality

6.1.1

History of Water Protection and Quality Control

The protection of water quality and water supply systems is regulated by laws implemented after construction of the first waterworks in this region. An example is the law for Dubrovnik water supply, which was brought about immediately after its construction—in 1443. According to this law, “if someone wash wool in the water canal, out of places assign for that, will be punished with 25 perper” (salary of master who performed supervision and repair of water supply system was 55 perper per year). Even stricter was the punishment for damaging water supply facilities: “Anyone who would open, break or clog channel for the water to spill, will be punished by the loss of the right hand” (Beretić, 1963). The law established the distance from the canal which must have all trees removed and vessels directed towards the canal. Severe fines and prison sentences were prescribed for everyone who polluted water. By law, from 1836, excavation of stone for a distance of 132 m from the spring and blasting at a distance of 380 m is forbidden. Chemical analyses of water and mud from the Mušnica River was carried out for the purpose of reclamation of Gatačko Polje. These analyses were performed in the Imperial-Royal Agricultural chemical experimental laboratories in Vienna between 1888 and 1890. With the beginning of construction of the water supply pipelines in certain urban areas, samples were taken for chemical analysis. This period is from the beginning to the middle of the twentieth century. Sampling is mostly concentrated in areas close to the springs. With the begining of work on the design and construction of the HET, more intensive and more systematic examination of water quality of the Trebišnjica River began (1960). The goal of these examinations, above all, was to determine the aggressiveness of water on the concrete. These tests have shown that at lower river flows, there is medium hard water, and at high water flows, it ranges between soft and hard water. In order to monitor changes in water chemistry at the coastal springs, which can arise as consequences of HET construction and a changed water regime, complete chemical analyses were performed on samples taken from 44 locations along the coastal belt, the Trebišnjica River and the Neretva valley. The affected area was from Konavosko Polje to the town of Metkovic during the period from 1961–1962. Samples were taken in different hydrological conditions: dry period (August–September), period of high water (February–March) and during medium water levels (May– June). Analysis of the underground water of Popovo Polje were exclusively composed of hydrocarbonate-calcium, whereas compounds HCO3 and Ca were predominate over

Chemistry and Water Quality

compounds Cl–Na or Mg–SO4. The water that flows from the springs has the same composition in Konavosko Polje and the Ombla Spring. The chemical composition of the waters between Ombla spring and Neretva are quite different. These are bicarbonate-calcium to magnesium-sulfate or chlorine-sodium. In the springs in the area of the sea coast, mineralization increased from 400 to 1000 mg/l. There were similar characteristics of the water in the springs along the lower course of the Neretva River (Mladenović, 1966). At approximately the same time, chemical analyses of water from springs and wells were carried out in the Bojišta area in Nevesinje Polje. These analyses were done for the needs of OGK (Basic Geological Map) Shit Nevesinje. Water was taken from the Stupine Spring and other springs (Andrić, 1965), as well as numerous analyses done for the article “Study of underground waters of Montenegro and East Herzegovina” (Torbarov & Radulović, 1965). To analyse chemical characteristics of water of the Ombla spring and its immediate catchments, water samples were taken from Ljubomirsko Polje (near Ždrijelovići ponor), from the Trebišnjica River near Kočela, the Reva shaft near Začula and from Ombla spring. The results of the analysis are shown in Table 6.1. According to bacteriological findings of the Ombla waterfalls in moderately bacteriologically polluted water, it should be permanently chlorinated for water supply needs. Bacteriological load is a frequent occurrence in karst catchment areas. The average number of germs is 280 and ranges from 10—innumerable. The average content of NVB coli bacteria is 1600, and their number in the water ranges widely, from 0 to 9600. About 40% are E coli. In order to assess the possibility of using environmental isotopes to determine directions of underground water, in November 1970 (high water stage) and May 1971 (low water stage), sampling was carried out on all significant flows and springs of East Herzegovina and Dubrovnik Littoral (23 locations). Sample analysis was carried out in Vienna at the United Nations International Atomic Energy Agency. Analysis was done on the content of δ18O and Tritium T.U. Analysis showed that the differences in the content of these isotopes in periods of high and low water are insignificant, and that this method is not applicable in the karst of this region due to the very high speeds of underground flows, that is, exceptionally fast turnover of underground water.

6.1.2

Results of Water Quality Analysis

Since 1974, systematic sampling has been done once or twice per year. These analyses are performed by the Institute for Public Health Care of Bosnia and Herzegovina in Sarajevo. From 1983, for these analyses is established laboratory for water chemistry as part (department) of Institute for Utility and Water Protection, Trebinje. It is done to control water

6.1 Water Quality

309

Table 6.1 Chemical properties of water in Ombla Spring catchment area

Evaporated rest (mg/l) Dry residue (mg/l) pH Carbonate hardness about dH Non-carbonated hardness about dH Aggressive CO2 _ (mg/l) Belonging CO2 _ (mg/l) Oxygen (mg/l) Oxygen demand (mg/l) H2S (mg/l) Nitrates NO3 (mg/l) Chlorides cl (mg/l) Sulfates SO4 (mg/l) Phosphates PO4 (mg/l) Hydrocarbons HCO3 mg/l Carbonates CO3 Calcium Approx (mg/l) Magnesium mg (mg/l) Sodium on the (mg/l) Ammonia NH4 (mg/l)

Ombla 162–253 89–173 7.1–7.8 8.1–12.1 0.1–0.7 0–2.42 5.7–7.6 8.9–9.5 0–1.84 0 0–5.4 6–45 7.5–15 0–0.04 117–195 0 50–54.5 6.9–8.4 4.5–9.4 0

quality of the river and spring water of the East Herzegovina catchments. In the past, about 1200 analyses were done and were obtained across 30,000 parameters (Mrkonja, 2004). Some of these parameters are presented in Tables 6.2 and 6.3. In the winter period of 1981/82 (high water), chemical analyses of water were performed at a large number of springs along the Dubrovnik Littoral. The analyses were carried out by the Division of Analytical Chemistry of the technical faculty at the University of Zagreb. These results are displayed in Table 6.4. In the period 1997–2015, samples were taken from 50 locations in the Trebišnjica catchment and analyses were performed that included: main ions, water and air temperature, color, turbidity, smell, taste, pH, dissolved oxygen, bound oxygen, BOD5, HPK (measured across KmNO4), CO2, electric conductivity (EC), TDS, hardness, alkalinity and many other required parameters. Analyses (multivariate statistician analysis and hierarchical cluster analysis) were done to define the chemical characteristics and quality of water in the Trebišnjica catchment. These analyses were confirmed with previous results of hydrochemical research regarding the crucial influence of mineralogical composition of soil on the chemical characteristics of water locally, and also regarding anthropogenic influences on the quality of water, that is, biological pollution (Banjak, 2018).

6.1.3

Turbidity

It is known that the waters of karst springs become turbid after intense rainfall. This occurrence is registered in many

Reva Začula 280 160 7.6 10.80 0.1 About 14,18 7.4 0.4 0 5.2 7.64 7,8 0.1 235 0 74.5 1.74 9.8 0

Kočela Trebišnjica 137 83 7.9 6.72 0.44 0 3.5 9.8 0.6 0 4.06 5.56 2.6 0.026 146 0 39,27 7.15 2.7 0

Ljubomir 190 115 8.1 9.69 0.38 0 9.6 10,13 0.10 0 1.15 4.45 5.8 0.026 198 0 47.74 14.52 3,3 0

springs of East Herzegovina and Dubrovnik Littoral and is one of the more serious problems of tapped springs in karst. In some cases, turbidity is so high, it makes the water unusable for drinking for a short time. Turbidity is a consequence of large amounts of undissolved sediments in the karst underground, created by the process of erosion and tectonic disintegration of rocks and by transporting suspended and partly bed-load sediments. Sediments belonging to the smallest (0.002 mm) and colloidal (0.0002 mm) fraction are, in the area of the southeastern Dinarides, most often of glaciogenic origin and were transported by fluvioglacial flows. In a period when speed is reduced, or there is water flow cessation, the process of sedimentation takes place, but when turbulent flows restart, part of the water is transported to the place of discharge. When this happens in catchment areas that contain karst poljes, during floods, large amounts of suspended material are transported into the underground. Groller calculated that, during the flood of Popovo Polje in 1889, water contained one liter, 0.132 g, of colloidal material, i.e., 18,500 m3 in the accumulated flood. Part of that material was sediment on the polje surface, but an even larger part of the water was brought into the underground along the karstified Trebišnjica riverbed and through numerous ponors outside the riverbed and were transported by underground flows to discharge places. Along this flow, a large part of these sediments precipitated into caverns and channels. If the flow of the Trebišnjice and polje flooding lasted continuously for over 200 days, and discharge of turbid water at the springs was sporadic and short-lived, with a duration of 2 to 10 days, and if it happened exclusively during sudden and heavy rainfall in the wider hinterland of the spring, the question arises of what happens to the

310

6

Chemistry and Water Quality

Table 6.2 Chemical properties of water in Trebišnjica River catchment area in 1996 and in 2002 (Mrkonja, 2004) Parameters Temperature water ° C pH Consumption KMnO4 mgO2 /l Dissolved oxygen mgO2 /l Saturation oxygen % BOD5 mgO2 /l CO2_mg/l Chlorides mgCl/l Calcium mgCaO/l Magnesium mgMgO/l Alkalinity about dH Total hardness about dH Permanent hardness about dH Evaporated rest mg/l Ammonia mgN/l Nitrites mgN/l Sulfates mgSO2- /l 4 3-Phosphates mgPO4 /l Iron mgFe/l Manganese mgMn/l

Srđevići 7.0–21.4 7.8–12.5 8.5 1.47–3.99 2.90 6.4–13.3 9.1 66.8–116.8 89.9 0.56–2.64 1.44 0.0–17.5 6.1 3.0–27.8 12.6 59.2–105.2 85.9 0.0–28.2 7.0 3.9–10.3 8.2 7.6–10.9 9.6 0.22–4.14 1.42 193–291 241.5 0.05–0.5 0.1 0.005–0.05 0.01 21.1–67.2 41.8 0.03 0.06–0.1 0.07