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Reservoir sedimentation: assessment and environmental controls
 9781138493636, 1138493635, 9781351027502

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Reservoir Sedimentation

Reservoir Sedimentation Assessment and Environmental Controls

Kumkum Bhattacharyya Vijay P. Singh

CRC Press Taylor & Francis Group 6000 Broken Sound Parkway NW, Suite 300 Boca Raton, FL 33487-2742 © 2019 by Taylor & Francis Group, LLC CRC Press is an imprint of Taylor & Francis Group, an Informa business No claim to original U.S. Government works Printed on acid-free paper International Standard Book Number-13: 978-1-138-49363-6 (Hardback) International Standard Book Number-13: 978-1-351-02750-2 (eBook) This book contains information obtained from authentic and highly regarded sources. Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. Except as permitted under U.S. Copyright Law, no part of this book may be reprinted, reproduced, transmitted, or utilized in any form by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying, microfilming, and recording, or in any information storage or retrieval system, without written permission from the publishers. For permission to photocopy or use material electronically from this work, please access www.copyright. com (http://www.copyright.com/) or contact the Copyright Clearance Center, Inc. (CCC), 222 Rosewood Drive, Danvers, MA 01923, 978-750-8400. CCC is a not-for-profit organization that provides licenses and registration for a variety of users. For organizations that have been granted a photocopy license by the CCC, a separate system of payment has been arranged. Trademark Notice: Product or corporate names may be trademarks or registered trademarks, and are used only for identification and explanation without intent to infringe. Library of Congress Cataloging-in-Publication Data Names: Bhattacharyya, Kumkum, author. | Singh, V. P. (Vijay P.), author. Title: Reservoir sedimentation / Kumkum Bhattacharyya and Vijay P. Singh. Description: Boca Raton : Taylor & Francis, a CRC title, part of the Taylor & Francis imprint, a member of the Taylor & Francis Group, the academic division of T&F Informa, plc, 2018. | Includes bibliographical references. Identifiers: LCCN 2018010552| ISBN 9781138493636 (hardback : acid-free paper) | ISBN 9781351027502 (e-book) Subjects: LCSH: Reservoir sedimentation. Classification: LCC TD396 .B345 2018 | DDC 627/.86--dc23 LC record available at https://lccn.loc.gov/2018010552 Visit the Taylor & Francis Web site at http://www.taylorandfrancis.com and the CRC Press Web site at http://www.crcpress.com

Dedication KB: Late parents (Shri. Mohini Mohan Bhattacharyya and Smt. Jyotirmoyee Bhattacharyya), mentor Manjusri Basu, husband Raj Swamy, my family and friends. VPS: Wife Anita, son Vinay, daughter Arti, daughter-in-law Sonali, son-in-law Vamsi, and grandsons Ronin, Kayden, and Davin.

Contents Preface.......................................................................................................................xi Acknowledgments .................................................................................................... xv Authors ...................................................................................................................xvii List of Abbreviations...............................................................................................xix Chapter 1

Introduction ..........................................................................................1 1.1 1.2 1.3 1.4

Background .............................................................................1 Global Water Resources ..........................................................5 Development of River Basin Organizations .......................... 12 Development of Water Resources through Creating and Maintaining Dams/Reservoirs .............................................. 12 1.5 Geographical Scenario of India ............................................ 13 1.5.1 Physiographic Regions ............................................ 14 1.5.2 Geology ................................................................... 15 1.5.3 Climate .................................................................... 17 1.5.3.1 Precipitation ............................................. 18 1.5.4 Soils ......................................................................... 23 1.5.5 River Systems ..........................................................25 1.5.6 Distribution of Water Resources .............................28 1.5.7 River Systems and Associated Flood Problems ...... 30 1.5.8 Biodiversity ............................................................. 30 1.6 Dam/Reservoir Scenario ....................................................... 32 1.6.1 Classification of Reservoirs ..................................... 35 1.6.2 Effects of Dams and Reservoirs .............................. 38 1.7 Rate of Sedimentation: Need for Assessment ....................... 42 1.8 Reservoir Sustainability ........................................................ 43 1.9 Scope and Organization ........................................................44 1.10 The Organization of This Book ............................................44 References .......................................................................................... 45 Chapter 2

Land Degradation and Sediment Fluxes in the Anthropocene .......... 55 2.1 2.2 2.3 2.4

Land Degradation Due to Human Activity ........................... 55 2.1.1 Land Degradation .................................................... 56 2.1.2 Extent and Causes of Soil Degradation by Region .... 62 Climate Change and Changing Regional Sediment Transport Pattern...................................................................66 Global Sediment Yield .......................................................... 69 Global Sediment Flux Since the Late Jurassic (In Pre-Human Conditions)................................................... 72

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2.5

Role of Dams in Reducing Sediment Fluxes ........................ 73 2.5.1 Sediment Flux of Indian Subcontinent: Past and Present .............................................................. 78 2.5.1.1 Peninsular Rivers ..................................... 78 2.5.2 Sediment Flux of Indian Subcontinent: Past and Present .............................................................. 82 2.5.2.1 Extra Peninsular Rivers (GangaBrahmaputra and Indus)........................... 82 2.5.3 Sediment Flux of Large East and Southeast Asian Rivers ............................................................ 83 2.6 Conclusion ............................................................................. 85 References .......................................................................................... 85 Chapter 3

Sedimentation in Reservoir and Measurement .................................. 95 3.1 3.2 3.3 3.4 3.5 3.6

Sedimentation in Reservoir and Its Impact ........................... 95 Sediment Transport in Fluvial Systems ................................96 Sedimentation Process ..........................................................97 Sedimentation Planning-Life of Reservoir............................99 Distribution of Sediment ..................................................... 100 Hydrologic Variability and Reservoir Hydrologic Capacity .............................................................................102 3.7 Reservoir Sedimentation and Storage Loss......................... 104 3.8 Sediment Monitoring .......................................................... 107 3.9 Measurement Techniques of Sedimentation ....................... 107 3.9.1 Stream Flow Analysis ........................................... 107 3.9.2 Capacity Survey .................................................... 108 3.9.2.1 Hydrographical Surveys......................... 108 3.9.3 Modern Techniques ............................................... 109 3.9.3.1 Hi-tech Systems ..................................... 109 3.9.3.2 Remote Sensing...................................... 109 3.10 Status of Reservoir Sedimentation Surveys ........................ 111 3.11 Study Area ........................................................................... 111 3.12 Data Sources........................................................................ 112 3.13 Methodology ....................................................................... 113 References ........................................................................................ 114 Chapter 4

Reservoir Sedimentation Rate .......................................................... 121 4.1 4.2 4.3 4.4

Sedimentation Surveys of Reservoirs .................................... 121 Observed Rates of Sedimentation ......................................... 121 Region-Wise Sedimentation Rates ........................................ 125 Characteristics of Sedimentation........................................... 126 4.4.1 Sediment Yield Maps ............................................ 128 4.4.2 Estimation of Loss of Storage in Reservoirs ......... 129 4.4.3 Reduction in Sedimentation Rate .......................... 132

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Assessment of Sedimentation Characteristics Using a Satellite Remote Sensing Approach .................................... 139 4.6 Relationship between Catchment Area of Reservoir and Average Annual Rate of Sedimentation .............................. 146 4.7 Hot Spot Analysis ................................................................ 149 4.8 Sediment Deposition in a Reservoir .................................... 152 4.9 Distribution of Sediment in Reservoirs ............................... 153 4.10 Density of Deposited Sediment in Reservoirs .................... 156 4.11 Analysis of Deposited Sediment ......................................... 157 4.12 Estimated Life of Reservoirs ............................................... 157 References ........................................................................................ 159 Chapter 5

Sediment Yield ................................................................................. 163 5.1

Sediment Yield .................................................................... 163 5.1.1 Sediment Yield Map .............................................. 164 5.2 Proneness of Hilly Areas to Soil Erosion and Faster Rate of Reservoir Sedimentation ........................................ 164 5.3 Relationship of Land Use and Land Cover Change to Reservoir Sedimentation ..................................................... 169 5.4 Catchment Size and Sediment Yield ................................... 176 5.5 Area-Wise Soil Erosion Risk............................................... 186 5.6 Precipitation and Sediment Yield ........................................ 186 5.7 Potential Effects of Global Climate Change on Sediment Yield .................................................................... 188 References ........................................................................................ 191 Chapter 6

Reservoir Sediment Management Strategies.................................... 195 6.1

6.2

Sediment Management Strategies ....................................... 195 6.1.1 Reduce Sediment Yield from Upstream Watershed .............................................................. 199 6.1.1.1 Soil Erosion Control............................... 199 6.1.1.2 Watershed Approach ..............................202 6.1.1.3 Participatory Resource Conservation and Management—Case Studies ...........206 6.1.1.4 Construction of Upstream Dams ...........208 6.1.2 Sediment Routing around or through Reservoirs ............................................................211 6.1.3 Recover, Increase, or Reallocate Reservoir Volume .................................................................. 216 6.1.4 Dam Removal ........................................................ 219 6.1.5 No Action .............................................................. 222 Sustainable Sediment Management .................................... 222

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Economical Model: Reservoir Conservation and Life Cycle Approach for Sustainable Management of Large Hydro Projects, RESCON (REServoir CONservation) Approach ............................................................................... 223 6.4 Environmental Considerations .............................................. 226 6.5 Implementation of Sediment Management Plan ................... 227 6.5.1 Monitor and Revise Plan as Necessary .................... 227 References ........................................................................................ 228 Chapter 7

Epilogue............................................................................................ 237 7.1 7.2 7.3 7.4

Characteristics of Sedimentation in Indian Reservoirs ......... 237 Sustainable Freshwater Resources.........................................240 Storage Requirement ............................................................. 242 Changing Climate, Changing Environment, and Robust Infrastructure ......................................................................... 242 7.5 Holistic Approach towards Water Resource Management .... 245 7.6 Twofold Nature of Storage ..................................................... 247 7.7 Natural Resource Economics ................................................248 7.8 Conclusion ............................................................................. 252 References ........................................................................................ 252 Appendices ............................................................................................................ 257 Image and Data Source Credits ......................................................................... 305 Index ......................................................................................................................307

Preface High rates of sedimentation in many reservoirs directly affect the performance of dams, leading to the reduction in the storage capacity of the reservoir, which, in turn, significantly impairs the function and sustainability of the dam and the reservoir. Sedimentation is a serious problem worldwide and will be a major concern in the coming decades, which calls for careful consideration. Proper allocation and management of water in a reservoir, therefore, demand periodic assessment of its capacity, which has become a significant issue for planners, designers, and operators of dams to consider very early in the decision-making and design processes. Per capita water resources have been reduced significantly due to rising population, poor water management, increasing water demand, and climate change. Studies project that the phenomenon of climate change will affect water resources significantly by changing mean annual river flows and hydrologic variability, thereby triggering more extreme droughts and floods. To adopt judicious water resources management strategies, it therefore becomes necessary to understand global water resources trends and various consequences of reservoir sedimentation due to sediment trapping and the related impact on the environment. Among various strategies, one is the assessment of sedimentation rates in reservoirs to determine their actual storage capacities and capacity reduction rates through time. It is also significant to recognize the importance of creating and maintaining reservoir storage by facilitating rapid identification of reservoir sediment management strategies that are technically sound and economically optimal to prolong the operational life of dams and reservoirs. This book, therefore, is a response to the need for reservoir management. Its purpose is to provide information for policy makers to empower them to manage dams and reservoirs and ensure the sustainability of water resources. This information can provide insight and lays the groundwork for retrospection of the effects of anthropogenic intervention in the natural environment through dams and reservoirs in the Anthropocene. Dams and reservoirs have played a vital role in the socioeconomic development of societies across the world. However, these hydraulic structures also have had a negative side. They trap sediment and starve downstream river reaches and areas of much-needed sediment. The trapped sediment leads to reservoir sedimentation which, in turn, reduces storage capacity, threatening the sustainability of water supply and hydropower generation. The first chapter discusses the sedimentation issues in general with an emphasis on sedimentation issues in India. Major ancient civilizations were hydraulic civilizations that developed in the flood plains, which provided fertile lands for farming and raising cattle. The activities of growing populations have subjected rivers and their flood plains to increasing mistreatment, resulting in several challenging situations due to the tremendous pressure exerted on limited natural resources. These activities have been beneficial to the population; however, long-term costs to natural resources are substantial and, at a century or greater scale, these costs may even surpass the benefits. The costs are the decline of freshwater resources, degradation and collapse of land, subsidence and dwindling xi

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of delta regions, loss of biodiversity, hazards to health, and loss of coastal lands. The second chapter discusses land degradation, sediment trapping by dams, and reduced sediment fluxes to the world’s oceans resulting from human activities as well as global sediment flux since the late Jurassic period (in pre-human conditions). One of the key factors that determines the reservoir design life is sedimentation which, in turn, depends on land use and land management practices in the upstream watershed. The third chapter reviews the literature related to sedimentation and discusses the process and impact of sedimentation and measurement of sedimentation. The chapter defines the study area, the data gathering process, the sources of data, and the methodology of study. Organizations build reservoirs with a great deal of planning and engineering expertise that requires huge investments. It is, therefore, vital that the reservoirs serve the intended purposes for the duration of the design life. The fourth chapter discusses reservoir sedimentation characteristics, sedimentation hot spots, and the relationship between reservoir catchment area and average annual rate of sedimentation. One of the key factors affecting reservoir sedimentation is the sediment yield, which varies widely both spatially and temporally and often much less than the erosion rate within the same drainage basin. A multitude of factors affect sediment yield, such as rainfall and soil characteristics, soil management, topography, catchment size, surface runoff, sediment features, channel hydraulics, vegetation, land use and land cover, construction, and anthropogenic disturbance. Studies also cite climate change as a potential factor. The fifth chapter discusses the effect of these factors on reservoir sedimentation in relation to several reservoirs specifically in India as well as other countries. The sixth chapter discusses the possible use of various strategies to accomplish effective sediment management. Effective sediment management strategies require an integrated approach to adopt appropriate soil conservation measures in the catchment so that sediment inflow to the reservoir is within acceptable limits. Likewise, it is also important to ensure that sediment deposition in the reservoir occurs within acceptable limits. The chapter discusses different sediment management techniques, such as catchment erosion control and upstream sediment trapping, rerouting sediment through drawdown operations, off-stream reservoirs, sediment bypass, or periodic removal of deposited sediment through dredging, excavation, or hydraulic flushing, which are available for sediment management for converting sedimented reservoirs into sustainable resources. The RESCON (REServoir CONservation) approach, which uses the life-cycle management approach instead of the design life approach, acknowledges the need for intergenerational equity and promotes policy makers’ awareness of the importance of reservoir conservation. The previous chapters discuss land degradation that leads to an increase in watershed sediment yield, which then feeds into a reservoir and causes sedimentation. The rate of sedimentation impacts reservoir storage and design life and in turn the sustainability of freshwater resources needed for meeting reservoir design objectives. Reservoir sedimentation thus plays a fundamental role in the need to develop measures for sediment management and in turn to develop approaches for sustainable water resources management and infrastructure development. These measures must take into consideration climate change and changes in the environment and

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ecosystem which are likely to accelerate in the decades ahead. The seventh chapter provides a snapshot of these issues. This book will be useful for graduate students and faculty members working in reservoir sedimentation; for watershed managers and environmental scientists concerned with the environmental impacts of hydraulic structures; for reservoir managers and river valley corporations dealing with reservoir operations; and for those who are interested in reservoir planning and design. Kumkum Bhattacharyya Seattle, Washington Vijay, P. Singh College Station, Texas

Acknowledgments Kumkum Bhattacharyya expresses her sincere gratitude to Professor G. M. Kondolf (University of California, Berkeley) for providing her with an opportunity to work on reservoirs in California. She is also thankful to T. Minear (USGS), who was working on reservoirs in California. She gives special thanks to them for the generosity of imparting ideas and their influence on this work has been perhaps deeper and more significant than that of any others. The present study began with a literature review on reservoirs in California. She is also indebted to B. Greiman, R. Ferrari, T. Yang, (U.S. Bureau of Reclamation), R. Volpe, (Santa Clara Valley Water District), and K. Buer, (California Department of Water Resources, Red Bluff, California) for providing data and information on the reservoirs of California. She is deeply appreciative of Dr. R. Stallard (U.S. Geological Survey) who provided the following report on reservoir sedimentation in India: CWC (Central Water Commission). 2001. Compendium on Silting of Reservoirs in India, Reservoir Sedimentation Directorate, CWC, Government of India, New Delhi. The updated version of this report, published in 2015, is available online. She is also most grateful to the staff of ESRI (Redlands, California), CWC (India), WRIS (India), NATMO (India), and DVC (India) for providing her with the topographic maps, aerial photos, data, and information. She is thankful to Ms. Linda Vida, Director and other librarians, Water Resources Center Archive, and all librarians of the University of California, Berkeley, and librarians of King County Libraries and especially Federal Way Regional Library of Western Washington for their assistance. She is grateful to Professor D. Montgomery and H. Greenberg of the University of Washington, Seattle, for extending the facilities of Spatial Analysis Lab. Harvey, as usual, always helpful in providing GIS data sets and answering GIS-related questions. She benefitted from discussing several concepts of reservoir sedimentation with DVC engineers, especially B. Goswami and D. Chaudhury. She is very grateful to them. She also wants to express her gratitude to her best mentor, Manjusri Basu, formerly Reader, University of Burdwan, India, who inculcated in her an interest in fluvial geomorphology and coupled human and fluvial system. She is also very indebted to Michael, J. Wiley (formerly Professor, University of Michigan), Prabhat Kumar Sen (late Professor, University of Burdwan), Dr. Asim Kumar Goswami (Research officer, NATMO) and Reds Wolman (late Professor, Johns Hopkins University), for their encouragement. She acknowledges with deep appreciation to P. G. Griffiths (USGS), Shi Qi, (Beijing Forestry University, Beijing, China), R. Srivastava (CWC, India), D. Sanjeev (Institute of Technology, Mumbai, India), H. Gupta (Osmania University, Hyderabad, India), D. Chaudhuri (DVC, Kolkata, India), for providing resources, data and photographs. She offers a special thanks to Dr. S. Dutta for providing her valuable insight while fine tuning the manuscript at the very initial stage. She is also very grateful to Dr. A. Sarkar for her help in editing a shapefile, reproducing a map, creating a table and an appendix. She is also thankful to M. Dey for creating an appendix. She is also greatly indebted to Swami Chetanananda, Minister xv

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of Vedanta Society of St. Louis for checking references of ancient Indian literature pieces, used in the present study. Thanks, and admiration go to the many authors, researchers and scientists whose published research has enriched this study. Special thanks go to her late parents, and to family, friends, and relatives for their continuous support and affection. She has received much needed support and inspiration from her sisters. Finally, she gratefully acknowledges the continuous encouragement, ongoing patience, support and affection from her husband, Raj Swamy. Vijay P. Singh expresses his sincere gratitude to his family, his wife Anita, son Vinay, daughter Arti, daughter-in-law Sonali, son-in-law Vamsi, and grandsons Ronin, Kayden, and Davin for their encouragement, support, and affection. The authors especially thank the dynamic team of Ariel St. Felix, Joseph Clements, Erin Broemel, Iris Fahrer, Florence Kizza (CRC Press & Routledge | Taylor & Francis Group) and Raina Mohammed, R. Visvanathan, and John Shannon (Datamatics) for their continuous support, endless patience, and kindness.

Authors Dr. Kumkum Bhattacharyya earned her PhD degree in 2000 from the University of Burdwan, India, followed by post-doctoral research at the University of California, Berkeley (2002–2003), where she worked on sediment management in aging reservoirs. She has been involved in research on “Age-Old Dance between Humans and Rivers” for over two decades and has been continuously working on several projects, including “The Humans Transforming the Fluvial Landscape into Hybrid Landscape”, “Advancing Watershed Sustainability”, and “Participatory Resource Management involving Riparian Communities”. Her PhD thesis entitled “Applied Geomorphological Study in a Controlled Tropical River—The case of the Damodar River between Panchet Reservoir and Falta” was examined by M. Gordon Wolman, (late professor), from Johns Hopkins University. She published a book based on her Ph.D research which is entitled “The Lower Domodar River, India: Understanding the Human Role in Changing Fluvial Environment” in 2011 by Springer. She has contributed in prioritizing environmental cleanup activities at Washington State Department of Ecology, contributed to the development of the “Oregon Explorer Wetland Portal” and helped develop a statewide GIS database of wetlands for Oregon. As Research Associate, she has also assisted M.J. Wiley (Former Roosevelt Professor of Ecosystem Management, University of Michigan) on a project “Geomorphic-Fisheries Interactions in the lower Ganga River”. As a Visiting Assistant Professor, she has contributed to Geography/GIS Program at the University of Central Arkansas (UCA), Conway, Arkansas and at Eastern Oregon University, La Grande, Oregon during the academic years between 2012 and 2016. She has also taught at Eastern Michigan University, Saginaw Valley State University (SVSU), in Michigan State as well as Highline Community College in Washington State during the academic years between 2005 and 2014. After returning to Washington State, she is presently involved with a teaching institution. Professor Vijay P. Singh is a University Distinguished Professor, a Regents Professor, and the inaugural holder of the Caroline and William N. Lehrer Distinguished Chair in Water Engineering in the Department of Biological and Agricultural Engineering and Zachry Department of Civil Engineering at Texas A&M University. He earned his BS, MS, PhD, and DSc degrees in engineering. He is a registered professional engineer, a registered professional hydrologist, and an Honorary Diplomate of the American Academy of Water Resources Engineers. He has published more than 1,054 journal articles; 28 textbooks; 67 edited reference books, including the Encyclopedia of Snow, Ice and Glaciers, and the Handbook of Applied Hydrology; 104 book chapters; 314 conference papers; and 72 technical reports in the areas of hydrology, groundwater, hydraulics, irrigation engineering, environmental engineering, and water resources. For his scientific contributions to the development and management of water resources and promoting the cause of conservation and sustainable use, he has received more than 90 national and international awards and xvii

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numerous honors, including the Arid Lands Hydraulic Engineering Award, Ven Te Chow Award, Richard R. Torrens Award, Norman Medal, and EWRI Lifetime Achievement Award from the American Society of Civil Engineers; Ray K. Linsley Award and Founder’s Award from the American Institute of Hydrology; Crystal Drop Award and Ven Te Chow Memorial Award from the International Water Resources Association; and the Outstanding Distinguished Scientist Award from Sigma Xi. He has received three honorary doctorates. He is a Distinguished Member of ASCE, and a fellow of EWRI, AWRA, IWRS, ISAE, IASWC, and IE and holds membership in 16 additional professional associations. He is a fellow/member of 10 international science/engineering academies. He has served as President and Senior Vice President of the American Institute of Hydrology (AIH). Currently he is editorin-chief of two book series and three journals and serves on editorial boards of 20 other journals.

List of Abbreviations b m3 CA CBIP km3 m3 m3/s CWC DVC ESRI F.R.L g GIS GSI ha ha m I & W.Dept km m M m3 MDDL mg Mha mm MRO M.S.L NA NATMO km2 SPR t K m3 India-WRIS Yr

Billion cubic meters Catchment Area Central Board of Irrigation and Power Cubic kilometer Cubic meter Cubic meter per second Central Water Commission Damodar Valley Corporation Environmental System Research Institute Full Reservoir Level Gram Geographic Information Systems Geological Survey of India Hectare Hectare meter Irrigation and Waterways Department Kilometer Meter Million cubic meters Minimum Draw Down Level Milligram Million hectares Millimeter Manager Reservoir Operation Mean sea level Not available National Atlas and Thematic Mapping Organization Square kilometer Sediment Production Rate Ton Thousand cubic meter Water Resources Information System Year

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1 1.1

Introduction

BACKGROUND

Storage reservoirs and dams have played an important role in the development and management of water resources and will continue to do so in the foreseeable future. Engineers design these structures to serve various purposes, such as storage of scarce water and subsequent distribution, flood control, water storage for irrigation, hydropower generation, navigation, municipal water supply, recreation, fisheries, and ecological and environmental health (Veltrop 1992; NIH 1997–98; Morris & Fan 1998; CWC 2001, 2015; Jain & Singh 2003; Garde 2006; ICOLD 2009; Annandale 2013, 2014; Annandale et al. 2016; Ho et al. 2017). Dams and reservoirs control floods and reduce downstream flood damage by temporarily storing a large part of the flood runoff. But they also influence sediment transport through river systems, thus permanently affecting flow variability downstream (Kondolf et al. 2014). Reservoir sedimentation due to dam construction leads to diminution of storage capacity which, in turn, can significantly weaken the ability of a dam to perform to its design objectives (Murthy 1995; Morris & Fan 1998; Jain & Singh 2002; Graf et al. 2010; Yuan et al. 2015; Bhattacharyya 2016a). High rates of sedimentation in many reservoirs and increased concern for long-term sustainability have highlighted the significance of reservoir sedimentation (ICOLD 2009). Reservoir sedimentation is a universal phenomenon which scientists now regard as one of the most serious environmental menaces of modern times (Jain & Kothyari 2000). A reservoir obtains inflow from major rivers because its position is generally towards the end of a large watershed (Jørgenson 2005). Reservoirs that have a shorter resident time, but a much larger watershed, can be more challenging to regulate (Randolph 2004). The life of a reservoir starts diminishing soon after an agency decommissions it due to continuous deposition of sediment eroded or splashed from all parts of the watershed. Proper allocation and management of water in a reservoir, therefore, calls for periodic assessment of its capacity. Accurate surveys of reservoir capacity are important to assess the pattern of sedimentation for an optimum reservoir operation schedule (Thomas et  al. 2009). According to the statistics of the International Commission on Large Dams (ICOLD), as of 2017, globally there are approximately 58,519 large dams with countless smaller ones. The Global Reservoir and Dam (GRanD) database comprises information regarding 6,862 dams and their associated reservoirs with a cumulative storage capacity of 6,197  km3 (Figure 1.1). The largest combined volumes are concentrated in Canada, Russia, the United States, Brazil, and China. It is estimated that there are about 16.7 million reservoirs larger than 0.01 ha with a combined storage capacity of about 8,070 km3 which may exist worldwide (Lehner et al. 2011; Miao et al. 2015). The projection is that, at an annual reservoir sedimentation rate of about 31 km3 (discounting new storage created after 2004), the global reservoir storage capacity will decrease by about half by 2100 (Sumi et al. 2004). Reports indicate that the global net reservoir storage has been decreasing because rates of sedimentation are surpassing rates of new 1

FIGURE 1.1 Global Reservoir and Dam (GRanD) Database. GRanD contains 6,862 records of reservoirs and their associated dams with a cumulative storage capacity of 6,197 km 3. (Source: http://www.gwsp.org/products/grand-database/global-reservoir-and-dam-grand-databaseproject.html, Digital Water Atlas at Global Water System Project (GWSP), Lehner et al., 2011, ArcGIS online resources).

2 Reservoir Sedimentation

Introduction

3

storage construction. According to Annandale (2013), with increasing demands for water storage and fewer feasible and economically justifiable sites available for new reservoirs, the loss of capacity in existing reservoirs threatens the sustainability of water supply. The rate of global sedimentation is about 0.8 percent per year (Basson 2008; ICOLD 2009) and sedimentation rates worldwide exceed the rate of storage capacity of new dams. Generally, the global annual reservoir storage loss due to sedimentation varies from 0.1 percent to 2.3 percent, with an average annual world storage loss of about 1 percent (Liu et al. 2002; Walling 2006). The average rate of more than 1 percent storage loss by reservoirs in South Asia (Narayana & Ram 1983; Khan 1985) is almost five times the average rate observed in the United States. The estimated rate of storage loss in the conterminous 48 states in the United States is 0.22 percent per year (Crowder 1987). The rate of reservoir capacity lost to sedimentation is low in Britain (0.1 percent) but very high in China (2.3 percent) by global standards (Department of the Environment 2001; Liu et al. 2002; Wan 2005). In fact, the rate of storage loss in China is the highest of any country in the world (Zhou 1993; Morris & Fan 1998). It is almost five times higher than in India and ten times higher than in the United States. As mentioned by the National Bureau of Statistics of China (2013), there are 588 large reservoirs and 3,271 medium reservoirs with a total water volume of 3,400.7 G m3  by the end of 2012 (Yuan et al. 2015). China’s Yellow River has the highest sediment concentration of all the world’s major rivers. The rate of storage loss in the Middle East is 1.5 percent. The storage loss expressed in percentage in other regions is Turkey 1.5, South Africa 0.34, Southeast Asia 0.30, and Japan 0.15 (White 2001; Liu et al. 2002). Because of reservoir sedimentation, countries must construct about 300–400 new dams annually just to maintain the current total storage. Storage loss occurs mainly due to different vegetation cover, and topographic and geological conditions of watershed areas (Liu et al. 2002). The lack of understanding of sediment delivery patterns of rivers in several regions has resulted in the failure of several reservoirs (Xiutao 1986; Bhargava et al. 1987) as well as in the loss of expected economic gains (Tejwani 1984; Sharma 2001). At present, the sedimentation problem is so severe that agencies did not construct some dams because studies projected that the reservoirs would fill up with sediment due to excessive sedimentation rates before recovery of construction costs (Issa 2015). Some reservoirs in the world have silted up so fast that they have become unusable. The Camaré reservoir in Venezuela is an example of the consequences of sedimentation; loss of all storage occurred in less than 15 years (Morris & Fan 1998). The Yasuoka reservoir in Japan, on the Tenryu River, has lost 85 percent of its storage capacity in less than 13 years of operation due to accumulated sediment (Garde & Ranga Raju 1985; CWC 2001; Kantoush & Sumi 2010). Another example of a dam with a reservoir that filled up early is the Kebec dam in Turkey which lost 60 percent of its reservoir volume over 30 years (Simons & Şentürk 1992). In Iran, the Sefidroud dam faced a similar sedimentation dilemma (Othman et al. 2013). Huffaker et al. (2010), for example, stated that Cir-lurtsk reservoir on the Sulak River in Russia was 95 percent sedimented in 7 years; the Gumati reservoir on the Vakhs River in Georgia was 90 percent sedimented in 11 years; and the Zemo Afchar reservoir located at the confluence of the Kura River and Aragi River in Russia lost 44 percent of its initial storage capacity in the first 2 years of operation, 32 percent in the next 8 years, and 3.5 percent up to 1967. The Warsak dam, located on the Kabul River, Pakistan, lost as much as 18 percent of its storage capacity

4

Reservoir Sedimentation

in the first year of operation (Morris & Fan 1998; Jain & Singh 2003). In China, the Sanmenxia dam, built on the Yellow River in 1957–1960, stored a volume of 1.8 billion metric tons of sediment in the first 18 months of dam operation. The sediment deposition in the river up to about 260 km upstream from the dam is due to the back-water influence (Wu et al. 2007). In the state of Kansas in the United States, the reservoir of the dam built on the Salmon River filled totally within 1 year of its construction. The Matilija dam built in 1948 on the Ventura River in the state of California in the United States had a reservoir storage capacity of 1.6 M m3. The reservoir almost filled up with sediment in 1998 (Rogers & Kondolf 2007). The delta of the Mississippi River has lost over 4,800 km2 largely due to reduced sediment supply trapped upstream (Kondolf et al. 2014). The sediment transported by a flood caused a complete interment of the outlet structures of the Guayabal irrigation dam in southern Puerto Rico (Jain & Singh 2003). Indian government statistics stated that eleven of the country’s reservoirs with capacity greater than 1 km3 were filling up with sediment faster than the assumed rates (Nallanathel & Santhanam 2014). According to a survey during the year 2012 across 122 reservoirs in India, 0.44 percent of reservoir storage filled up with sediment every year. In the case of the Srisailam reservoir in Andhra Pradesh, commissioned in 1976, the percentage loss of capacity up to the last survey in 2011 is about 30 percent in a span of 35 years. Similarly, the capacity of Nagarjuna Sagar has decreased to about 24 percent in a span of 42 years (1967–2009). The project Nizamsagar in the Telangana region lost about 60.47 percent of its capacity within 62 years of its existence (CWC 2012, 2015; Rao et al. 2014). About 40,000 minor tanks in Karnataka lost more than 50 percent of their capacity. It is observed that, based on the sedimentation rate of 243 reservoirs, the calculated average annual percentage in gross storage loss due to siltation is 0.60 percent. The average annual percentage loss in dead and live storage is 0.494 percent and 0.04 percent, respectively, based on the sedimentation rate of 86 reservoirs (CWC 2015a). Before the industrial revolution, human beings lived and ancient civilizations developed and matured along the banks of rivers, especially in tropical countries. In the Indian sub-continent, the oldest known agricultural settlement, dating back to about 7000  BC, grew in Mehrgarh on the Bolan River at the junction of the Baluchistan plateau and the Indus plain. The Mehrgarh settlement preceded the Indus valley civilization or Harappan civilization which flourished in the Indian plains around 3000  BC (Mishra 1995). From that very ancient period, irrigation had a very long tradition in India. Indian scriptures are rich in examples of water measurement efforts and rational water harvesting measures. That tradition continues today. Since India’s independence from Great Britain in 1947, the top priority in India’s development planning programs is harnessing of river water resources through construction of large dam-based reservoirs known as Temples of Modern India (Bhattacharyya 1998, 2000, 2011). Developing countries have felt the need to apply scientific knowledge for economic and social benefit since the early 1940s (Bhattacharyya & Wiley 2014). In recent decades, worldwide dam management issues have increasingly captured the attention of the scientific community for ways to implement different sediment management strategies to tackle the future global water deficit (Morris & Fan 1998; CWC 2001, 2015; Jain & Singh 2003; ICOLD 2009; Graf et al. 2010; Luo et al. 2011; Annandale 2013; 2014; Kondolf et al. 2014; Rao et al. 2014; Annandale et al. 2016).

5

Introduction

1.2 GLOBAL WATER RESOURCES Availability of freshwater is a fundamental human right as declared by the United Nations (UN). However, a global concern exists about the future availability of freshwater due to increasing global population, which will grow to 9.8  billion by 2050 according to the new UN survey, with increasing future demands on freshwater (Vörösmarty et al. 2010; Annandale 2013). In many parts of the world, there is a growing scarcity of freshwater due to the unstoppable rise in demand for water to grow food, supply industries, and sustain urban and rural populations (Hoekstra et al. 2012). Shiklomanov (1987) depicted the dynamics of freshwater use by continents and for the world. The analysis of water use values obtained demonstrates that they are determined to a large extent by not only socio-economic conditions but also by climatic factors. The total amount of freshwaters on the Earth concentrate in aquifers, lakes, reservoirs, and river systems where they are most easily accessible for human health, food, industrial production, economic needs, and environmental ecosystems. Earth’s hydrosphere contains about 1,386 M km3 of water. The ocean contains 97.47 percent of all water on Earth which is saline and cannot directly fulfill freshwater supply needs (Table 1.1). The remaining 2.53 percent is freshwater and is either surface (77.78 percent) or subsurface (22.22 percent) water (Korzun 1974; Shiklomanov 1993; Shiklomanov & Rodda 2003) as detailed in Figure 1.2 (Christopherson & Birkeland, 2015). The two most abundantly available freshwater sources are groundwater and river water. TABLE 1.1 Water Reserves on the Earth Percentage of Global Reserves Volume 10 km 1,338,000 23,400 10,530 16.5 24,064 21,600 2,340 83.5 40.6 300 176.4 91 85.4 11.47 2.12 1.12 12.9 1,385,984 35,029 3

World ocean Groundwater Freshwater Soil moisture Glaciers and permanent snow cover Antarctic Greenland Arctic islands Mountainous regions Ground ice/permafrost Water reserves in lakes Fresh Saline Swamp water River flows Biological water Atmospheric water Total water reserves Total freshwater reserves Source: Shiklomanov, 1993.

3

Of Total Water 96.5 1.7 0.76 0.001 1.74 1.56 0.17 0.006 0.003 0.022 0.013 0.007 0.006 0.0008 0.0002 0.0001 0.001 100 2.53

Of Freshwater

30.1 0.05 68.7 61.7 6.68 0.24 0.12 0.86 0.26 0.03 0.006 0.003 0.04 100

FIGURE 1.2

Fresh 2.53%

Subsurface

Soil moisture Groundwater 0.18% 11.02%

Surface, 77.78%

Freshwater 2.78% of all

Deep groundwater 11.02%

Rivers and streams 0.003%

Atmosphere, 0.030%

Saline lakes, 0.280%

Freshwater lakes, 0.330%

Surface water percentage Ice and glaciers 99.357%

Distribution of Earth’s Freshwater Resources. (Source: After Christopherson and Birkeland, 2015.)

Ocean 97.47% 1.338 billion km3 (317 million ml3)

All water 100%

6 Reservoir Sedimentation

7

Introduction

Only freshwater flowing through the solar-powered hydrological cycle is a renewable resource (Postel et al. 1996). The waters of the hydrosphere are in constant, usually cyclic, motion through the hydrosphere, atmosphere, lithosphere, and biosphere under the effect of solar radiation, the energy released from the Earth’s interior and gravitational forces. Due to geological processes of outgassing, the Earth’s mantle releases about 1 km3 of water a year through degasification and this rises steadily to the Earth’s surface. Because of convection in the mantle, part of this gas or gaseous matter can emerge through breaks in ocean rift zones related to oceanic ridges. The global process of water exchange provides some constancy in the distribution of waters between the land, the oceans, and the atmosphere (Monin 1977; Shiklomanov & Rodda 2003; Annandale 2013; Christopherson & Birkeland 2015). Though the hydrological cycle connects water in the hydrosphere, the rates of movement and residence times are very different for water in its different states (Table 1.2). Estimates indicate that the period to complete recharge of oceanic waters takes about 2,500  years for permafrost, for ice about 10,000  years, and for deep groundwater and mountainous glaciers about 1,500 years. The replenishment rates for lakes are about 17 years but for rivers only about 16 days. Although river water is renewed on average over a period of 16 days, groundwaters are renewed very slowly, possibly over a period of a thousand years (Shiklomanov & Rodda 2003). Gleeson et al. (2012) calculated the global groundwater footprints of aquifers, which are important to agriculture and are considerably larger than their geographical areas (Figure 1.3). The estimate of the size of the global groundwater footprint is currently about 3.5 times the actual area of aquifers. Although, 80 percent of aquifers are not overdrawn, about 1.7 billion people are living in areas where groundwater resources as well as groundwater-dependent ecosystems are under threat. Figure 1.3 shows the areas of six aquifers (Western Mexico, High Plains, North Arabian, Persian, Upper Ganges, and North China Plain) at the same scale as TABLE 1.2 Periods of Renewal of Water Resources on the Earth Water of Hydrosphere World ocean Groundwater Polar ice Mountain glaciers Ground ice of the permafrost zone Lakes Bogs Soil moisture Rivers/channel networks Atmospheric moisture Biological water Source: Shiklomanov & Rodda 2003; Annandale 2013.

Period of Renewal 2,500 years 1,400 years 9,700 years 1,600 years 10,000 years 17 years 5 years 1 year 16 days 8 days Several hours

FIGURE 1.3 Major Groundwater Sources and Groundwater Footprints of Some Major Aquifers. (Source: Gleeson et al., 2012.)

8 Reservoir Sedimentation

9

Introduction

TABLE 1.3 Groundwater Footprints of Major Aquifers Aquifer Name Upper Ganges North Arabian South Arabian Persian South Caspian Western Mexico High Plains Lower Indus Nile Delta Danube Basin Central Mexico North China Plain Northern China North Africa Central Valley

Country

Groundwater Footprint

India, Pakistan Saudi Arabia Saudi Arabia Iran Iran Mexico USA India, Pakistan Egypt Hungary, Austria, Romania Mexico China China Algeria, Tunisia, Libya USA

54.2 48.3 38.5 19.7 98.3 26.6 9.0 18.4 31.7 7.4 9.1 7.9 4.5 2.6 6.4

Source: Gleeson et al., 2012.

the global map. The surrounding grey areas designate the groundwater footprint proportionally at the same scale. The South Caspian, Upper Ganges, and Western Mexico have groundwater footprints of 98, 54, and 27, respectively, representing that 98, 54, and 27 times more water is abstracted from those aquifers (Table 1.3). The aquifers presented with red colour are those having groundwater footprints greater than 20 and aquifers with blue colour having groundwater footprints of less than 1. The ratio GF/AA designates the widespread stress of groundwater resources and/or groundwater dependent ecosystems (Gleeson et al. 2012). The rate of groundwater reduction has increased significantly since about 1950, with maximum rates occurring during the most recent period of 2000–2008 (Konikow 2011), indicating a serious global problem threatening sustainability of water supplies (Schwartz & Ibaraki 2011). The distribution of the Earth’s water resources and river runoff are enormously uneven and categorized by multiple-year droughts. The uneven distribution is often the major determining factor for water scarcity (Postel et al. 1996). While the largest volume of water resources is in Asia and South America (13,500 and 12,000 km3 per yr, respectively), the smallest is typically found in Europe and Australia with Oceania (2,900 and 2,400  km3 yr –1). About 60 percent to 70 percent of runoff is formed during flood periods and therefore values for renewable water resources differ markedly during a year. Studies show that runoff takes place during April to July for the major part of Europe (46 percent), between June and September for Asia (54 percent), from September to December for Africa (44 percent), during April to July for South America (45 percent), and during January and April for Australia/Oceania

10

Reservoir Sedimentation

(40 percent). The utmost renewable water resources concentrate mainly in six principal countries—India, Brazil, United States of America, Canada, Russia, and China (Shiklomanov 1998; Shiklomanov & Rodda 2003). The rapid growth of population, the development of industrial production, and the rise of agriculture have resulted in the increased use of water (Shiklomanov 1997). About 80 percent of this water is used for agriculture, primarily for irrigation, and this causes more evaporation that intensifies the hydrological cycle (Babkin 2003). Global water use dynamics through the twentieth century to 2025, as has been depicted (Shiklomanov 1997; 1998), show that water abstractions in 1995 were 3,750 km3 yr –1, while consumption was 2,270 km3 yr –1. In the future, global water abstractions will grow by about 10 percent to 12 percent for each period of 10 years reaching 5,200 km3 yr –1 in 2025, a 1.38-fold increase. The total water withdrawal by 2025 is expected to be within the range of 10 percent to 12 percent of the above average value, that is, 4,600–5,800 km3 yr –1, if we count on uncertainties in developing economy, population growth, and climate change scenarios. At present about 70 percent of global water consumption occurs in Asia, the location of the major irrigated lands of the world. During the next few decades, studies predict that the most intensive development in water withdrawal will occur in Africa and South America (by 1.5–1.6 times) and the smallest in Europe and North America (1.2 times). The role of agriculture, however, will slightly decrease due to more intensive growth in industry and public services in the coming decades (Shiklomanov 1998). The water footprint, an indicator of direct and indirect appropriation of freshwater resources, includes both consumptive water use (the green and blue water footprint) and the water required to assimilate pollution (the grey water footprint). At the river basin level, studies computed large water footprints for the Mississippi, Ganges, Yangtze, Indus, and Parana river basins. These five river basins together account for 23 percent of the global water footprint related to crop production. Studies computed the largest green water footprint for the Mississippi River basin (424 G m3 yr –1). The largest blue water footprints were in the basins of the Indus (117 G m3 yr –1) and Ganges (108 G m3 yr –1) (Mekonnen & Hoekstra 2011). These two river basins together account for 25 percent of the global blue water footprint. Both basins are under severe water stress (Alcamo et al. 2007). Hoekstra and Mekonnen (2011) studied 223 river basins during 1996–2005 and mentioned that the blue water scarcity level exceeded 100 percent during at least one month of the year, which signifies that environmental flow requirements were violated during at least one month of the year. Annandale (2013, p. 20) mentioned that an economist, Herman Daly, while participating in the development of sustainable development policy guidelines for the World Bank, recommended that sustainable development could be achieved when: “(a) Renewable resources are used at a rate that is smaller than their rate of regeneration, (b) Exhaustible resources are used at a rate that is smaller than the rate of development of renewable substitutes, and (c), Pollution does not exceed the rate by which the environment can assimilate it.” The current human needs reserve in South Africa is set at 25 liters/capita/day, and many parts of the world do not have basic human needs reserve (Figure 1.4) emphasizing the importance of sustainable water resource development (Mekonnen & Hoekstra 2011;

11

Introduction Basic human needs reserve 25 liter/capita/day

80 70

71

Frequency (No. of countries)

60 50 43 40 30

28

20

16 9

10

3 0

10

20

30

40

50

60

1 70

3 80

Per capita consumption (liter/capita/day)

FIGURE 1.4 Histogram of Domestic Water Consumption in liter/capita/day. (Source: Mekonnen & Hoekstra, 2011; Annandale, 2013.)

Annandale 2013). The global depletion of groundwater is so great in most areas that it cannot recompense for declining water supplies caused by reservoir sedimentation (Morris 2016). By using three million Landsat satellite photos, scientists compiled a highresolution map of the Earth which offers an unprecedented glimpse into how our planet’s surface water has altered over the past three decades. Between 1984 and 2015, permanent surface water has disappeared from an area of almost 90,000 km2, though new permanent bodies of surface water, covering 184,000 km2, have appeared elsewhere. Much of the increase is due to reservoir filling, although scientists are also concerned about climate change as a possible factor (Pekel et al. 2016). Hence, the importance of reservoirs to today’s society will increase over time as population, economic activity, and irrigation demand grow and the need to adapt to climate change becomes more urgent (ICOLD 2010, Annandale et al. 2016). Therefore, river water has the utmost potential for sustainable development as a freshwater reserve source and policy emphasis should be on the development of rivers through creating and maintaining large reservoirs, known as carry-over-storage to counter the continual unsustainable use of groundwater resources (Annandale 2013). These reservoirs can convert uneven stream flows into reliable supplies of freshwater to mitigate demands for agricultural productivity and industrial use; for flood management; to maximize hydropower production; and to meet basic human needs (Plate 1.1).

12

Reservoir Sedimentation

PLATE 1.1 Grand Coulee Dam, constructed between 1933 and 1942, is a concrete gravity dam on the Columbia River in the state of Washington in the United States. Power production facilities at Grand Coulee Dam are among the largest in the world. Average yearly power production is 21 billion kWh with power distributed to the states of Washington, Oregon, Idaho, Montana, California, Wyoming, Colorado, New Mexico, Nevada, Utah, and Arizona. (Source of Photographs: U.S. Bureau of Reclamation, Washington, DC.)

1.3 DEVELOPMENT OF RIVER BASIN ORGANIZATIONS The decolonized Latin American, Asian, and African countries now control almost all major rivers. In India, as elsewhere, River Basin Organizations (RBOs) first arose as a mechanism for the integrated planning of large water development projects aimed at meeting growing requirements for power, irrigation, and industry. At the same time, governments and RBOs promised technological relief from flood hazards which had massive and disastrous impacts on riparian communities on a regular basis (Bhattacharyya 2011; Bhattacharyya & Wiley 2014). Offering the twin benefits of increased productivity and reduced environmental hazard, these countries subsequently accomplished the unified development of many river basins (White 1977; Saha 1981; Saha & Barrow 1981; Bhattacharyya & Wiley 2014). In newly constituted India, one of the first such RBOs was the Damodar Valley Corporation (DVC) created in 1948 and modeled on the Tennessee Valley Authority (TVA) of the United States. Proper utilization of river water resources and planning of future control projects on a sound basis are now two of the major issues in the water resources sector in India (Bhattacharyya 2011; Bhattacharyya & Wiley 2014).

1.4 DEVELOPMENT OF WATER RESOURCES THROUGH CREATING AND MAINTAINING DAMS/RESERVOIRS All development plans worldwide have given high priority to water resources projects involving the construction of dams and reservoirs for the development of renewable

Introduction

13

water resources as well as for flood control, irrigation, hydropower, domestic and industrial water supply, navigation, and so on. Mr. Pandya, Chairman of Central Water Commission (CWC), in his foreword to Compendium on Silting of Reservoirs in India (CWC 2015a), mentioned that in India the total live storage capacity of completed large and medium dams, as of March 2013, was 253 billion m3, that is, 37 percent of the projected utilizable surface water resources (690 billion m3). As the above mentioned storage is subject to silting, sedimentation of reservoirs is a matter of vital concern to all water resources development projects. Silting takes place not only in the dead storage but also in the live storage of reservoirs and reduces their envisioned benefits (CWC 2001, 2015a). This problem of sedimentation, which is affecting the design life and expected benefits of the dams and reservoirs, is universal and will continue to be a major concern globally in the coming decades and calls for careful consideration. Therefore, a review of reservoir sedimentation in India and elsewhere is timely.

1.5

GEOGRAPHICAL SCENARIO OF INDIA

India lies between 8°4′ to 37°6′ north latitude and 68°7′ to 97°25′ east longitude, encompassing 3.29 M km2 of area, half of which lies above the Tropic of Cancer and the remaining area in the tropics. The southern limit is close to the equator with a latitude of 8°4′ N. India’s landscape includes great mountains, extensive alluvial plains, riverine wetlands, plateaus, deserts, coastal plains, and deltas. The major physiographic divisions of the country are the Himalayas, the Indo-Gangetic plains, the Vindhyas, the Satpuras, the Western Ghats (Hills), the Eastern Ghats, the Coastal plains, the deltas, and the riverine wetlands (Figure 1.5). The term ghats refers to the terraced appearance of the mountains and the steps of terraces indicate successive lava flows. To the south of the Great Plains of northern India lies the Great Plateau of Peninsular India, divided into three parts: the Deccan Plateau, the Malwa Plateau, and the Chota Nagpur Plateau (GoI 2009; ICAR 2010). The Malwa Plateau, bounded by the Aravalli hills in the northwest and the Vindhyas, forms the northern half of this peninsula. The Chota Nagpur region forms the northern part of this plateau. The valley of the Narmada River forms the southern boundary of this plateau. The Deccan plateau extends from the Satpura hills in the north to the Kanyakumari, the southernmost point in India. It is bounded by the Vindhyas and the Western and Eastern Ghats. Towards the west of the Deccan plateau lie the Western Ghats. The Western Ghats comprise the Sahyadris, the Nilgiri, the Annamalai, and the Cardamom Hills. On the eastern side, the Deccan Plateau merges into the discontinuous low hills, known as the Mahendra Giri Hills, which encompass the Eastern Ghats. The Western Ghats landscape is composed of steep sided valleys, narrow gorges and waterfalls. Rivers and streams deeply dissect the steep seaward faces of the Ghats with many canyon-like valleys. Coastal India borders the Arabian Sea in the west and the Bay of Bengal in the east. Towards the western half of India lies a vast stretch of land divided by the Aravalli Mountains into two separate units. The area west of the Aravalli comprises the Thar desert, rock hills, and waterless valleys. The state of Gujarat lies east of this range. There are two major groups of islands in India classified as union territories: the Andaman and Nicobar Islands and the Lakshadweep Islands (GoI 2009; ICAR 2010).

14

Reservoir Sedimentation

FIGURE 1.5 Physiographic Regions: India. (Source: National Atlas and Thematic Mapping Organisation (NATMO), Kolkata, India.)

1.5.1

PhysiograPhic regions

The Indian subcontinent physiography ranges from the Himalayas proper in the north to the deep oceans to its south, the arid sunny Thar desert in the west to the mangroves of Sundarbans in the East, and the cold Ladakh desert up in the hills. India has seven well-defined physiographic regions (Figure 1.5): 1. The Northern Mountains, comprising the mighty Himalayan ranges 2. The Great Plains, traversed by the Indus and the Ganga-BrahmaputraMeghna River systems

Introduction

15

3. The Central Highlands comprising the Aravalli, the Vindhyas and the Satpura ranges 4. The Peninsular plateaus comprising the Western Ghats, the Eastern Ghats, the Deccan Plateau, the Malwa Plateau, and the Chota Nagpur Plateau 5. The East Coast, a belt of land about 100–130 km wide, bordering the Bay of Bengal and lying to the east of the Eastern Ghats 6. The West Coast comprising the Konkan and Malabar Coasts, a narrow strip of land about 10–25 km wide bordering the Arabian Sea 7. The Islands comprising coral islands of Lakshadweep in the Arabian Sea and the Andaman and Nicobar Islands in the Bay of Bengal

1.5.2

geology

India has a diverse geology, just as it has a diverse geography and people, which began with the geological evolution of the rest of the Earth 457 million years ago (Mya). The India–Asia collision is perhaps the most recent and continuing tectonic uplift to have occurred in the past 100 million years. It is responsible for the uplift of the Himalayas and associated mountain ranges and the Tibetan Plateau and is arguably responsible for geological, geochemical, and climatological consequences of global extent (Rowley 1996). Peninsular India to the south embodies one of the oldest and least disturbed large land masses which comprise Archaean rocks which are the oldest in the world. Between the Peninsula and the Himalayas lie the Indo-Gangetic plains. During the Triassic period of about 251–199.6 Mya, the Indian subcontinent was part of a vast supercontinent known as Pangaea, meaning all lands in Greek. India was then situated well south of the Equator. The breakup of the supercontinent Pangaea has a prominent role to play in the theory of continental drift. Pangaea began to break up about 225–200 Mya, eventually fragmenting into the continents as we know them today. The 6,000-km-plus journey of the Indian landmass (Indian Plate) before its collision with Asia (Eurasian Plate) happened about 40 to 50 Mya. The collision triggered the Eurasian Plate to crumple up and supersede the Indian Plate. Afterwards, the slow continuous convergence of the two plates over millions of years pushed up the Himalayas and the Tibetan Plateau to their present heights. Most of this development happened during the past 10 million years (Chumakov & Zharkov 2003). This tectonic movement by the Indian Plate caused it to pass over a geologic hotspot known as Réunion, an island found in the Indian Ocean east of Madagascar, and resulted in a massive flood basalt event on the Deccan Traps at the end of the Cretaceous period some 60–68 Mya (Iwata et al. 1997; Sheth 2005a; Sheth 2005b). That is why the rocks found in this region are generally igneous in character. It is also thought that the Réunion hotspot caused the separation of Madagascar and India. The peninsula has extensive areas of ancient sedimentary rocks superimposed on the Archaean base. Its rocks were always exposed and have never been extensively covered by the sea since their creation during the pre-Cambrian period over 300 Mya, though they do include some sedimentary strata deposited by rivers and under glacial conditions. The oldest of these is the Vindhyan series, still dating from the pre-Cambrian period. The most important post-Cambrian system in the peninsula is the Gondwana series of sedimentaries. The Gondwana and Vindhyan series include parts of Madhya Pradesh, Chhattisgarh, Odisha, Bihar, Jharkhand, West

16

Reservoir Sedimentation

Bengal, Andhra Pradesh, Maharashtra, Jammu and Kashmir, Punjab, Himachal Pradesh, Rajasthan, and Uttarakhand. The Gondwana Supergroup forms a unique sequence of fluviatile rocks deposited in Permo-Carboniferous times. The Damodar and Sone River valleys and the Rajmahal hills in eastern India are a depository of Gondwana rocks. As a result, different regions in India comprise rocks of all types belonging to different geologic time periods. India’s geographical land area can be classified into the Deccan trap, Gondwana, and Vindhyan areas (Robinson 1989; Bhagwat 2009, Figure 1.6).

FIGURE 1.6 Geology of India. (Source: National Atlas and Thematic Mapping Organisation (NATMO) and Geological Survey of India (GSI).)

Introduction

1.5.3

17

climate

The Himalayas form a barrier to frigid Central Asian air, preventing it from reaching India. Hence, India’s climate is significantly warmer and more tropical in character. In general, since the greater part of India lies within the tropics, it has a variable tropical monsoon climate and is subject to cyclical drought. According to the Köppen system of climate classification, the climate of India resolves into four major climatic subtypes: (1) desert in the west, (2) alpine tundra and glaciers in the north, (3) humid tropical regions accompanying rain forests in the southwest, and (4) Indian Ocean island territories that border the Indian subcontinent. The large size of the country, the position of the mountain ranges, and route of the rain-bearing winds are the main determining factors for the climatic variations in the different parts of India. Besides that, the apparent seasonal rhythm of the monsoons and the alternating seasons are the chief characteristics of India’s climate (Ravindranath et al. 2011). India Meteorological Department (IMD) categorizes the four official seasons as: 1. Winter (December to early April): The year’s coldest months are December and January when temperatures average around 10°C–15°C (50°F–59°F) in the northwest. Temperatures rise as one proceeds towards the equator, peaking around 20°C–25°C (68°F–77°F) in the mainland of India’s southeast. The northeast monsoon covers all of India during this season. Tamil Nadu receives most of its annual precipitation in the northeast monsoon season. The mean January day temperatures in Asansol and in Chennai and Calicut are about 19°C and 24°C–25°C, respectively, while in the northern plains it is about 10°C–15°C. 2. Summer (pre-monsoon: April to June): In the western and southern regions, the hottest month is April; for northern regions, May is the hottest month. Temperatures average around 32°C–40°C (90°F–104°F) in most of the interior. From mid-March to May, the sun moves over the Equator towards the Tropic of Cancer. By June 21, it is directly over the Tropic of Cancer. In March, the highest day temperatures of about 39°C and 38°C occur in Asansol, West Bengal, and in the Deccan Plateau, respectively. Therefore, the temperature profile is as follows: a. Peninsular India or places south of Satpuras experience temperatures between 26°C and 32°C. b. Central India, comprising Delhi and Madhya Pradesh, experiences temperatures between 40°C and 45°C. c. North-West India, comprising mainly Rajasthan, has very high temperatures (45°C) due also to features such as sandy soil, direct insulation, and lack of cloud cover. 3. Monsoon (rainy: June to September): A monsoon is a seasonal shift in the wind direction. In a true monsoon climate and seasonal wind shifts typically cause a drastic change in the general precipitation and temperature patterns. From mid-June to the end of October, monsoon rains cause low clouds, swollen rivers, and flooded villages. This moisture is the result of cooler, moisture-laden air moving from the ocean over the land.

18

Reservoir Sedimentation

Nearly 2 months of scorching temperatures cooled only with the commencement of summer rains brought by the southern westerlies precede the rainy season that typically begins in June. The rainy months, from June to October, account for more than 80 percent of the total annual rainfall and falls in most of the areas situated above 16° N latitude, except the Ladakh plateau, Kashmir Himalayas, and southern tips of the Deccan peninsula. The monsoon hydrograph is leptokurtic in nature. Peak discharge is generally in the months of July–September. Discharge is low between January and May and again between November and December (Bhattacharyya 2011). 4. Post-monsoon (October to December): In northwestern India, October and November are usually cloudless. In December, the sun shines directly over the Tropic of Capricorn. The landmass of Asia cools down very rapidly. There is a high pressure over the continent. The Indian Ocean, being warmer, has a relatively low pressure. The vagaries of South Asian summer monsoon rainfall impact the lives of more than one billion people. There is widespread scientific consensus that South Asia is likely to see climatic events that will become more unpredictable with changes in frequency and increased severity (Andrew et al. 2012). Climate change potentially introduces a new and troubling feature into the functional relationship between river control practices and flood hazard (Bhattacharyya & Wiley 2014). The current patterns of destructive floods, increasing intensity of cyclones, sea level rise, frequent droughts, and increasing temperatures are all attributable to global warming. With continuing rise in CO2 and global warming, the South Asian region can expect generally more rainfall due to the expected increase in atmospheric moisture, as well as more variability in rainfall pattern (CSWCRTI 2011; STAP 2012; Turner & Annamalai 2012). 1.5.3.1 Precipitation The alignment of hills and mountains has a profound influence on the prevailing winds and thereby the distribution of rainfall in the country (Figure 1.7). India receives, on average, about 4,000  km 3  of annual precipitation (including snowfall) every year which is one of the highest in the world for a country of comparable size. There are temporal and spatial variations in the distribution of rainfall and hence in the availability of water in time and space within the country (India-WRIS). For purposes of rainfall assessment, the India Meteorological Department divides the country into 35 hydro-meteorological subdivisions (cited in Tyagi, 2003). Annual normal rainfall varies considerably by season among different meteorological subdivisions. The period of July–September is the principal rainy season for almost the entire country, when 70 percent to 90 percent of the total rainfall falls in most of the areas located above 16° N latitude, except the Ladakh plateau, Kashmir Himalayas, and southern tips of the Deccan peninsula. Some rains fall as winter rains during October– February. Annual rainfall fluctuates from 100 mm in the Thar desert of Rajasthan to over 11,000 mm in Cherrapunji-Mawsynram of Meghalaya (ICAR 2010).

Introduction

19

FIGURE 1.7 Distribution of Rainfall. (Source: National Atlas and Thematic Mapping Organisation (NATMO), Kolkata, India.)

More than 1 M km2 of the country’s geographical area receives inadequate rainfall. This area includes the western desert, the semi-arid region, the regions of north India, and the rain shadow of the Western Ghats. The Western Ghats receive both southwest and northeast monsoon rains averaging about 500  cm annually. During the southwest monsoon period, rainfall of high order falls on the windward side of the Western Ghats and decreases rapidly towards the leeward side. The IndoGangetic plain and the Himalayas also receive rainfall surpassing the national average.

20

Reservoir Sedimentation

The  Damodar valley, especially the Lower Damodar valley, a subsystem of the Ganga, is generally a wet area with high incidence of rainfall and despite year to year fluctuations, it averages at well above 172 cm yr –1 (DVC 1995; Bhattacharyya 2011). Large rivers in peninsular India, such as the Godavari, the Krishna, the Pennar, and the Cauvery, pass through extensive tracts of low rainfall areas carrying less water than the rivers passing through high rainfall areas of the northeast and the west coast. In the northeast, the Khasi and Jaintia hills receive rainfall of 1,000 cm annually and river valleys, such as that of the Brahmaputra, get precipitation on the order of 200 cm. Rainfall up to 1,142 cm falls in Cherrapunji and Mawsynram and is one of the highest levels of rainfall in the world. The spatial and seasonal variation of rainfall is well noted here. The Western Ghats, Assam, parts of sub-Himalayan West Bengal, and some higher elevations of Himalayas up to Punjab have more than 100 rainy days a year, while in the extreme desert land in Rajasthan the number of rainy days is less than 10. Snowfall occurs only in the high Himalayan region (Rao 1979; Sugunan 1995). P.R. Pisharoty, one of India’s prominent meteorologists, indicates that the nature of Indian rainfall is totally different from that of other middle latitude countries of Europe. India receives some 400 million hectare meters of rain annually over a geographical area of 329 million hectares (mha). This rainfall, if evenly spread, would uniformly inundate the entire land surface to a depth of about 1.28 m. But rainfall is not evenly distributed and has a large spatial and temporal variation causing floods in some parts of the country and droughts at the same time in other parts (Agarwal & Narain 1997). India does not receive rainfall throughout the year. Rainfall occurs mainly in the monsoon months of June to September. Rainfall does not occur daily; most parts of the country get fewer than 50 days of rainfall a year. On the days when rainfall occurs, it does not fall over a period of 24 hours. Most of the country receives rains of just about 100 hours in a year (Agarwal & Narain 1997). According to Pisharoty, “a thumb-rule is that the number of hours of rain a place receives in a year is equal to the number of centimeters of rain it receives annually.” Delhi with an annual rainfall of 80 cm receives this in just 80 hours; Nagpur receives 100 hours of rain in a year, and Jodhpur receives rains for just 40 hours a year. Pisharoty stresses that half the annual rainfall precipitates in just one fifth of the total hours of rain in a year. Thus, if a town receives 80 cm of rain, half of it, that is 40 cm, falls in just 16 hours. In India, half of the total annual rainfall falls in about 20 hours. Pisharoty recalls that Ahmedabad, with 800 mm annual rainfall, once received 320 mm in 6 hours in a massive downpour. Parts of Rajasthan have in the past received twice their average rainfall in just 2 days. This type of rainfall naturally generates a large amount of runoff within short bursts of time, making it imperative to store this water if it is to be of use. Of the total rain that falls on the Indian subcontinent, only a small quantity percolates into the ground (Agarwal & Narain 1997). The southwest monsoon season, which is the principal rainy season, extends from June to September and receives about 90 percent of the annual rainfall. Thus, the surface inflow covers a brief period of 2 to 3 months. Typically, there are 10 to 15 rainy days in most parts of the country. Flood hydrographs of the Damodar River manifest these characteristics (Figure 1.8a–c).

21

Introduction 2500

1934 1946 1959 1965 1978 1984 1985 1995 2005 2007

Streamflow (m3/s)

2000 1500 1000 500 0

Jan

(a)

Feb Mar Apr May Jun Jul Months

Aug Sep Oct Nov Dec

Monthly Streamflow to Mean Annual Streamflow (percent)

120 POST-DAM (1959–2007)

80 March to May June to September Oct to Nov Dec to Feb

60 40 20

2007

2004

2001

1998

1995

1992

1989

1986

1983

1978

1974

1971

1967

1960

1957

1954

1950

1947

1944

1941

1938

1934

0

(b)

PRE-DAM (1934–1956)

100

Year

(c)

FIGURE 1.8 (a) Flood Hydrographs of Damodar River. (b) Discharge Characteristics of the Lower Damodar River at Rhondia in Pre-dam (1934–1956) and Post-dam (1959–2007) Periods (Percentage of Streamflow with Respect to Mean Annual Total Streamflow). (Source: Bhattacharyya, 2011.) (c) Flood Hydrographs of the Lower Damodar River at Different Sites During September–October 1978 Flood. (Source: Sen, 1993.)

22

Reservoir Sedimentation

FIGURE 1.9 Hazard Map of India. (Source: National Atlas and Thematic Mapping Organisation (NATMO), Kolkata, India.)

Deficient rainfall causes droughts in parts of India. Studies have recognized a total of 74 districts in 13 states of the country as drought-prone encompassing a drought-prone area of 51.1 M ha against 329 M ha of the country’s total geographical area (Figure 1.9). Gujarat, Rajasthan, Western Uttar Pradesh, parts of Tamil Nadu, Andhra Pradesh, and Karnataka face droughts every 3 years on the average. Scientists place much emphasis on the growth of irrigation facilities in those places through the creation of storage reservoirs (Tyagi 2003). Thus, extreme seasonality of rainfall distribution makes the reservoirs a sine qua non for agriculture and for control of floods and droughts in India.

Introduction

1.5.4

23

soils

Soil is a finite and non-renewable natural resource. It takes between 200 and 1,000 years for 2.5 cm of topsoil to build up under cropland conditions (Pimentel et al. 1995). The main soil types of India include alluvial, deep and medium black, red and yellow, laterite, saline and desert, and forest and hill (Figure 1.10). Since India is primarily an agricultural country, the success of agriculture depends upon the fertility of soils.

FIGURE 1.10 Main Soil Types. (Source: National Atlas and Thematic Mapping Organisation (NATMO), Kolkata, India.)

24

Reservoir Sedimentation

Alluvial soils or riverine soils cover about 40 percent of land area in India formed by the deposition of fine sediments and silt by the rivers along their banks. These soils are mostly in the Great Northern Plains, the coastal plains, and river deltas. The whole of the northern plains, from Punjab, Haryana, Uttar Pradesh (U.P.), and Bihar to West Bengal, are in this region. The river courses and the deltas form alluvial soil regime. In the Great Northern plains, floods result in the deposition of silt. This new alluvium is known as Khadar. The higher areas, where floods do not reach, have old alluvium and are known as Bangar. The southern coastal area starts from the eastern coast along a narrow belt passing through the flood plains, terraces, deltaic, and lagoon areas of the rivers, such as the Mahanadi, the Godavari, the Krishna, and the Cauvery. Narrow areas along the coast and lower portions of the Narmada, the Tapti, the Sabarmati, and the Mahi also have such types of soils. The alluvial soils are fertile, deep soils rich in potash but poor in nitrogen. These soils are responsible for making the northern plains the granary of India and enhance agricultural activities and crop productivity. The solidification of volcanic lava formed black soils thousands of years ago. These soils developed in the Deccan Lava Trap area on basalt rocks in semiarid conditions. Such soils are in eastern Gujarat, southwestern Madhya Pradesh (Narmada, parts of Vindhya and Satpura), almost the whole of Maharashtra, northern Karnataka, northwestern Tamil Nadu, and western Andhra Pradesh. These soils are rich in lime, iron, magnesia, and alumina, but lack phosphorus and nitrogen and are almost completely devoid of humus. This is also known as Black Cotton Soil or Regur Soil, a word derived from the Telugu word reguda. The Deccan Trap area has become famous for cotton cultivation because of these soils. In fact, this region is the cotton bowl of India. Red and yellow soils formed due to the decomposition of underlying igneous rocks under heavy rainfall. The reddish-yellow coloured soils usually developed on old crystalline and metamorphic rocks and where rainfall is low and there is less leaching than in laterite soils. These soils are in parts of Meghalaya, Nagaland, Manipur, Mizoram, the Chhotnagpur plateau, Telangana, Nilgiris, Tamil Nadu, Karnataka, Andhra Pradesh, and periphery areas of Deccan Plateau. Laterite soils are in high temperature areas that receive heavy rainfall with alternate wet and dry periods. Due to higher temperatures, the bacteria eat away humus and rainfall leaches silica and lime. As a result, the soils are shallow, acidic, and rich in aluminium and iron oxide and are less fertile. These soils are in Karnataka, Kerala, Tamil Nadu, and hilly regions of Assam, Rajmahal hills, and the Chhotanagpur plateau. Arid and desert soils are in most of the arid and semi-arid region of Rajasthan and adjoining areas of Punjab and Haryana. Desert soils are in arid regions that receive very little rainfall. These soils are usually shallow with sandy texture. They have low clay and salt content. The colour ranges from red to brown and light brown.

Introduction

25

Saline soils are in various climatic regimes, including dry, semi-dry, and swampy. These soils possess sodium, potassium, and magnesium salts. Salts reach these areas through defective drainage and dry climate. The southwest monsoons, which cross Rann of Kutch, bring with them salt particles that form a layer in the state of Gujarat. In the swampy areas and in the coastal tidal areas, salt saturates them. These soils are deficient in nitrogen and calcium. The western Gujarat area (Kutch) is known for this type of soil. In the Cauvery and Mahanadi deltas, the sea water makes the soil saline. In West Bengal, the Sundarbans are well known for such soils. In Punjab, Haryana, Uttar Pradesh and Bihar, saline soils are encompassing more and more agricultural areas. This is true for the southern Indian states as well. Peaty and organic soils are in the coastal areas of West Bengal, Orissa and Tamil Nadu, northern Bihar, and the Almora area of Uttarakhand. A large amount of dead organic matter accumulates in areas that have heavy rainfall and high humidity. As a result, these soils are saline, rich in organic matter (40 percent) but deficient in potash and phosphorus. These soils are alkaline, heavy, and black in colour. Forest and hill soils are in hilly areas covered with forests. The main characteristic of these soils is the accumulation of organic matter derived from forest cover. The soils are not uniform everywhere and there are variations in their distribution. The soils are loamy and have silt in the valley areas and are coarse grained with kankar, and so on, in high elevation areas (UNEP 2001; ICAR 2010).

1.5.5

river systems

A river basin is the basic spatial unit for planning and development of water resources. The network of rivers in India comprises 14  major river basins having a combined catchment area of about 25.3 105 km2 (Figure 1.11a). These are the Ganga-Brahmaputra-Meghna, the Indus, the Subarnarekha, the Godavari, the Krishna, the Cauvery, the Mahanadi, the Pennar, the Brahmani-Baitarni, the Sabarmati, the Mahi, the Narmada, and the Tapi. The major river basin is the Ganga-Brahmaputra-Meghna, which is the largest with a catchment area of about 11.0 105 km2 comprising more than 43 percent of the catchment area of all the major rivers in the country. In addition, there are 46 medium drainage basins varying in size from 2,000 to 20,000  km2  and minor drainage basins with catchment areas below 2,000 km2. Table 1.4 shows catchment areas and lengths and annual average discharges of major rivers. Table 1.5 gives the basin-wide distribution of surface water potential (CWC 1998; Rangachari et al. 2000). These river systems can be classified into four groups (CBIP 1991; WRIS-India): 1. Himalayan rivers: The main Himalayan River Systems are those of the Indus and Ganga-Brahmaputra-Meghna Rivers. 2. Deccan rivers: Some important river systems in the Deccan plateau of peninsular India are the Narmada and the Tapi, which flow westwards

26

Reservoir Sedimentation

(a) 100% 80% 60% 40% 20% 0% (b)

63

28 10

55

3.5 33.5

62

5 40

Area

Water Utilizable resources water resources

FIGURE 1.11 (a) River Systems. (Source: National Atlas and River Basin Organization (NATMO), Kolkata, India.) (b) Distributions of Water Resources in Different Regions of India. (The Ganga-Brahmaputra-Meghna, West Flowing Rivers below Tapi and Other Basins) (Source: Tyagi, 2003.)

27

Introduction

TABLE 1.4 Length, Basin Area, and Annual Average Discharge in the River Basins of India Name of River Brahmaputra Ganga Indusa Sabarmati Mahi Narmada Tapi Mahanadi Brahmani Subarnarekha Godavari Krishna Pennar Cauvery a

Length (km)

Basin Area (km2)

Annual Average Discharge (M m3)b

720 2,525 760 300 533 1,312 724 857 800 395 1,465 1,400 597 800

258,008 760,407 320,184 21,445 33,866 99,171 62,845 138,889 39,033 19,296 312,812 257,923 55,213 87,900

627,800 468,700 41,955 3,800 11,800 54,600 17,982 66,640 18,310 7,940 118,000 67,675 3,238 20,950

Basin area in India and discharge at the international boundary. Discharge at low tide at the point of entrance into the sea, excluding the cases of the Brahmaputra and the Indus. Source: Indian Government River Basin Atlas of India (1985). a

b

into the Arabian Sea, and east-flowing rivers, such as the Brahmani, the Mahanadi, the Godavari, the Krishna, the Pennar, and the Cauvery that flow to the Bay of Bengal. Because of the uplift of the Western Ghats, all the important rivers of Deccan Plateau, except the Narmada and the Tapi, flow eastward to the Bay of Bengal, although they have their origin on the crest of the Western Ghats situated only 50–80 km away from the Arabian Sea coast. 3. Coastal rivers: There are innumerable coastal rivers which are comparatively small. There are as many as 600 such rivers on the west coast and only a handful of such rivers drain into the sea near the deltas of the east coast. The west coast rivers are of great significance, as they constitute as much as 10 percent of the country’s water resources while draining only 3.5 percent of the land (Figure 1.11b). 4. Rivers of the inland drainage basin: A few rivers in Rajasthan do not drain into the sea. They drain into salt lakes or remain in sands with no outlet to the sea.

28

Reservoir Sedimentation

TABLE 1.5 Water Resources Potential in River Basins of India

Name of River Basin Indus (up to border) Ganga Brahmaputra, Barak, and others West Flowing Rivers From Tadri to Kanyakumari From Tapi to Tadri Narmada Tapi Of Kutch, Saurashtra including Luni Mahi Sabarmati Area in Inland Drainage in Rajasthan East Flowing Rivers Godavari Krishna Mahanadi Brahmani and Baitarni Subarnarekha From Mahanadi to Godavari and Krishna to Pennar Cauvery Pennar Between Pennar and Kanyakumari Minor River Basins Draining into Bangladesh and Myanmar Total Percentage in Billion Cubic Meters (BCM)

Average Annual Potential in the River (Percent)

Estimated Utilizable Flow Excluding Groundwater (Percent)

3.92 28.09 31.33

6.66 36.22 3.48

6.07 4.68 2.44 0.80 0.81 0.59 0.20 0.00 5.91 4.18 3.58 1.52 0.66 1.20 1.14 0.34 0.88 1.66 100.00 1,869.37

3.52 1.73 5.00 2.10 2.17 0.45 0.28 0.00 11.05 8.40 7.24 2.65 0.99 1.90 2.75 0.99 2.42 100.00 690.32

Source: CWC, 1998; Rangachari et al., 2000.

1.5.6

Distribution of Water resources

Annual precipitation, including snowmelt, received on the Indian land mass averages about 4,000 km3 and is the main source of water. The country also receives 390 km3 of flows from other countries. Projections for natural evaporation are about 2,316 km3 and the residual 1,869 km3. The estimated natural water resources of India are 2,074 km3 (4,000  +  390  −  2,316  =  2,074), manifesting itself as surface water and groundwater (Tyagi 2003). Based on per capita water availability, India ranks 42 out of 100 countries, not a privileged position. Out of this total water availability, only 1,123 km3 is exploitable (690 km3 from surface water resources and 433 km3 from groundwater resources). Water demand in the year 2000 was 634 km3 and it will likely be 1,093 km3 by the year 2025. Economy and population growth remain rapid, so there will be increasing demand for water and it will become increasingly limited in the coming decades (Tables 1.6 and 1.7).

29

Introduction

TABLE 1.6 Water Availability Facts at a Glance Area of the country as percent of world area Population as percent of world population Water as percent of world water Rank in per capita availability Rank in water quality Average annual rainfall Range of distribution Range rainy days Range PET Per capita water availability (2010)

2.4 percent 17.1 percent 4 percent 132 122 1,160 mm (world average 1110 mm) 150–11,690 mm 5–150 days, mostly during 15 days in 100 hours 1,500–3,500 mm 1,588 m3

Source: India-wris.nrsc.gov.

TABLE 1.7 India’s Water Resources SI No 1 2 3 4 5 6 7 8 9 10 11 12

Water Resource at a Glance

Quantity (km3)

Percentage

Annual precipitation (including snowfall) Precipitation during monsoon Evaporation + soil water Average annual potential flow in rivers Estimated utilizable water resources Surface water Replenishable groundwater Storage created of utilizable water Storage (under construction) of utilizable water Estimated water need in 2050 Estimated deficit Interlinking can give us

4,000 3,000 2,131 1,869 1,123 690 433 253.381 50.737 1,450 327 200

100 75 53.3 46.7 28.1 17.3 10.8 22.52 4.5 129 29 17.8

Source: INDIA-WRIS, 2011.

A country can be classified as water stressed when water accessibility is less than 1,700 m3 per capita per year, whereas it is categorized as water scarce if it is less than 1,000 m3 per capita per year. In India, the availability of surface water in 1991 and 2001 was, respectively, 2,309 and 1,902 m3. However, projections for per capita surface water availability is likely to decrease to 1,401 and 1,191 m3 by 2025 and 2050, respectively. The per capita water availability in the country was 1,588 m3 in 2010 compared to 5,200 m3 in 1951 (WRIS-India). The distribution of water resources in India is highly skewed due to the spatial and temporal variation in rainfall and, therefore, inaccessibility of water in time and space across the country. The Ganga-Brahmaputra-Meghna basin, covering

30

Reservoir Sedimentation

33.5 percent of the country’s area, contributes 62 percent of water resources, whereas, the west flowing rivers, with only 3.5 percent of the area, contribute as much as 10 percent of the water resources (Figure 1.11b). The variability in population density further accentuates the water shortage problem. The basinwide per capita water availability, which is around 1,859 m 3 yr –1 for India, varies between 13,393 m 3 yr –1 for the Brahmaputra-Barak basin to about 300 m 3 yr –1 for the Sabarmati basin (Tyagi 2003).

1.5.7

river systems anD associateD flooD Problems

The rivers in India are broadly divided into the following four groups to study the flood problem: The Brahmaputra region, the Ganga region, the North West region, and the Central India and Deccan region. The National Flood Commission (RBA) (1980) measured the total flood prone area as 40 M ha, including the unprotected flood area of 33.516 M ha and 6.484 M ha as protected area. A two-tier system of flood management, that is, State Level Mechanism and Central Government Mechanism, exists in India. India has implemented different measures categorized as engineering or structural measures and administrative or non-structural measures to reduce flood losses and defend the flood plains. Different aspects of the engineering or structural measures include reservoirs and embankment construction, channelization of rivers, channel improvement, drainage improvement, and diversion of flood waters. The administrative methods attempt to alleviate flood damages by emphasizing flood plain zoning and flood proofing (Ray 2013; WRIS: India).

1.5.8

bioDiversity

From the perspective of biodiversity, India is one of the 17 recognized megadiverse countries of the world, with only 2.4 percent share of the total land area of the world. From about 70 percent of the total geographical area surveyed, 45,500 plant species and 91,000 animal species, signifying about 7 percent of the world’s flora and 6.5 percent of the world’s fauna, have been identified (GoI 2009). It is estimated that at least 10 percent of the country’s recorded wild flora and fauna are on the endangered list, many on the verge of extinction. India has two biodiversity hot spots: the Eastern Himalayas and the Western Ghats. India, with varied terrain, topography, land use, and geographic and climatic factors, can be divided into ten recognizable biogeographic zones (Rodgers et al. 2000) which contain a variety of ecosystems, including mountains, plateaus, rivers, forests, deserts, wetlands, lakes, mangroves, coral reefs, coasts, and islands. The ten recognizable biogeographic zones (Figure 1.12) are the Trans-Himalayan Region, Himalayan Zone, Indian Desert Zone, Semi-Arid Region, Western Ghats, Deccan Plateau, Gangetic Plain, North-East Region, Coasts, and Andaman/Nicobar Islands. Wetlands are species-rich habitats and provide valuable ecosystem services as well as other benefits to people (Verhoeven & Setter 2010). The distribution of wetlands is in different biogeographical zones in India. During the past few decades, public appreciation of the ecological, social, and economic value of wetlands has increased considerably (Conservation Foundation 1988; Gopal & Sah 1995; Dahl 2000). Although wetland protection is officially a priority

31

Introduction Biogeographic classification

Biogeographic regions Coasts Deccan Peninsula Desert Gangetic plain Himalaya Islands North East Semi-Arid Trans-Himalaya Western Ghats

FIGURE 1.12 2007, MoEF.)

Biogeographical Classification. (Source: State of Environment Atlas of India,

for the 163 nations (as of January 2013), including India, that have approved the Ramsar Convention (2013), wetlands continue to be drained and reclaimed (Verhoeven & Setter 2010). Wetland conservation requires a holistic outlook that views each wetland in terms of its causal connectivity with other natural entities, human requisites, and its own attributes (USDA 2012). The Convention on Wetlands (Ramsar, Iran, 1971), an intergovernmental treaty, has its mission defined as “the conservation and wise use of all wetlands through local, regional, and national actions and international cooperation, as a contribution towards achieving sustainable development throughout the world.” India plays a significant role in conservation and wise use of wetlands. With 76.87 M ha of forest and tree cover, India ranks tenth in the list of most forested nations in the world and provides critical ecosystem goods and services (Kishwan et al. 2009). In India, forests cover about 23.6 percent of the total geographical area of the country (FSI 2005; Kishwan et al. 2009) compared to the ideal requisite of 33 percent (ICAR 2010). The panorama of Indian forests spans evergreen tropical rain forests in the Andaman and Nicobar Islands, the Western Ghats, and the Northeastern States, to dry alpine scrub high in the Himalayas to the north. Between the two limits, India has semi-evergreen rain forests, deciduous monsoon forests, thorn forests, and subtropical pine forests in the lower mountain zone and temperate mountain forests

32

Reservoir Sedimentation

(Lal 1989). With profound demographic changes, the land to human ratio and forest to human ratio has rapidly declined (GoI 2009). Over the past decades, India has directed national policies towards conservation and sustainable management of forests and has transformed India’s forests into a net sink of CO2 (Kishwan et al. 2009).

1.6

DAM/RESERVOIR SCENARIO

Indian scriptures are rich in examples of human efforts to implement effective water harvesting measures. The scriptures, such as the Vedas, are the oldest scriptures in the world and the Vedic period extends between 6500 BC to 800 BC (Chattopadhyay 1990). The scriptures mention the significance of water bodies, natural or artificial, for irrigation. The Rig-Veda uses a term Avata which implies a well. At the same time, there are references to Kulya, an artificial river or canal. In another passage there is a reference to a dried-up reservoir. The Yayur Veda also refers to canals and dams which were known as Kulya and Sarasi. Sarasi, in fact, represents an artificial reservoir or a natural lake. The Atharva Veda (III, 13) gives a clarification of the construction of canals from rivers. A canal is fed by a river or, in other words, a canal takes off from a river. To elucidate this idea, the Atharva Veda uses the metaphor of a canal as a calf and the feeding river as a cow (Sarava 1954). Ramayana, the first epic (before the fifth century BC), describes in detail how King Bhagiratha and his group of engineers diverted the course of the Ganga from the Himalayas towards the present Ganga delta. Bhagiratha probably tried to improve the agricultural condition of Lower Bengal by cutting artificial canals (Bhattacharyya 2011). In his report, Willcock (1930), an Egyptian engineer, writes that many of the distributaries of the Lower Ganga are nothing but artificial canals modified by natural riverine processes. A very advanced people known as Gangarides or Gangaridaes inhabited Lower Bengal (Basu 1989) and it was not unnatural for a civilized agrarian society to construct artificial canals for irrigation purposes (Bhattacharyya 1998, 2000, 2011). Indian historical records and reports are full of descriptions of such water management policies and programs. An inscription of Rudraman 1 on the Girner rock in Kathiawar records the construction and repair of an artificial lake Sudarsana by successive viceroys of the Maurya Chandragupta (320–290 BC). The lake was perfected under the Maurya Emperor Asoka (260–222 BC) (Kotriah 1959). In South India, the Chola rulers (first century AD) were the innovators in the construction of reservoirs. The Cauvery River was a flood-prone river and king Karikola first introduced the concept of flood control measures by constructing dams and embankments (Sarava 1954). The construction of a dam by Karikola is mentioned in an inscription of the Shaka year 1277 (1355 AD). Several tanks and a few anicuts were constructed (Kotriah 1959) during the periods of Chalukya, Hoyasala and Kakatiya rulers (twelfth century AD). Before 1900, India had only 43 dams that were 15 m or more in height. To provide water to the city of Mumbai, earth dams were built at Vihar around 1860, followed by the Powai and Tulsi dams in 1879. To meet increased demand for water, the first masonry gravity dam at Tansa was built in 1883. High masonry weirs were built across the Hatmati River in Gujarat, at Dhupdal across the Gataprabha River, and the

Introduction

33

Khadakwasla dam (1870) was built across the Mutha River in Maharashtra to provide water to the city of Pune. In 1897 the Periyar dam (54 m) was constructed across the west flowing Periyar River to divert waters through a tunnel cut through ridges into the east flowing Vaigai basin to irrigate an arid area. This classical diversion of west flowing rivers to the east brought prosperity to areas in the eastern watershed. Encouraged by the fruitful results, India constructed more dams, such as the Wilson, Gangapur, and Bhatgar in the state of Maharashtra. Of these, the Wilson dam (82 m, 1926) was the highest. In the south, India built the Krishnaraja Sagar dam across the Cauvery for irrigation in Mysuru. The second dam across the Cauvery was the Mettur dam (70 m, 1934) constructed in the Madras (now called Chennai) Presidency (CBIP 1991). In the early period, India constructed most of the dams to form storage reservoirs to circumvent the effect of seasonal variations in water flow and to provide water for irrigation. India included hydropower development from these reservoirs as an additional benefit. In the later period, with hydropower development assigned a top priority, India made efforts to include power generation in almost all the major irrigation projects taken up in the last 20 years or so (CBIP 1991). Since independence in 1947, India has trained several rivers throughout the country to reduce flood risk and enhance irrigation and power generation. India has launched several multipurpose projects. The Damodar Valley Corporation (DVC), with a sequence of four dams and four more in the pipeline, opened its doors on July 7th, 1948, following the model of the Tennessee Valley Authority (TVA) of the United States. Engineers constructed dams such as Maithon, Panchet, Tilaiya, and Konar, on the Damodar and its tributaries. The DVC dams are between 45 and 60 m high. The Konya dam (103 m), completed in 1961, was the first dam above 100 m in height. It was never much in the news, however, since work on a giant 226 m high dam (Bhakra) had started 8 years before work was begun on the Konya. The Bhakra Nangal dam was commissioned in 1963 on the Sutlej and the Hirakud on the Mahanadi was commissioned in 1957 with its reservoir area extending over 727 km2. In 1966, construction work commenced on the 169 m arch dam, the Idukki in Kerala. The Tungabhadra dam on a tributary of the Krishna, the Chambal reservoir on the Chambal, and the Kosi reservoir on the Kosi have been completed. The Tehri dam is higher than the Bhakra. Several dams, such as the Sriram Sagar, Srisailam and Sardar Sarovar, have reservoirs which exceed that of the Hirakud in size (Rangachari et al. 2000). To develop renewable water resources, India needs more dams like Sardar Sarovar dam recently inaugurated in India on September 17, 2017. The Sardar Sarovar Project, one of the largest water resources projects in India covering four major states of Maharashtra, Madhya Pradesh, Gujarat, and Rajasthan, with the dam’s spillway discharging capacity of 30.7 105 s3, would be third highest in the world (Plate 1.2). The Narmada Main Canal would be the largest irrigation canal in the world, with 1,133 m3s (40,000 s3) capacity at the head regulator, and 532 km in length. The dam will be the third highest concrete dam (163  m) in India, after Bhakra (226  m) in Himachal Pradesh and Lakhwar (192  m) in Uttar Pradesh. This dam will rank as the second largest in the world with an aggregate volume of 6.82 M m3 after Grand Coulee Dam (Plate 1.1) in the United States with a total volume of 8.0 M m3. This dam will be the third in the world with its spillway discharging capacity of 85,000 m3/s; the first two are Gazenba (1.13 105 m3/s) in China and Tucurri (1.0 105 m3/s) in Brazil.

34

Reservoir Sedimentation

PLATE 1.2 The Sardar Sarovar Dam, a gravity dam on the Narmada River near Navagam, Gujarat in India, is one of the largest dams in the world. The gross storage capacity of the reservoir is 0.95 M ha m (7.7 million acre-feet), while live storage capacity is 0.58 M ha m (4.75  million acre-feet). The dead storage capacity below minimum draw down level is 0.37 M ha m (2.97 million acre-feet). The reservoir would occupy an area of 37,000 ha and would have a linear stretch of 214 km of water and an average width of 1.77 km. (Source of Photographs: India: WRIS.)

The National Register of Large Dams (NRLD) in India is a compilation of dams in the country based on information received from the State Government/Authority concerned. In NRLD (CWC 2015b) the definition of large dams is the same as that given by the International Commission on Large Dams (ICOLD). The International Commission on Large Dams (ICOLD 1984, 2010) defines a large dam as a dam well above 15 m in height (from the lowest general foundation to the crest). However, even dams between 10 and 15 m in height could be classified as large dams, provided the volume of earthwork exceeds 0.75 M m3 and the reservoir capacity exceeds 1 M m3 or the maximum flood discharge exceeds 2,000 m3/s. Out of 58,519 large dams around the world, the top five dam-building countries account for more than 70 percent of all large dams worldwide. Over 23,842 of these dams are in China alone. Other countries among the top five dam building nations (Table 1.8) include the United States with over 9,265 large dams, India with around 5,190 large dams, and Japan with 3,113 large dams as per record of ICOLD (2015). Indian large dams constitute around 9 percent of the world dam population. About 80 percent of these dams are less than 30 m high and only about 1 percent of dams are major dams with height above 150 m (Gupta 1998). There are 69 (completed and under-construction) dams in India in the category of Dams of National Importance (CWC 2015b). Figures 1.13 through 1.15, and Appendix 1A and 1B show decade-wide and state-wide distribution of large dams (completed and under construction) in India. There are about 450 barrages and a series of canals and weirs to facilitate irrigation (Table 1.9, Plates 1.3 and 1.4).

35

Introduction

TABLE 1.8 Top Five Countries by Number of Large Dams ICOLD World Register of Dams 1998 1,855 6,375 4,011 1,077 1,187 10,918 25,423

Country China United States India Japan Spain Others Total

Other Sources 23,842 9,265 5,190 3,113 1196 15,913 58,519

Percent to Total Dams 41 16 9 5 2 27 100

5,000 4,500 4,000 3,500 3,000 2,500 2,000 1,500 1,000 500 0

4,877

1,264

499

631

386

0

0

313

0

0

n

er nd

om lc ta To

co

pl

ns

tr

et

uc

ed

ta no n io ct

ru st

tio

va

da

ila

m

s

bl

yo be d an

01 20 on fc ar o Ye

Time in decades

e

nd

00 –2 91

19

–1

99

0

98

81 19

–1

–1

97

71 19

61 19

–1

96

0

95 –1

198

U

234

51 19

to

19

01 19

p U

1,294

304

67

00

No of large dams

Source: ICOLD.

FIGURE 1.13 Distribution of Large Dams in India (Decade-Wise). (Data source: CWC, 2015b.)

1.6.1

classification of reservoirs

In 1966, the Fish Seed Committee of the Government of India classified all water bodies of more than 200 ha in area as reservoirs (Sugunan 1995). While assigning the water bodies of the state of Karnataka, David et al. (1974) considered impoundments above 500 ha as reservoirs and named the smaller waterbodies as irrigation tanks. The former U.S.S.R. classified reservoirs of up to 10,000 ha area as small reservoirs. In the United States, reservoir size ranges from 0.1 ha to several hectares (Bennet 1970; Sugunan 1995). China classifies reservoirs based on storage capacity (Lu 1986). Water bodies holding more than 100 M m3 of water are classified as large reservoirs, those holding 10 to 100 M m3 of water as medium, and those with 0.1 M to 10 M m3 as small reservoirs. Assuming an average depth of 10 m, small reservoirs of China are in the size range of 10–1,000 ha (Sugunan 1995). Records of the Government of India

36

Reservoir Sedimentation West Bengal, 29 Uttarakhand, 16 Telengana, 162 Tamil Nadu, 116

Uttar Pradesh, 115

Other states, 27

Andhra Pradesh, 142 Bihar, 24

Chhattisgarh, 248

Rajasthan, 201 Punjab, 14

Himachal Pradesh, 19

Orissa, 199

Gujarat, 619

Jammu & Kashmir, 14 Jharkhand, 50

Karnataka, 230

Maharashtra, 1,693 Madhya Pradesh, 898

Kerala, 61

Other states include: Andaman and Nicobar Island-2 Arunachal Pradesh-1, Assam-3 Goa-5, Haryana-1, Manipur-3, Meghalaya-8, Nagaland-1, Sikkim-2, Tripura-1

FIGURE 1.14 State-Wise Distribution of Large Dams (Completed) in India. (Data source: CWC, 2015b.)

West Bengal, 1 Uttarakhand, 9 Uttar Pradesh, 15 Rajasthan, 10 Punjab, 2 Orissa, 5 Manipur, 1

Mizoram, 1 Assam, 1 Andhra Pradesh, 25

Telengana, 20

Arunachal Pradesh, 3 Bihar, 2 Chhattisgarh, 10 Himachal Pradesh, 1 Gujarat, 13 Jammu & Kashmir, 3 Jharkhand, 29 Karnataka, 1 Kerala, 1

Maharashtra, 152

Madhya Pradesh, 8

FIGURE 1.15 State-Wise Distribution of Large Dams (Under Construction) in India. (Data source: CWC, 2015b.)

37

Introduction

TABLE 1.9 Water Resources Assets Large dam Major and Medium Irrigation Projects Barrages in India Hydroelectric Power Stations in Operation

5,190+ 2,700+ 450+ 1,235+

Source: India-WRIS.

PLATE 1.3 Rhondia Weir on the Damodar River. The Damodar canal system opened in 1933.  Water from the main river, Damodar was admitted into the canal with the help of a weir at Rhondia, known as the Anderson Weir near Panagarh of Barddhaman District. It has a length of 1,143 m. The main Damodar canal is 42.55 km with a branch canal of 34.51 km and a network of distributaries and village channels totaling a length of 344.78 km. (Source of Photographs: Kumkum Bhattacharyya, 21 December 2000.)

classified reservoirs as small with areas of less than 1,000 ha, medium with an area of 1,000–5,000 ha, and large with an area of more than 5,000 ha (Srivastava et al. 1985; Sarma 1990). The word tank in India is often loosely defined and used commonly to describe some of the small irrigation reservoirs. India designated many small humanmade lakes as tanks. There is no uniform definition of tanks. In the eastern states of West Bengal and Odisha, ponds and tanks are interchangeable expressions, while in states like Andhra Pradesh, Karnataka, and Tamil Nadu, tanks refer to a section of irrigation reservoirs, including small and medium-sized water bodies. In fact, some of the tanks in Tamil Nadu and Karnataka are much bigger than reservoirs like Aliyar or Tirumoorthy (Sugunan 1995) which have gross storage capacities of 112.754 and 54.8 M m3, respectively (CBIP 1987). The human-made lakes hold great potential for inland fisheries development and fish yield optimization from these reservoirs has attracted attention (Sugunan 2000).

38

Reservoir Sedimentation

PLATE 1.4 Durgapur Barrage on the Damodar River. A high diversity organization known as the Damodar Valley Corporation (DVC) came into existence on July 7, 1948 as a River Basin Organization (RBO) in India and proposed four multipurpose dams, and a barrage on the Damodar River, a subsystem of the Ganga River, India. The DVC constructed Tilaiya and Maithon Dams on the Barakar River, a tributary of Damodar, in 1952 and 1957, respectively, Konar Dam on the Konar Tributary in 1955, and the Panchet Dam on the Damodar River itself in 1959. The construction of a barrage on the Damodar River, a subsystem of the Ganga, at Durgapur started in 1952 and inaugurated in 1955 and subsidiary structures were completed by 1958. The barrage is about 692.20 m long. The main canal on the left bank is 137 km and the main canal on the right bank is 89 km in length. Branch and minor canals, distributaries, and drainage channels are about 2,270 km in length. (Source of Photographs: Irrigation & Waterways Dept. Govt. West Bengal, www.wbiwd.gov.in.)

In the United States, Canada, India, and China, the term dam refers to the dam structure and the term reservoir refers to the storage space upstream of the dam to store water. In Africa and Australia, the term dam refers to both the structure and the storage space upstream of the dam structure for storing water (Annandale 2013). The distribution of dams by number across India is highly uneven, depending on the topography of the states. The peninsular Highlands and the Himalayan Ranges have many suitable locations. Heights of dams also differ according to location; some Himalayan states have few dams but they are very large. Appendix 1B shows the distribution of dams by state.

1.6.2

effects of Dams anD reservoirs

Rivers adapt to the changes imposed by storage reservoirs and dams by adjusting to a new quasi-stable form. The presence of these control structures on rivers disrupt its equilibrium, leading to a series of changes in the fluvial system. In such a channel, water stored behind a dam and gradually released results in marked reduction in the magnitude and frequency of peak streamflow, disturbing the stable channel equilibrium as well as the flow regime (Petts 1984; Williams & Wolman 1984; Chien 1985; Kondolf 1997; Kondolf & Batalla 2006; Magilliigan & Nislow 2001, 2005; Chin et al. 2002; Bhattacharyya 1998, 2000, 2002, 2011; Graf 2006; Bhattacharyya & Wiley 2014). Dolan et  al. (1974) noted a 60 percent reduction in the magnitude of mean annual flood on the Colorado River below the Hoover Dam. Williams and

Introduction

39

Wolman (1984) observed that average annual peak discharges from 21 sites from the U.S. Geological Survey decreased from 3 percent to 91 percent of their pre-dam values averaging about 39 percent. Chien (1985) recorded that the Guanting Reservoir on the Yellow River, China, has reduced peaks by 78 percent from 3,700 to 800 m3/s. The flood peaks on the Sanmenxia Reservoir reduced from 12,400 to 4,870 m3/s, while the duration of mean daily flows (1,000–3,000 m3/s) increased from 130 days a year to 204 days a year. Kondolf and Batalla (2006) assembled hydrologic data on 14 major rivers in Sacramento–San Joaquin River system and analyzed changes in flow regime due to reservoir regulation and diversion. They calculated the Impounded Runoff (IR) index, expressed as “ratio of reservoir capacity divided by mean annual runoff” as per Batalla et al. (2004), which is 0.8 on the Sacramento and 1.2 on the San Joaquin Rivers, much higher than rates found in humid Atlantic climate regions. As a result of these high levels of impoundment, the overall magnitude and seasonal distribution of flows have changed significantly. Flood frequency analysis reveals progressive reduction in annual peak flow. The Q2 declined on average 53 and 81 percent in the Sacramento and San Joaquin River basins, respectively, with an average reduction of 67 percent (Kondolf & Batalla 2006). Bhattacharyya (1998, 2000, 2011) and Bhattacharyya and Wiley (2014) have observed that since the dam construction in 1957–1958, the average peak streamflow at Rhondia on the Damodar River, a subsystem of the Ganga, decreased to 3,607 m3/s in the post-dam period from the pre-dam flow of 8,413 m3/s and the pre-Rhondia (1823–1917) flow of 11,651 m3/s. Post-dam hydrographs show decreased monsoon discharges, and a shifting of peak flow from July to August to September, although there were again large interannual differences driven by variation in monsoonal precipitation. The river flow at Rhondia on the Damodar substantially reduced to an average 23 percent of catchment precipitation by both increased evaporation from the reservoirs and increased consumptive use of the stored water during dry periods (Bhattacharyya & Wiley 2014). Dam construction has numerous impacts on the downstream channel capacity (Wolman 1967; Petts & Lewin 1979; Chin et al. 2002; Bhattacharyya 1998, 2000, 2011; Bhattacharyya & Wiley 2014). For the Damodar River, the transport capacity of the river has reduced, the frequency of bank full events today is again like that observed in the pre-dam period. Numerous studies have been carried out to describe a drastic decrease in sediment volumes released from a reservoir due to the trapping of sediment in reservoirs. Kondolf et  al. (2014) reported that “we can think of the sediments accumulating in reservoirs (with negative consequences there) as ‘resources out of place,’ because these same sediments are desperately needed by the downstream river system to maintain its morphology and ecology, as well as for replenishing vital land at the coast.” Releasing of sediment-starved water leads to changes in channel cross-section, bed particle size, downstream bank erosion, and channel pattern and roughness (Williams & Wolman 1984; Chien 1985; Kondolf 1997; Hadley & Emmett 1998). According to Williams and Wolman (1984), the trap efficiency of large reservoirs is commonly greater than 99 percent in the United States. Andrews (1986) stated that below Flaming Gorge Dam on the Green River in the USA, tributaries have replenished the sediment supply within 68 miles downstream.

40

Reservoir Sedimentation

Changing patterns in flow regime and sediment supply have a dramatic effect on channel morphology, since these are two of the main controlling factors. The most common response of the river channel downstream is degradation due to large amounts of clear water released from most reservoirs. The moderately clear water releases can also be responsible for eliminating complete surface layers from the riverbed, if they are composed of finer materials, and thereby uncovering coarser layers (Williams & Wolman 1984; Chien 1985). Chien (1985) stated that after the completion of the Sanmenxia dam, the average bed degradation was between 0.6 m and 1.3 m during the first 4 years of storage operation. Williams and Wolman (1984) reported much greater impact below the Hoover dam on the Colorado River in the United States, where the maximum degradation 13 years after the completion of the dam was 7.5 m. The maximum degradation in most cases will occur directly below or near the dam, as in the case of High Aswan Dam for which the maximum degradation was 0.7 m (Schumm & Galay, 1994). Observations of some examples showed a reduction in channel width over the years. Murphy and Randle (2004) and Murphy et al. (2005) expanded upon the pioneering investigations of Williams (1978) in the case of the River Platte in state of Nebraska, in the United States. He reported that during the nineteenth century, the river channel, which was several kilometers wide at one period, reduced to only 10 percent to 20  percent of its previous width. The Rio Grande River below the Elephant Butte Dam in New Mexico, United States, was not a braided river prior to the operation of the dam. Since the Elephant Butte Dam began operation, this channel narrowed by as much as 90 percent (Everitt 1993). On the Trinity River, California, United States, construction of the Trinity Dam in 1960 reduced the 2-year flow from 450 to 9  m3/s. Due to dramatic changes in the flood regime, the encroachment of vegetation and deposition of sediment has narrowed the channel by 20 percent to 60 percent of its pre-dam width (Wilcock et al. 1996). Graf (2006) observed the shrinkage of the entire assemblage of functional surfaces associated with the channel while studying the geomorphic effects of the hydrological change of the Great Plains and Ozark-Ouachita River. In the case of the Damodar River, the average width of a specific section, observed at the beginning of the twentieth century (1930), decreased to 70 percent of the average width in 1854. The last 70 years have seen even more rapid narrowing, resulting in width that is only 60 percent (approximately) of the initial value in 1854 (Bhattacharyya 1998, 2000, 2011, 2016b). Dams pose threats to river basin hydrology as well as ecology. Large scale hydrological alteration includes deterioration and loss of river deltas and adjacent wetlands (Rosenberg et al. 1997; Syvitski et al. 2009), changes in sea-level (Vorosmarty & Sahagian 2000; Vorosmarty et al. 2003), as well as deterioration of irrigated terrestrial environment and associated surface water (McCully 1996; Rosenberg et al. 2000). Vorosmarty et  al. (2010) observed that dams and reservoirs affect biodiversity by inundation, flow manipulation, and fragmentation of habitat. Dams also alter water temperature and the amount of dissolved oxygen and nitrogen. Inundation disrupts the normal source characteristics of natural terrestrial and aquatic habitats for greenhouse gases (CO2 and CH4) and leads to the production as well as emission of large quantities of gases contributing to global warming potential (St. Louis et al. 2000). Large dams act as a primary destroyer of fisheries and lead to the extinction of

Introduction

41

species and overall losses of ecosystem resources (Postel 1998). Vegetation cover in and along channels downstream from the dams remained either the same or, in most cases, increased following dam closure. Williams and Wolman (1984) found that 7 out of the 10 rivers they studied, that previously had bare riparian zones, gained a 50 percent vegetation coverage after dam closure, some having as much as a 90 percent coverage. Vegetation increases are usually a result of channel narrowing (Kondolf & Matthews 1993), the decrease in high flows, and the increase in low flows (Hadley & Emmett 1998). Thus, alteration of the hydrologic regime by dams allows vegetation that floods would otherwise remove to intrude in the stream channel, allows the establishment of non-native species of fish and vegetation, and, in some instances, causes fine sediment to build up in the channel downstream (Knighton 1998; Minear 2002). After the construction of a dam, the river searches for a new dynamic equilibrium. Sediment starvation and high velocity water may cause lowering and scouring of a riverbed. Rivers downstream from dams initially adjust by channel degradation. A river will scour and degrade its channel bed as the sediment-depleted water emerging from the dam starts to replenish its sediment load (Williams & Wolman 1984). Since dams trap sediment, water released by dams does not contain sediment and is termed hungry water for its tendency to strip sediment from the downstream channel (Kondolf 1997). The stripping of salmon spawning gravel from river channels below dams has been a major issue in California for many decades and has necessitated expensive mechanical gravel sedimentation (Kondolf et al. 1991, 2014). Dams on the Damodar River reduced peak flow and the entire flow regime of the river on one hand, and converted, on the other hand, the unculturable barren sandbars or char lands into agricultural land making the area greener and habitable by people from flood-prone West Bengal and migrant people from erstwhile East Bengal (Bangladesh). Riparian communities are applying geomorphological knowledge to assess resource potentialities and hazard risks of the fluvial environment and converting the natural landscape into a hybrid landscape. The controlled rivers are now products of twin processes; quasi-natural hydro-geomorphic processes on the one hand and anthropogenic land utilization processes on the other (Bhattacharyya 2000, 2011). There are both positive and negative implications of large dams. Optimizing the benefits from large dams should highlight positive implications. We should also remember that economic development continues for the long term only if the riparian regime is ecologically as well as socially sound (Saha 1981; Bhattacharyya 2011; Bhattacharyya & Wiley 2014). Gupta (1998) underscored the point that many environmentalists and non-governmental organizations (NGOs) played a very commendable, positive, and vital role in increasing the awareness of dam engineers and supporting them in planning environmentally sustainable dam projects. On the other hand, he mentioned negative projections by many individuals, such as “no more dams, dams and damage, dams are doomed, replace large dams by smaller dams, and total stoppage of all dams regardless of their stage of construction.” He added, “If these directives on dams would have strictly been followed during the twentieth century, there would not have been most of the existing, even well-planned, designed and constructed major dams and hydropower projects, providing the needed additional water sources, flood control, protection against droughts, and power generation around the world.”

42

Reservoir Sedimentation

He added that in the absence of specific dams, the relevant countries probably would have been several decades behind. One could imagine these countries retreating a generation from their present stage of development (Gupta 1998).

1.7

RATE OF SEDIMENTATION: NEED FOR ASSESSMENT

Sediment behind a dam is a universal phenomenon and is a common denominator in all dams. It has an impact on our planet’s continuously changing surface water (Pekel et al. 2016). Loss of reservoir capacity from sedimentation is difficult to counterbalance with the construction of new reservoirs, because the most feasible sites already have reservoirs (Murthy 1995; Morris & Fan 1998; Annandale 2013). In building a dam, accurate assessment of sedimentation rate is a vital component of project planning, as incorrect assessment of the rate of sedimentation undermines the very existence of the dam itself. As an example, decommissioning of the Sanmenxia reservoir occurred in 1964 after just 4 years following its completion because the level of sedimentation far exceeded the presumed level. Similarly, the storage capacity of the Bassano Dam on the Bow River in Alberta, Canada, narrowed down from 34 M m3 to 11 M m3, an alarming diminution of 66 percent in 60 years (Sud et al. 2001). In the United States, the subcommittee on Sedimentation of the Interagency Advisory Committee on Water Data started assembling sedimentation surveys for over 1,800 reservoirs. The result of this compilation is RESIS (Reservoir Sedimentation Information System) and this comprises nearly 6,000 surveys for 1,819 reservoirs across the conterminous United States (excluding Florida and Maine). Dendy et al. (1973) and Dendy and Bolton (1976) summarized reservoir sedimentation data through 1973. By relating reservoir properties to sedimentation rate, these authors provided a guide for estimating reservoir sedimentation worldwide. The Federal Interagency Sedimentation Committee (FISC) reported a summary of U.S. reservoir data in 1992 and Renwick (1996) summarized the database through 1975 and focused on sediment yield as related to the properties of contributing watersheds (Stallard et al. 2001; Mixon 2002). Stallard et al. (2001) reported on the updated Reservoir Information System (RESIS) database, referred to as RESIS-II, with an automated location program that attempted to match coordinate data from each of the reservoirs with approximately 75 percent success (Stallard et al. 2001; Minear & Kondolf 2009). A study by Dendy from the United States Department of Agriculture Sedimentation Laboratory, Oxford, Mississippi, found the following rates of loss of capacity for reservoirs in the United States (Sud et al. 2001): In 1,105 reservoirs with a capacity of less than 0.0123 M m3, the rate of loss of capacity was about 3.5 percent per year. In medium sized reservoirs with a storage capacity greater than 0.123 M m3, the median rate of loss of capacity was 1.5 percent per year. In large reservoirs with a capacity of 12.3 M m3 and more, the rate of loss was 0.16 percent per year. Since the percentage of larger reservoirs in the United States is greater, the rate of sedimentation is not indicative of the situation worldwide as a whole. Also, most of the world’s reservoirs are relatively young. The International Commission on Large Dams (ICOLD) reports the construction of about 58,519 dams over 15 m high worldwide. Outside of the United States, the construction of most reservoirs was in

Introduction

43

the past 50 years, including 93 of the world’s 100 largest dams. Because these reservoirs are young, the number of sites experiencing severe sedimentation problems is insignificant but increasing. Nevertheless, almost all reservoirs in the world are continuously accumulating sediment, and the number of reservoirs with severe sedimentation problems will grow fast as the world’s register of reservoirs ages (Morris 1995a), while the importance of such reservoirs increases. Around the world the search is on for ways to reinstate sediment flows (Kondolf et  al. 2014; Robbins 2017). However, the problem of siltation has been well known for centuries and Spanish dams dating back more than four centuries were built in bottom sluices to periodically wash down sediment (Morris 1995a). Almost 82 years ago, Stevens  (1936) published his most important paper titled “The Silt Problem” in the Proceedings of the American Society of Civil Engineers (ASCE). Two years later the Transactions of the ASCE published the paper along with 35 pages of discussion by nine contributors and the authors’ enclosure (Stevens 1936; Nordin 1991). Stevens recognized some of the sediment problems associated with the construction of dams and reservoirs on sediment-laden streams and issued a challenge to scientists and engineers to take on the necessary studies and research to resolve the concerns he raised. In the published discussion of Stevens’ paper, Bonner in 1936 stated: “the capital outlays will be amortized long before the sedimentation of the reservoirs seriously impairs their usefulness. When the time comes, any desirable restoration of capacity will be a problem for the engineer of that far distant day….” Nordin (1991) commented on Stevens’ paper and concluded that “Sediment problems associated with the construction of dams and reservoirs on sediment-laden streams generally cannot be solved; they have to be managed … stream flow is a renewable resource, but hydropower is not if the power depends on the storage of reservoirs that become filled with sediment. The conditions under which long-term storage capacity of a reservoir can be preserved indefinitely are rather restrictive, but clearly, where these conditions exist, the project should be designed to preserve that storage.”

1.8

RESERVOIR SUSTAINABILITY

Reservoir life expectancy linked to sedimentation is a measure of reservoir sustainability. This sustainability plays a significant role in future water utilization and now sediment trapping behind dams causing reduction in a reservoir’s storage capacity is threatening it (Graf et  al. 2010). Uncontrolled sediment accumulation is gradually inching towards making a storage reservoir the key unsustainable constituent of a modern water supply system. In the design and maintenance of most reservoirs, engineers gave little thought to sustaining reservoir functions as sedimentation slowly reduces capacity (Morris & Fan 1998; Annandale 2013). The concept of better management of water and sediment to sustain reservoir function needs to replace the concept of reservoir life limited by sedimentation (Rao et al. 2014). The continuous diminution in global net storage space resulting from a faulty water resource development paradigm needs to be addressed by considering whether reservoir storage space is a renewable or an exhaustible resource. Reservoir sedimentation management is economically feasible if we recognize the twofold nature of reservoir storage, that is, it can be either renewable or exhaustible, depending on design and operational decisions. To achieve long-term benefits, we need to

44

Reservoir Sedimentation

convert sediment reservoirs into sustainable reservoirs by changing the development paradigm through initiating adequate changes in the design and operation of every reservoir (Morris et al. 2008; Narasayya et al. 2012; Annandale et al. 2016). The United Nations (UN) appointed “The World Commission on Environment and Development” that published a report (1987), titled “Our Common Future” also popularly known as the Brundtland Report after its chair, Mrs. Gro Harlem Brundtland, the then Prime Minister of Norway. The report stated that “Sustainable development seeks to meet the needs and aspirations of the present without compromising the ability to meet those of the future.” The fundamental concept of sustainable development is that the welfare of future generations should logically figure into the decision-making process by emphasizing the importance of intergenerational equity (Morris et al. 2008, Annandale 2013, 2014). Acknowledging the importance of creating and maintaining reservoir storage sustainably, the World Bank previously developed the RESCON (REServoir CONservation) approach (Palmieri et  al. 2003) to facilitate rapid identification of technically sound and economically optimum reservoir sediment management strategies. It is important to incorporate reservoir sediment management techniques into the planning and design phases of dam projects to provide information on specific sediment management strategies to use in projects to ensure sustained benefits of reservoir over the long term (Morris et al. 2008, 2016; Annandale 2013, 2014; Annandale et al. 2016).

1.9

SCOPE AND ORGANIZATION

The objective of this book is to make an appraisal of the status of reservoir sedimentation and discuss measures to use for the effective management of sediment to prolong the operational life of reservoirs for maintaining the reliability of water supply. The goal is also to provide direct information for policy makers to enable them to manage dams in the best possible way to ensure the sustainability of water resources. This information can provide food for thought and lays the groundwork for retrospection of the effects of anthropogenic intervention through dams and reservoirs in the natural environment in the Anthropocene.

1.10

THE ORGANIZATION OF THIS BOOK

This book is broadly divided into seven different chapters each pertaining to an important theme. The first chapter is an introduction, providing an overview of the subject of this book and it also lays out the objectives and scope of the book. The second chapter discusses land degradation, sediment trapping by dams, and reduced sediment fluxes to world’s oceans due to human activities as well as global sediment flux since the late Jurassic (in pre-human conditions). The third chapter reviews the literature related to sedimentation and discusses the process of sedimentation and its impact, and measurement of sedimentation. It defines the study area, the data gathering process and sources of data, and methodology of study. The fourth chapter explains reservoir sedimentation characteristics. The  fifth

Introduction

45

chapter explains the key factors affecting reservoir sedimentation. The sixth chapter discusses various strategies to use to accomplish effective sediment management for extending the reservoir life. The seventh chapter concludes the book.

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Shiklomanov, I. A. 1993. World fresh water resources. In: P. H. Gleick (Ed.) Water in Crisis: A Guide to the World’s Fresh Water Resources. Oxford, UK: Oxford University Press, pp. 13–24. Shiklomanov, I. A. (Ed.). 1997. Assessment of water resources and water availability in the world. Background Report for the Comprehensive Assessment of the Freshwater Resources of the world. Paris, France: WMO/SEI. Shiklomanov, I. A. 1998. Global renewable water resources. In: H. Zebidi (Ed.) Water: A Looming Crisis? Proceedings of the International Conference on the World Water Resources at the Beginning of 21st Century (UNESCO, Paris, June 3–6, 1998): IHP-Y Technical documents in Hydrology, Vol. 18, pp. 3–14. Shiklomanov, I. A. 1998. World Water Resources: A New Appraisal and Assessment for the 21st Century. Paris, France: UNESCO. Shiklomanov, I. A. 2003. World water use and availability (Chapter-11). In: I. A. Shiklomanov and J. C. Rodda (Eds.) World Water Resources at the Beginning of 21st Century. (UNESCO Paris), Cambridge, UK: Cambridge University Press. Shiklomanov, I. A. & Rodda, J. C. (Eds.). 2003. World Water Resources at the Beginning of the 21st Century (UNESCO Paris). Cambridge, UK: International Hydrology Series, Cambridge University Press. Simons, D. B. & Şentürk, F. 1992. Sediment Transport Technology, Water and Sediment Dynamics. Littleton, CO: Water Resources Pubns. Srivastava, U. K., Desai, V. K., Gupta, V. K., Rao, S. S., Gupta, G. S., Raghavachari, M. & Vatsala, S. 1985. Inland Fish Marketing in India-Reservoir Fisheries, Vol. 4 (A&B), New Delhi, India: Concept Publishing Co. Cited in Sugunan, 1995. STAP: The Scientific and Technical Advisory Panel. 2012. Climate Change: A Scientific Assessment for the GEF. A STAP Information Document by N. H. Ravindranath, R. E. H. Sims, Ürge-Vorsatz, D., Beerepoot, M., Chaturvedi, R. K. & Neretin, L. Washington, DC: Global Environment Facility. Stevens, J. C. 1936. The silt problem: (with discussion by Messrs. Harry G. Nickle. E.W. Lane, Frank E. Bonner, Morrough P. O’Brien, Harry F. Blaney, W.W. Waggoner, N.C. Grover, and J.C. Stevens): Trans Am Soc Civil Eng 101: 207–288. St. Louis, V. L., Kelly, C. A., Duchemin, E., Rudd, J. W. M. & Rosenberg, D. M. 2000. Reservoir surfaces as sources of greenhouse gases to the atmosphere: A global estimate. Bioscience 50: 766–775. Sud, S. C., Kumar, R. & Saxena, P. K. 2001. Sedimentation of Bhakra reservoir and mitigation measures. In: S. P. Kaushish & T. S. Murthy (Eds.) Proceedings on Reservoir Sedimentation. New Delhi, India: Central Board of Irrigation and Power, pp. 137–147. Sumi, T., Okano, M. & Takata, Y. 2004. Reservoir sedimentation management with bypass tunnels in Japan. In: Proceedings of 9th International Symposium on River Sedimentation, ii. Yichang, China, pp. 1036–1043. Stallard, R. F., Mixon, D. & Kinner, D. A. 2001. RESIS-II: Making the reservoir survey information system complete and user friendly, paper presented at the Seventh Federal Interagency Sedimentation Conference, Subcomm. on Sediment., Reno, Nev. Stallard, R. F., Mixon, D., Kinner, D. A. & Worstell, B. 2001. RESIS-II: Making the reservoir survey system complete and user friendly: Proceedings of the Seventh Interagency Sedimentation Conference. Reno, Nev, Vol. 2, pp. IX9–IX11. Sugunan, V. V. 1995. Reservoir fisheries of India. FAO Fisheries Technical paper 345. Barrackpore, India: Central Inland Capture Fisheries Research Institute. (Accessed on January 25, 2003). Syvitski, J. P. M., Kettner, A. J., Overeem, I., Hutton, E. W. H., Hannon, M. T. G., Robert Brakenridge, G. R., Day, J. et  al. 2009. Sinking deltas due to human activities. Nat GeoSci 2(10): 681–686.

Introduction

53

Tejwani, K. G. 1984. Reservoir sedimentation in India-its causes control and future course of action. Water Int 9: 150–154. Thomas, T., Jaiswal, R. K., Galkate, R. V. & Singh, S. 2009. Estimation of revised capacity in Shetrunji reservoir using remote sensing and GIS. J Indian Water Res Soc 29(3): 8–14. Turner, A. G. & Annamalai. H. 2012. Climate change and the South Asian monsoon. Nat Clim Chan 2: 587–595. doi:10.1038/nclimate1495. Tyagi, A. C. 2003. State of India’s Water. Mexico city, Mexico: Third World Centre for Water Management. (Accessed on May 27, 2003). UNEP (United Nations Environmental Programme). 2001. India: State of the Environment, Ministry of Environment and Forest (MoEF, Government of India). USDA: U.S. Department of Agriculture, Natural Resources Conservation Service. 2012. Understanding Fluvial Systems: Wetlands, Streams, and Flood Plains. Washington, DC: USDA. Veltrop, J. A. 1992. The Role of Dams in the 21st Century Dams. Denver, CO: United States Committee on Large Dams. Verthoeven, J. T. A. & Setter, T. L. 2010. Agricultural use of wetlands: Opportunities and limitations. Ann Bot 105(1): 155–163. Vörösmarty, C. J. & Sahagian, D. 2000. Anthropogenic disturbance of the terrestrial water cycle. Bioscience 50: 753–765. Vörösmarty, C. J., Meybeck, M., Fekete, B., Sharma, K., Green, P. & Syvitski, J. P. M. 2003. Anthropogenic sediment retention: Major global impact from registered river impoundments. Global Planetary Change 39(1–3): 169–190. Vörösmarty, C. J., McIntyre, P. B., Gessner, M. O., Dudgeon, D., Prusevich, A., Green, P., Glidden, S. 2010. Global threats to human water security and river biodiversity. Nature 467: 555–561. Walling, D. E. 2006. Human impact on land-ocean sediment transfer by the world’s rivers. Geomorphology 79: 192–216. doi:10.1016/j.geomorph.2006.06.019. Wan, X. Y. 2005. Study on Scheduling of Water and Sediment in Reservoir on Sedimentladen River. Nanjing, China: HOHAI University. White, R. 2001. Evacuation of Sediments from Reservoirs. London, UK: Thomas Telford Publishing. White, G. F (Ed.). 1977. Environmental effects of complex river development. Papers from a symposium of the International Geographical Union. Boulder, CO: Westview Press. Wilcock, P. R., Kondolf, G. M. Matthews, W. V. & Barta, A. F. 1996. Specification of sediment maintenance flows for a large gravel-bed river. Water Resour Res 32(9): 2911–2921. Willcocks, W. 1930. The Overflow Irrigation of Bengal, Lectures on the Ancient System of Irrigation in Bengal and its Application to Modern Problems. West Bengal, India: Calcutta University. Williams, G. P. 1978. The Case of the Shrinking Channels—The North Platte and Platte rivers in Nebraska. U.S. Geological Survey Circular 781. Washington, DC: U.S. Government Printing Office. William, G. P. & Wolman, M. G. 1984. Downstream effects of dams on alluvial rivers. U.S. Geological Survey Professional Paper 1286. Washington, DC: United States Government Printing Office, 83pp. Wolman, M. G. 1967. Two problems involving river channel changes and background observations. Northwest University Stud Geograp 14: 67–107. WRIS: Water Resources Information System of India. India’s water wealth. http://india-wris. nrsc.gov.in/wrpinfo/index.php?title=India%27s_Water_Wealth. (Accessed on August 23, 2016, November 30, 2016, October 8, 2017). WRIS: Water Resources Information System of India. Water Resources at a Glance 2011 Report, CWC, New Delhi, India. http://www.cwc.nic.in.

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Wu, B. M., Wang, G. & Xia, J. 2007. Case study: Delayed sedimentation response to inflow and operations at Sanmenxia Dam. J Hydr Engr, ASCE 133(5): 482–494. doi:10.1061/ ASCE0733-94292007133:5482. Xiangke, L. 1986. A review of reservoir fisheries in China. FAO Fisheries Circular, No. 803, 37p. Cited in Sugunan, 1995. Xiutao, W. 1986. Environmental impact of the Sanmen George project. Water Power Dam Const 38(11): 23–24. Yuan, H., Qi Shi, Q., Xiaoying, L., Jinming, X., Dan, L. & Hui, Z. 2015. Sediment management decision making of the Sanmenxia reservoir based on RESCON model. Afr J Agricult Res 10(24): 2332–2443. Zhou, Z. 1993. Remarks on Reservoir Sedimentation in China. pp. 153–160. In: S. S. Fan and G. Morris (Eds.) Notes on Sediment Management in Reservoirs: National and International Perspectives. Washington, DC: Federal Energy Regulatory Commission cited in Morris and Fan, 2009.

2

Land Degradation and Sediment Fluxes in the Anthropocene

2.1 LAND DEGRADATION DUE TO HUMAN ACTIVITY Geological processes are persistently changing the face of the Earth (Van Loon 2001); however, Nobel Laureate Paul Crutzen and Eugene Stoermer in the Global Change Newsletter 2000 (Crutzen & Stoermer 2000) articulated the concept that humans have also altered geological and geomorphological processes on Earth’s surface and are an integral component of the Earth system as a whole, and we are living in a new epoch, the Anthropocene. The Global Change Open Science Conference held in 2001 in Amsterdam and jointly organized by the International Geosphere-Biosphere Program (IGBP), the International Human Dimensions Program on Global Environmental Change (IHDP) and the World Climate Research Program (WCRP) marked the beginning of a new era for the IGBP as stated in Global Change Newsletter (2015). The Amsterdam Declaration stated explicitly that anthropogenic forces were equivalent to some of the great forces of nature in their magnitude and impact as mentioned by Moore et al. (2001). But way back in 1864, Marsh forewarned that irrational treatment of the environment by human beings might destroy the very base of subsistence of human society (Marsh 1864). Vernadski (1926) also formulated this concept at a time when human-environmental interaction was very limited (Meybeck 2003). Professor Jan Zalasiewicz from the University of Leicester’s Department of Geology said that the Anthropocene is an epoch-making phenomenon of our planet. It has come into being on a massive scale due to the significant human impact in ways that have no precedent in the 4.54 billion years of Earth’s history (Zalasiewicz et al. 2017). Anthropogenic processes rather than natural processes control components in different parts of the world today (Turner et al. 1990; Misserli et al. 2000), showing a marked paradigm shift in geomorphology from structural to applied and environmental to the emergence of the concept of Anthropocene (Bhattacharyya 2011). This paradigm shift has led to the suggestion that the current geological epoch be renamed Anthropocene in place of Holocene (Crutzen & Stoermer 2000; Zalasiewicz et al. 2008). At the beginning of the Holocene, that is, the last 11,700 years of the Earth’s history, the time since the end of the last ice age, there was a transition from food appropriation to food invention due to increasing human impact on the environment. Since then, human influence on the environment has only expanded (Ter-Stepanian 1988), with a large-scale conversion of forest-cover areas to agricultural areas, leading to augmented soil erosion.

55

56

Reservoir Sedimentation

Major civilizations in the world developed and matured along river banks because rivers provided freshwater and their valleys provided fertile lands for farming and raising cattle. The first three major civilizations that flourished about 5,000  years ago were those of the Harrapans in the Indo-Gangetic Plain, the Egyptians in the Nile Valley, and the Sumerians in Mesopotamia (Easton 1964; Biswas 1970). Open villages signified a degree of rudimentary civilization, with some of the social skills and discipline the word entails, by not later than 5000 BC in the foothills of northern Iraq, by Catal Huyuk near Konya in southern Turkey in 7000  BC, and by agricultural settlements at Mehrgarh (also about 7000  BC) on the Bolan River in the Indian subcontinent (Mishra 1995). Rivers have always historically been the freshwater source of choice throughout the world as the water flowing in them is continually replenished on a regular basis (Annandale 2013). Fertile soils have always been the foundation of prosperous civilizations with agricultural expansion on good land, with increasing population growth, followed by further agricultural growth onto marginal land, ultimately leading to soil erosion, decreasing agricultural productivity, threat to food security, and often societal collapse and migration (Montgomery 2007). These societal collapses can be traced to the human impact on the environment leading to the degradation of land on which they subsisted (Diamond 2005).

2.1.1

lanD DegraDation

Land can be defined as a complex, multi-component natural entity that develops a resource base when used for a specific reason or reasons. Considering this, land degradation has been described as “the reduction in the capability of the land to produce benefits from a particular land use under a specified form of land management” (Blaikie & Brookfield 1987). In the context of productivity, land degradation is the result of an incongruity between land quality and land use (Beinroth et al. 1994) and is described as a loss or diminution of soil energy (Blum 1998). Mechanisms that bring about land degradation include physical, chemical, and biological processes (ICAR 2010). Over the years, the intrinsic productivity of many lands has gradually decreased due to natural or anthropogenic activities (Conacher & Conacher 1995; Kudesia et al. 2009) and many lands have dramatically deteriorated due to soil erosion, accumulation of salinity, and nutrient depletion (Scholes & Scholes 2013). It is reported (Ranga Raju 2009) that the surface of the Earth is eroded at an average rate of 30 mm per 1,000 years. Naturally this erosion rate varies from year to year and from continent to continent. Chorley (1967) provided the average erosion rates in different continents (Table 2.1). Global approximations show a rising trend in degraded areas, with other areas becoming susceptible to various forms of degradation (Reich et al. 2001; FAO 2011; UNCCD 2013; Biswas et al. 2015). Land degradation has been a major global concern during the twentieth century and will remain a high priority on the international agenda in the twenty-first century. This priority is more so because of its impact on world food security and on the quality of the environment (FAO 1999; Eswaran et al. 2001; ICAR 2010). A complete, self-sustaining soil ecosystem is vital, especially in times of climate stress (Scholes & Scholes 2013).

Land Degradation and Sediment Fluxes in the Anthropocene

57

TABLE 2.1 Average Erosion Rates on Different Continents Continents Africa Asia Australia North and Central America South America Europe

Area in M km2

Erosion Rate in tons/km2 yr−1

29.81 44.89 7.88 20.44 17.98 4.67

72.2 208.0 43.4 113.0 148.0 75.0

Source: Chorley, 1967.

India, the seventh largest country in the world, has a total land area of 3,287,263 km2 (1,269,219 mi2, 328.73 M ha). Although India covers only 2.4 percent of the world’s total land area, it supports over 18 percent of the entire global population and 20 percent of the global livestock population. Degraded lands occupy a very large part of the total geographical area (TGA) of India despite considerable biodiversity (Anon 2000; CSWCRTI 2011). Land degradation, caused by natural phenomena and human activities such as wind and water erosion, water logging, soil erosion, and biophysical and chemical deterioration, is one of the major concerns in India (Sehgal and Abrol 1994; ICAR 2010; CSWCRTI 2011; Bhattacharyya et al. 2015). First, displacement of soil materials and their deposition and, second, in situ degradation largely brought about this land degradation. The loss of top soil and terrain deformation through water and wind erosion, as well as over-blowing of soil through wind erosion, belong to the first category. Chemical degradation, involving loss of nutrients and/or organic matter, salinization and pollution and physical degradation in the form of water logging, mass movement, landslides, compaction, crusting, and sealing belong to the second category (UNEP 2001; ICAR 2010). In India, areas under land degradation have been on the rise, particularly during the last few decades. Many researchers and organizations have assessed the severity and degree of soil degradation in India (Bhattacharyya et al. 2015, Table 2.2). The National Bureau of Soil Survey and Land Use Planning (NBSS & LUP 2004) estimated the degradation at 146.8 M ha of land. Water-induced erosion across the country is the primary reason for top soil loss and terrain deformation. Wind erosion is dominant in the western part of the country, causing a loss of top soil and terrain deformation (Sehgal & Abrol 1994; UNEP 2001; ICAR 2010). The varying degrees and types of degradation stem mainly from unsustainable use and inappropriate methods of soil and crop management in grassland cultivation (Kudesia et al. 2009; ICAR 2010; Bhattacharyya et al. 2015). Of India’s total geographical area of 328.73 M ha, with a cultivated area of 141 M ha, about 175 M ha of land requires soil preservation measures. The estimated total annual soil erosion for the entire country is 5,334 M tons, eroded every year from cultivable and forested land (Narayana & Ram 1983; Kumar 2004; The Hindu 2010). Indian rivers carry approximately 2,052 M tons of silt, of which nearly 480 M tons deposit in the reservoirs and 1,572 M tons wash away into the seas every year

58

Reservoir Sedimentation

TABLE 2.2 Extent of Land Degradation in India, as Assessed by Different Organizations Organization

Assessment Year

Reference

Degraded Area (M ha)

National commission on agriculture

1976

NCA, 1976

148.1

Ministry of agriculture—soil and water conservation division Department of environment National wasteland development broad Society for promotion of wastelands development National remote sensing agency Ministry of agriculture Ministry of agriculture NBSS & LUP NBSS & LUP (revised)

1978

MoA, 1978

175.0

1980 1985 1984

Vohra, 1980 NWDB, 1985 Bhumla and Khare

95.0 123.0 129.6

1985 1985 1994 1994 2004

NRSA MoA MoA NBSS & LUP NBSS & LUP

53.3 173.6 107.4 187.7 146.8

Source: Bhattacharyya et al. 2015.

(Das  &  Saikia  2013; Durbude 2014). These rates serve as a guide for developing measures for arresting the huge loss of productive soil (Narayan & Ram 1983; Samra & Sikka 2001). For comparison, the permissible value for soil erosion in the United States is 4.5 to 11.2 ton ha (Mannering 1981; Narayan & Ram 1983). In India, nearly 29 percent of the total eroded soil is permanently lost to the sea, while 61 percent is simply transmitted from one place to another and the remaining 10 percent is dropped in the reservoirs (Bhattacharyya et al. 2015). Decades ago, studies attempted to estimate soil erosion in India through available information on soil loss (Narayana & Ram 1983). Based on hydrometeorology data, land use, and catchment characteristics from 135 catchments spread evenly all over India, Garde and Kothyari (1985) estimated erosion rates from catchments. Maps show iso-erosion factors and iso-erosion rate for India. Studies have given the average erosion rate in tons/km2 yr–1 (Table 2.3) for 12 major rivers. For comparison of erosion rates in India with other rivers in different countries, studies have compiled and presented data from various sources (Holeman 1968; Chien et al. 1980) (Table 2.4). Erosion rates in Indian catchments are large compared to American river catchments. These high rates in India are comparable to erosion rates in the Red River (Vietnam) and the Irrawadi (Myanmar). El-Swaify et al. (1982) provided a comparison of the estimated annual soil erosion within the drainage basins of rivers of several tropical countries which shows that the drainage basins of India (Kosi, Damodar, and Ganga) have extremely high erosion values. Erosion rates in the Chinese and Indian river catchments are in general much higher than those in the United States (El-Swaify et al. 1982, Garde & Kothyari 1985; Narayayana 1987; Gupta et al. 2012). China and India are losing higher percentages of storage capacity annually because of low forest cover (China 16.5 percent and India 23 percent) and high erosion (Liu et al. 2002).

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Land Degradation and Sediment Fluxes in the Anthropocene

TABLE 2.3 Average Erosion Rates for Large River Catchments in India

River Indus Ganga Brahmaputra Sabarmati Mahi Narmada Tapi Luni Mahanadi Godavari Krishna Cauvery

No. of Points at Which Erosion Rates Are Considered 4 23 5 7 3 10 10 1 11 10 7 5

Catchment Area in 102 km2

Erosion Rate tons/km2 yr –1 (Garde and Kothyari 1985)

Erosion Rate tons/ km2 yr –1 (Narayan and Ram 1983)

32.13 86.15 18.71 2.17 3.76 9.88 6.69 0.001 14.16 31.28 25.0 8.79

1,673.1 2,450.6 2,342.2 880.4 544.5 937.8 889.5 314.9 1,276.6 1,135.6 1,162.9 1,172.9

329.0 680.2 2,512 386.6 587.8 621.2 1,524.4 71.08 695.9 253.03 387.28 288.3

TABLE 2.4 Average Erosion Rates for River Catchments in Other Countries River

Country

Catchment Area in M km2

Erosion Rate tons/ km2 yr –1

Yellow Yangtze Daling (Liohe) Ching (Tributary, Yellow river) Haihe (Yongdiu) Lo (Tributary, Yellow river) Mississippi Missouri (Tributary, Mississippi) Colorado Amazon Irrawadi Mekong Red Nile

China China China China China China U.S.A. U.S.A. U.S.A. Brazil Myanmar Thailand Vietnam Egypt

673.6 1,943 23.2 57.0 50.8 25.9 3,222.8 1,370.5 637.3 5,777 430 62.2 119.2 2,979.3

2,480 540.4 1,490 7,913 1,944 7,797.2 108.1 173.7 416.9 65.62 903.2 478.6 1,192.7 38.6

Source: Garde and Kothyari, 1985.

60

Reservoir Sedimentation

The iso-erosion rate map is a first approximate map of soil erosion rates for land use planning. Available maps on soil types, rainfall erosivity potential, slope, land use, forest vegetation, degraded land, sand dunes, and irrigation were used to prepare the map (Singh et al. 1992). Observed soil loss data for different land uses were collected from 21 research stations and watersheds under the Indian Council of Agricultural Research and other organizations in the country’s 20 different land resource regions (Gupta et al. 1970). Reservoir sedimentation data (CBIP 1981) and an irrigation map (CBIP 1984) were also used (Singh et al. 1992). These data sources were complemented by approximations of soil loss from empirical models such as the Universal Soil Loss Equation (USLE) (Wischmeier and Smith 1978). Iso-erosion rate lines were drawn based on these 21 observed and 64 estimated soil loss data points spread over different land resource regions, and superimposing the eight above-mentioned maps (soil, rainfall erosivity potential, slope, land use, forest vegetation, degraded land, sand dunes and irrigation) on 1: 6,000,000-scale maps. Singh et al. (1992) classified soil erosion rates into six categories and areas under various erosion classes are shown in Table 2.5. The annual water-induced erosion rate ranges from less than 5 M g/ha–1 yr–1 (2.2 tons/ acre) for dense forest, snow-clad cold deserts, and the arid region of western Rajasthan to more than 80 M g/ha–1 yr–1 (36 tons/acre) in the Shiwalik, that is, northeastern foothills of the Himalayas. Ravines along the banks of the Yamuna, Chambal, Mahi, Tapi and Krishna rivers, and in the shifting cultivation regions of Orissa and the northeastern states, revealed soil losses exceeding 40 M g/ha–1 yr–1 (18 tons/acre). The annual erosion rates in the Western Ghats coastal regions vary from 20 M to 30 M g/ha (9–13 tons/ acre). Erosion rates in the black soil region (vertisols) are generally 20 M g/ha–1 yr–1. Soil loss in the remaining parts of the country ranges between 10 M and 20 M g/ha–1 yr–1. The areas of most spectacular erosion are the severely eroded gullied lands along the banks of the Yamuna, Chambal, Mahi, and west-flowing rivers in Gujarat. Narayana & Ram (1983) summarized the characteristics of 18 river basins (Table  2.6). This table includes data on catchment areas and annual values of precipitation, runoff, El30 (annual erosion index), and sediment loads. The El30  values TABLE 2.5 Area under Different Classes of Soil Erosion by Water in India Soil Erosion Rate Range (M g/ha–1 yr–1)

Area (km2)

0–5 5–10 10–20 20–40 40–80 More than 80

801,350 1,405,640 805,030 160,050 83,300 31,895

Source: Singh et al. 1992.

Soil Erosion Class Slight Moderate High Very high Severe Very severe

61

Land Degradation and Sediment Fluxes in the Anthropocene

TABLE 2.6 Salient Hydrological Details of River Basins of India Catchment Area (M ha)

Annual Total Run-off (M ha. m)

Annual Precipitation (cm)

Annual EI30 (metric units)

55.01 42.20 17.50

116 122 286

489 510 1,089

586 470 210

11.21

21.79

279

1,064

252.22

6.69

1.97

78

354

101.98

9.88 3.76

4.01 1.18

121 83

508 372

61.37 22.10

2.17 32.19

0.37 1.23

76 38

347 213

8.39 22.88

32.13 8.10

7.69 4.35

56 147

277 598

105.70 65.69

14.16 4.97

7.07 1.72

146 111

594 471

98.54 30.27

31.28 25 14.49

11.54 5.78 2.53

110 81 82

467 365 368

79.15 96.82 41.78

8.79 3.51

8.46 0.95

99 91

429 400

32.31 18.44

118

496

River Basin

India

1. Ganga basin 2. Brahmaputra basin 3. Barakar and other rivers (DVC) 4. West flowing rivers below Tapi 5. Tapi including Kim 6. Narmada 7. Mahi including Dhadhar 8. Sabarmati 9. Luni and others of Saurashtra and Kutch 10. Indus 11. East flowing rivers between Ganga and Mahanadi 12. Mahanadi 13. East flowing rivers between Mahanadi and Godavari 14. Godavari 15. Krishna 16. Pennar and other east flowing rivers between Krishna and Cauvery 17. Cauvery 18. East flowing rivers below Cauvery Average

86.15 18.71 7.82

Outside India 18.18 39.29

Source: Gupta, 1975; Narayana and Ram, 1983.

Sediment Load (M tons)

62

Reservoir Sedimentation

TABLE 2.7 Land Degradation in India (Previous Estimate) Type of Degradation Water Erosion Wind Erosion Total Saline and Alkali Soils Water-logging Decline in soil fertility Total

Estimation (M ha) 148.9 13.5 162.4 10.1 11.6 3.7 187.8

Source: Sehgal and Abrol, 1994.

TABLE 2.8 Land Degradation in India (Present Estimate) Type of Degradation Water Erosion Wind Erosion Total Acidification Salinity Flooding Combination of factors Total

Estimation (M ha) 94.8 9 103.8 16 6 14 7 146.8

Source: Bhattacharyya et al. 2015.

for Gujarat and the DVC river basins are higher than 1,000 and those of the Ganga, Brahmaputra, Mahanadi, and other east-flowing rivers between the Mahanadi and Godavari are above 500 which is the average El30 (metric unit) for the country. The total sediment loads of the Ganga and Brahmaputra (annual values) are the highest and more than one-third of these 18 rivers carry sediment loads of 100 M tons or more. Tables 2.7 and 2.8 present the previous and latest estimates of land degradation respectively. The latest estimates of land degradation show (Table 2.8) that an area of about 146.8 M ha of degraded land includes 94.8 M ha solely accounted for by water-induced soil erosion, 16 M ha from acidification, 14 M ha from flooding, 9 M ha from wind erosion, 6 M ha from salinity, and 7 M ha from a combination of factors (Bhattacharyya et al. 2015).

2.1.2 extent anD causes of soil DegraDation by region Appendix 2A provides the magnitude of land degradation, as approximated by NBSS & LUP and the Indian Council of Agricultural Research (ICAR) (Tables 2.9 and 2.10).

3 0.22 4.32 2.11 1.6

Description

NWH = Northwest hills, NEH = Northeastern hills. Source: Bhattacharyya et al. 2015, CSWCRTI, 2011.

3 4 5 6

1 2

2

2.72 5.44 3.97 2.8 −1

4 0.76 8.51 4.34 1.74

Exclusively water erosion (>10 ton ha ) Water erosion under open forest (2.0 concentrations of hot spot in Zone 4b.

Reservoir Sedimentation Rate

151

FIGURE 4.12 Relationship between Catchment Area of Reservoir with (a) Average Annual Rate of Sedimentation in the Reservoir, and (b) Average Annual Rate of Sedimentation from 100 km 2 of Catchment Area.

152

4.8

Reservoir Sedimentation

SEDIMENT DEPOSITION IN A RESERVOIR

The actual rate of sediment deposition in a reservoir depends on many factors, such as trap efficiency of the reservoir, ratio of reservoir capacity to total runoff, gradation of silt, and method of reservoir operation. When storage begins, the reservoir trap efficiency is continuously reduced. The two dominant factors controlling the rate of silting in any storage reservoir are (1) the ratio of reservoir capacity to inflow, and (2) the content of sediment in the inflow (CWC 2015a). A reservoir with a small capacity-inflow ratio and small sediment content in the inflow might have the same average percentage loss of annual capacity as a reservoir having a large capacity-inflow ratio and large sediment content in the flow. When the capacity of a reservoir is more than its annual runoff, that is, its capacity-inflow ratio is more than 1, then, including the effect of seepage and evaporation losses, it is evident that water is rarely tripped over the dam, making the trap efficiency of these reservoirs close to 100 percent. If the operation is adjusted to allow for a major portion of inflow through the outlets, the trap efficiency may be brought to 60 percent with a capacity-inflow ratio of 1.7, and to about 90 percent under normal operating conditions (Murthy 1995; CWC 2001, 2015a). Table 4.13 presents the original and subsequent trap efficiencies of some of the reservoirs as per Brune’s trap efficiency curve. Garg and Jothiprakash (2010) estimated potential trapping efficiency using Brune’s (1953) graphical empirical method and assessed watershed sediment yield (silt index) indirectly from the silt contributing area, sediment deposition in a reservoir, and its trapping efficiency. Chaudhuri (2017) evaluated different temporal and spatial factors affecting sediment deposition in a reservoir and its distribution. A non-iterative processed empirical distribution model (NPEDM) and a linear regression trend model  (LRTM) are suggested to predict sediment distribution in 57  reservoirs in the United States and India. In the United States, trap efficiency in different reservoirs ranges from 69 percent to 98.5 percent, whereas the silt index ranges from 0.11 to 34.82 ha m/100 km2 yr –1 in different watersheds (Appendix 4F). Trap efficiency is observed to be 95 percent

TABLE 4.13 Trap Efficiency of Some of the Reservoirs (According to Brune’s Trap Efficiency Curve) Name of Reservoir Konar Idukki Kakki Balimela Bhakra Matatila Maithon Source: CWC, 2015a.

Name of State

Original Trap Efficiency (year)

Bihar Kerala Kerala Orissa Punjab Uttar Pradesh Bihar

97 percent (1955) 98.4 percent (1974) 98 percent (1966) 96 percent (1972) 99.8 percent (1996) 90 percent (1956) 96 percent (1955)

Latest Trap Efficiency (year) 92 percent (1996) 97 percent (1999) 96 percent (1999) 95 percent (1999) 95.5 percent (1996) 88 percent (1994) 95 percent (1994)

Reservoir Sedimentation Rate

153

or more in 35 reservoirs where their operative stage differs between 23 and 103 years. While evaluating the different factors affecting sediment deposition in reservoirs, factor wise correlation values between the annual rate of deposition and the corresponding influencing factors (a) mean annual precipitation depth, (b) mean annual reservoir inflow, (c) silt contributing area, and (d)  drainage area are observed  −0.351, 0.955, 0.985, and 0.955, respectively. Jain and Singh (2006) stated that these values were statistically significant even at the 99 percent confidence level and the corresponding coefficient of determination, that is, r2 , were 0.123, 0.912, 0.970, and 0.912, respectively (Chaudhuri 2017). Based on empirical experience on 57 reservoirs in the United States, Chaudhuri (2017) noted that silt contributing area and inflow entering the reservoir were the most influential factors for sediment deposition in reservoirs. The correlation and r2 values specify that silt contributing area and inflow incoming a reservoir are the most important effects on the sediment load of any reservoir. It is also important to note that the intensity of rainfall is more important than the total depth for detachment of soil particles which contribute in sediment deposition in reservoirs (Morgan 1995). Salas and Shin (1999) made a similar observation but the poor correlation and r2  values signify that mean-annual precipitation has a lesser direct impact on the sediment deposition in the reservoirs. Water (2001) also observed a similar weak correlation while studying the reservoirs in Britain. Dysarz et al. (2014) presented a comparison of the two approaches while modeling reservoir sedimentation in a lowland reservoir, the Stare Miasto reservoir on the Powa River of Poland. The first is the basic approach based on the sediment routing model described by several transport formulations. The second is a newer approach known as the Sediment Impact Analysis Method (SIAM). They mentioned that the idea of SIAM seems to be promising, although the method still needs some improvement. Instead, application of the sediment routing involves too much time-consuming computations for effective use in reservoir design and prediction of capacity changes due to sedimentation.

4.9

DISTRIBUTION OF SEDIMENT IN RESERVOIRS

In the past, it was believed that sediment was always deposited in the bottom elevation of the reservoir rather than being suspended throughout the full range of reservoir depth. Several factors, such as the amount of sediment load, size distribution, fluctuation in stream discharge, topography of the reservoir, stream valley-slope, vegetation at the head of the reservoir, location and size of reservoir outlets, and so on, control the location of sediment deposits in the reservoir (Murthy 1995; DVC 1997; CWC 2015a; Chaudhuri 2017). In a multipurpose reservoir, the variation in water level is significant to the deposition of sediment in the reservoir as well as its movement through the reservoir. At higher elevations of a reservoir, sediment first deposits in the live storage space, but when the reservoir is drawn down and succeeding storms follow, this sediment flushes down into the lower elevations of the reservoir, and eventually, find its way into the portion of the reservoir originally provided for dead storage (Murthy 1995). Table 4.14 gives the distribution of sediment observed in some of the important reservoirs. Balimela, Hirakud, Matatila, Konar, Nizamsagar, and Tilaiya reservoirs favor deposition in the upper reaches, while Bhakra, Panchet, Maithon, Pong, and Tungabhadra reservoirs show deposition in the middle reaches (CWC 2001, 2015a).

Top 10 percent of the reservoir depth 10 to 20 percent 20 to 30 percent 30 to 40 percent 40 to 50 percent 50 to 60 percent 60 to 70 percent 70 to 80 percent 80 to 90 percent Bottom 10 percent of reservoir depth

Percentage Depth

Bhakra 1 2 16.5 22 21.5 14.2 11 6.4 3.8 1

Balimela 25 11 9 8 7 7 8 12 8 5

TABLE 4.14 Vertical Distribution of Sediment Deposition Hirakud 29 5 4 4 4 7 9 14 14 10

Maithon 3.5 12.5 20 19.5 14.5 11 8.5 4.5 5 1

Matatila 42.1 3.5 6.8 5.8 7.9 8.1 9.1 11.2 3.4 2.1

Pong 6 6 16 30 20 9 7 3 2 1

Percentage Sediment Deposit Panchet 20 2 3.2 5 10.5 13.5 15 15.5 15 0.3

Konar 20 22 15 13 12.5 8 5 2 1.3 0.7

Nizamsagar 10.5 15 17 16.3 11.9 8.6 7 5.5 2 6

Tilaiya 22 21 15 12 9 7 5 4 3 2

Tungabhadra 1.3 5.7 7.7 10.8 13.2 16.3 19 13.4 8.6 4

154 Reservoir Sedimentation

Source: CWC, 2015a.

Top 10 percent of the reservoir depth 10 to 20 percent 20 to 30 percent 30 to 40 percent 40 to 50 percent 50 to 60 percent 60 to 70 percent 70 to 80 percent 80 to 90 percent Bottom 10 percent of reservoir depth

Percentage Depth

Upper Kolab 12 27 13 10 9 10 7 6.5 3.5 2

Ranapratap Sagar 1 1.5 2.5 3 6.5 10.5 25 35.5 10 4.5

TABLE 4.14 (Continued ) Vertical Distribution of Sediment Deposition

18.5 10 10 10 9 9 9 9.5 9.5 5.5

Bhadra 20 11 11 11 14.5 14.5 11 4 2 1

Bhima 45 43 5 3 1.5 1.1 0.8 0.3 0.2 0.1

0 0 0 0 0 10 38 29 13 10

Idamalayar 38 22 20 11 2.5 2 1.5 1 1 1

Upper Wardha

Percentage Sediment Deposit Durgapur

1 2 9 23 27 20 11.5 4 1.5 1

Salaulim

16 11.5 9 9.5 10 10 14 12.5 5 1.5

Dudhwa

0.08 0.05 0.03 0.32 0.49 7.56 14.8 19.92 22.96 33.82

Watrak

Reservoir Sedimentation Rate 155

156

Reservoir Sedimentation

Chaudhuri (2012) observed almost negligible deposition in the Maithon reservoir between the elevations (EL) 125.00 and 128.05  m up to the year of 1971 because of topographical features of the original reservoir bed. Sediment deposition increased slowly afterward within the EL 125.00 and 128.05 m. The observation for Panchet reservoir was similar with negligible deposition up to 1996 within EL 106.71 and 109.76 m due to the steeper slope of reservoir topography. Reservoir topography was changing continuously influencing the deposition behavior. The Elephant Butte Reservoir had a similar pattern of curves for the different survey years (Chaudhuri 2017).

4.10

DENSITY OF DEPOSITED SEDIMENT IN RESERVOIRS

Table 4.15 gives the density of deposited sediment for 21 reservoirs. It is obvious that the density is predominantly affected by the percentage of clay in the samples and that the density gradually increases with distance from the dam. Studies observed lower densities close to a dam under submerged conditions and higher densities in the upstream portions of the submerged area as well as in the exposed regions following TABLE 4.15 Density of Deposited Sediment in Reservoirs Name of Reservoir/State Nizamsagar (Andhra Pradesh) Konar (Jharkhand) Tilaiya (Jharkhand) Maithon (Jharkhand) Panchet (Jharkhand) Pong (Himachal Pradesh Matatila (Uttar Pradesh) Idukki (Kerala) Kakki (Kerala) Balimela (Orissa) Bhakra (Punjab) Matatila (Uttar Pradesh) Mayurakshi (West Bengal) Bhadra (Karrnataka) Idamalayar (Kerala) Upper Wardha (Maharashtra) Durgapur (West Bengal) Salaulim (Goa) Ranapratap Sagar (Rajasthan) Bhima (Maharashtra) Dudhawa (Chhattisgarh) Average of 21 reservoirs Source: CWC, 2015a.

Unit

Density

Mid Value

Kg/m Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3 Kg/m3

481–1,490 1,350–1,620 1,265–1,845 513–1,714 561–1,762 1,000–1,023 1,230–1,470 980–1,038 730–834 600–1,230 1,202–1,650 721–1,330 801–1,121 1,140–1,910 1,110–1,900 860–1,130 1,340–1,620 690–1,670 680–1,540 940–1,980 830–1,110 880–1,394

986 1,485 1,555 1,114 1,162 1,012 1,350 1,009 780 915 1,426 1,025 961 1,525 1,505 995 1,480 1,180 1,110 1,460 970 1,191

3

157

Reservoir Sedimentation Rate

the periodic drawdown of the reservoir. The data shows that factors such as reservoir operation and side tributaries washing into the main reservoir determine sediment density (CWC 2001, 2015a).

4.11

ANALYSIS OF DEPOSITED SEDIMENT

Appendix 4G presents grain size analysis of deposited sediment carried out (CWC 2001, 2015a) for several reservoirs. Clay/silt content is maximum near the dam and falls as one moves upstream of the reservoir. The percentage of sand is least near the dam and increases progressively while proceeding upstream.

4.12

ESTIMATED LIFE OF RESERVOIRS

The plan of a dam or a reservoir presumes a certain life for the dam or reservoir under the design life paradigm, perhaps 50 or 100 years, and planners design its capacity so that it continues, by and large, to deliver the benefits presumed in the project with due allowance for the loss in capacity due to silting and sedimentation. In practice, the capacities of many of the reservoirs have contracted too fast, challenging expectations due to heavier than predictable sedimentation occurring mainly because of land use changes in the catchment area, the failure to take adequate measures to control and diminish soil erosion, and for not adopting successful sediment management strategies. The Nizamsagar Reservoir in Telangana has lost 52  percent of its live capacity within just 37 years of its existence (Mohanakrishan 2001), and as much as 61 percent of its storage capacity within 62 years of its existence (CWC 2015a). The Baira Reservoir in Himachal Pradesh lost 84 percent of its gross storage by 2011. Table 4.16 gives the estimated life of some reservoirs. Studies TABLE 4.16 Estimated Life of Some Reservoirs Name of Reservoir Konar Ghetalsud Tenughat Tilaiya Dharoi Ghataprabha Linganamakki Idukki Kakki Jayakwadi Balimela

State

Year of Impoundment

Year of Last Survey

Jharkhand Jharkhand Jharkhand Jharkhand Gujarat Karnataka Karnataka Kerala Kerala Maharashtra Orissa

1955 1971 1970 1953 1976 1974 1964 1974 1966 1976 1972

1997 2001 2001 1997 2006 2000 2000 1999 1999 2000 1999

Source: CWC, 2015a; Agarwal et al. 2001.

Observed Rate of Sedimentation (m3/km2 yr –1)

Estimated Life

1,750 970 716 2,857 763 3,148 2,396 1,592 3,522 478 2,131

>135 >540 >322 >108 >133 >175 >150 >330 >330 >105 >177

158

Reservoir Sedimentation

calculated the life assuming that the rate of sedimentation in the year of last survey would continue (CWC 2015a; Agarwal et al. 2001). Graf et al. (2010) used data from the Army Corps of Engineers, U.S. Bureau of Reclamation, and U.S. Geological Survey (Reservoir Sedimentation Survey Information System II (RESIS II)) and examined the sustainability of United States reservoirs. The sustainability or life span of reservoirs varied by region, with the longest life expectancies in New England and the Tennessee Valley and the shortest in the interior west. In the Missouri and Colorado River basins, sedimentation rates and loss of storage capacity were highly variable in time and space. In the Missouri River basin, larger reservoirs had the longest life expectancies, with some more than 1,000 years, while smaller reservoirs in the basin had the shortest life expectancies, which are located particularly in the Kansas and Osage River basins, where they collect runoff coming from drainage areas with high sediment yields. The Colorado River basin provides a unique example for temporal variation in sedimentation because of its exceptionally long record of sediment transport recounting sediment yields from all its major sub-basins. In the Colorado River basin at the site of Glen Canyon Dam, sediment inflow dropped by half beginning in 1942 because of hydroclimate and upstream geomorphic changes. The estimated life expectancy of Lake Powell increased from 300 to 700 years, because of these changes (Graf et al. 2010). Minear and Kondolf (2009) predicted that total annual sediment accumulated in reservoirs in California, through 2008, is 2.1 G m3, declining the total capacity by 4.5 percent. About 120  reservoirs have capacities decreased to less than 25 percent of their original capacity and almost 190 reservoirs have less than 50 percent of original capacity remaining. About 200 reservoirs have likely lost more than half their initial capacity to sedimentation. As per availability of data (Utah Division of Water Resources 2010). Utah reservoirs are losing capacity from 4.1 percent per year to 0.02 percent per year, indicating a wide range in sediment accumulation rates. A High Country News (HCN) analysis of U.S. Bureau of Reclamation (USBR) data presents the most recent, publicly accessible, surveys for 8 of 11 Western states. The report shows that 35 USBR reservoirs have lost approximately 5.67 BCM or G m3 of storage capacity due to sedimentation. That is about 8 percent of their total storage, or enough water to supply at least 9  million households (Weiser 2011). Luo et al. (2011) estimated the life span of 421 dams in Japan and divided them into three groups which are under 100 years as Group 1, 100–500 years as Group 2, and over 500 years as Group 3. The life span in Chubu region, Hokkaido region, and Kyushu region had the shorter life span than other regions with 335, 473, and 559 years in average. In Chugoku region, there are eight dams with life spans over 5,000 years. The average slope of watershed is highly correlated with the life span of reservoirs.

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159

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5

Sediment Yield

5.1 SEDIMENT YIELD One of the most important measures pertaining to reservoir sedimentation is the amount of sediment transported to a specified point in a drainage basin over a defined period. This quantity is sediment yield and is expressed as the number of tons of sediment per unit catchment area per year (t/km2 yr–1). It is normal to have significant spatial and temporal fluctuations in the sediment yield from year to year in a specific catchment (Garde 1995; CWC 2001, 2015; Annandale 2016b). The factors affecting the sediment yield of a drainage area are rainfall and soil characteristics (for example, soil coverage, vegetation, geology, and apparent rocks), soil management (cultivation practices, grazing grass, forest management, building activities, and conservation measures), topography (geomorphology), nature of the drainage network (drainage density, slope, shape, size, and channel configuration), surface runoff, sediment features (for example, granulometric and mineralogical), channel hydraulics, and human disturbances (Durbude 2014). However, no single parameter or simple combination of parameters clearly explains the wide variability in global sediment yield (Morris & Fan 1998). Sediment yield also depends on a host of other factors: the size, shape, and slope of watershed; reservoir size with reference to the watershed size; the existence of other storages upstream in the basin; reservoir operation technique influencing detention time; as well as outlets provided and their location and size; and so on (CWC 2001; Mohanakrishan 2001). Added to this list of factors is the new and growing certainty that climate is changing and global warming the likely outcome (Bates et al. 2008), and that climate change will undoubtedly have an impact on sediment yield. Appendix 4A shows that the maximum rates of sedimentation are 38,253, 19,620, 19,439, 16,772, 12,707, and 11,060 m3/km2 yr–1 for Pothimund, Parson’s Valley in Tamil Nadu, Sarda Sagar in Uttrakhand, Kuttiyadi in Kerala, Chopadvav in Gujarat, and Mukurthy in Tamil Nadu, respectively; and the minimum rates of sedimentation are 7, 15, 18, 20, and 29 m3/km2 yr–1 for Pambar in Tamil Nadu, Palair in Telengana, Anaikuttam in Tamil Nadu, Dindi in Telengana, and Vembakottai in Tamil Nadu, respectively. The variability depends on the factors mentioned earlier. The observed rates of erosion at some of the large dams in India vary from 300 t/ km2 yr–1 for the dam on the Machkund River to 2,000 t/km2 yr–1 for the dam on the Tungabhadra River. For smaller tanks the rates are sometimes even larger (Garde & Kothyari 1985).

163

164

5.1.1

Reservoir Sedimentation

seDiment yielD maP

The method developed by Syvitski and Milliman (2007) to estimate sediment yield accounts for geologic features, climate, anthropogenic influences, population density, level of development, and topography. The method facilitates consideration of future catchment changes due to human influences (Annandale 2016b). Estimates of sediment yield by using geomorphic approaches involve dividing a catchment into geomorphologically similar regions to estimate sediment yield. According to Annandale (2016b), such approaches demand the expertise of a specialized geomorphologist. The traditional concern of geomorphologists has been the origin and evolution of landforms, but a new paradigm emerged which, based upon identification of system dynamics, gives emphasis to the prediction of landform response to natural and human influences. For example, a specific engineering project site, such as a reservoir, is part of a large geomorphic or fluvial system, and the characteristics of that fluvial system have an impact on the reservoir sited on that fluvial system. Therefore, it is important to incorporate an understanding of fluvial morphology, fluvial similarity (Rosgen 1994), and sediment behavior when creating sediment yield maps. Incorporating the knowledge of geomorphology/geology, and engineering would help solve engineering and environmental problems (Schumm & Harvey 2008). Kondolf et al. (2014) delineated nine distinct geomorphic regions for the Lower Mekong River basin based on geomorphic characteristics, geologic history, and available sediment transport data to estimate sediment yield.

5.2

PRONENESS OF HILLY AREAS TO SOIL EROSION AND FASTER RATE OF RESERVOIR SEDIMENTATION

Observed siltation rates vary widely from region to region with a wide variation in measured rates within regions in India (Figure 4.2). The rate of sedimentation is the highest in the reservoirs within Region 7, the region that contains west flowing rivers beyond Tapi and South Indian rivers. The median value of the rate of sedimentation observed in this region is 2,075  m3/ km 2 yr –1. Observation of the second highest rate of sedimentation (1,582 m3/ km 2 yr –1) is in the Himalayan rivers (Region 1) because of soil erosion by water. The annual soil erosion rate values range from less than 5 M g/ha –1 yr –1 for dense forests, snow clad cold deserts, and the arid region of western Rajasthan to more than 80 M g/ha –1 yr –1 (36 t/acre) in the Shiwalik hills. The extent of water erosion is more severe in the northeastern Himalayan (NEH) region (22.72 percent of total geographical area [TGA]) than in the northwestern Himalayan (NWH) region (12.61 percent of TGA) (Table 2.7). Washed from these hill slopes, the sediment settles down in the calm waters of the reservoirs. Major causes of excessive sedimentation of these reservoirs are uncontrolled deforestation, forest fires, unscientific quarrying, agriculture in hilly areas, and other development activities, such as the construction of roads, buildings, and hydro-power projects, all of which accelerate soil erosion in these regions.

165

Sediment Yield

TABLE 5.1 Loss of Storage (Percent) in Reservoirs in Himalayan Regions Name of Reservoir Pong Umium Bhakra Pili Chamera-I Chamera-II Baira Baigul Dhora Icari Nanak Sagar Ramganga Sarda Sagar Tehri

Annual Loss of Capacity (Percent)

Annual Loss for Zone (Percent)

0.28 0.32 0.39 0.59 2.46 2.6 2.81 0.66 0.48 1.28 0.3 0.15 0.5 0.2

0.93

The overall average annual loss in storage (percent) for 14 different reservoirs in Region 1 is 0.93 (Table 5.1). Water as well as wind erosion affect Southern Peninsular India. The Eastern Ghats and Western Ghats along the northern and western boundaries border Tamil Nadu State in the southernmost tip of peninsular India, meeting at Nilgiri Hills. The state has more than 3,000 sq. km ha under reservoir waterspread area. Western Ghats is a long peninsular mountain range that extends over 1,500 km with dense forests running parallel to the west coast from the south of Tapti valley in Maharashtra to Kanyakumari in Tamil Nadu. Southwest monsoons profoundly nourish reservoirs of Tamil Nadu and Kerala in the Western Ghats and rain shadow region. The southwest monsoons bring heavier rainfall in the western coastal plains of Kerala and the Western Ghats, but the monsoon winds lose much of their moisture and give very little rainfall to the eastern slopes, located in the rain shadow region, when they cross the Western Ghats. Tamil Nadu state also receives about 48 percent of the annual rainfall from the northeast monsoons, filling the reservoirs on the eastern side of the state during the monsoon season (Palaniswamy et al. 2015). Water and soil loss are severe to extremely severe in most of the hilly regions of Western Ghats, Madhya Pradesh, and Chhattisgarh. The state-wide percentage of degraded area to TGA is 59.1 percent for Madhya Pradesh and Chhattisgarh, whereas the states of Andhra Pradesh, Goa, Karnataka, Kerala, and Tamil Nadu have 21 percent, 18 percent, 38 percent, 13 percent, and 16 percent of TGA, respectively, of moderate to severe soil loss as reported by Bhattacharyya et al. (2015). Table 5.2a,b presents the annual storage loss computed from reservoir sedimentation surveys conducted by the Water Resources Organization (WRO) of Tamil Nadu

166

Reservoir Sedimentation

TABLE 5.2a Loss of Storage (Percent) in Reservoirs/Tanks in Tamil Nadu and Western Ghats of Tamil Nadu and Kerala Name of the Reservoir/Tank

Annual Loss of Capacity (Percent)

Annual Loss in Percent for Zone

Coastal Plains Veeranam tank Willingdon reservoir Wallajah tank

0.47 0.41 0.47

0.45

Central Plateau Barur tank Kaveripakkam tank Manimuthar reservoir Lower Bhavani reservoir Pechiparai reservoir Perunchani reservoir Aliyar reservoir Thirumurthy reservoir Mettur reservoir Vaigai reservoir Sathanur reservoir Amaravathy reservoir Manjalar reservoir Krishnagiri reservoir Ponnaniar reservoir Upper reservoir

0.04 0.12 0.13 0.14 0.34 0.23 0.20 0.30 0.38 0.30 0.47 0.35 0.75 0.85 1.52 1.58

0.48

Western Ghat (Tamil Nadu) Upper Bhavani reservoir Berijam reservoir Emerald avalanche Porthimund reservoir Mukurthy reservoir Parson\s valley reservoir Pegumbahalla reservoir Pillur reservoir Kundah reservoir Glenmorgan (FB)

0.18 0.23 0.22 0.67 0.55 1.48 2.57 0.91 2.87 1.79

1.15

Western Ghat (Kerala) Mangalam Peruvannamuzhi Malampuzha Peechi

0.39 1.66 0.28 0.27

0.65

Source: Samra and Sikka 2001; Updated with CWC 2015.

167

Sediment Yield

TABLE 5.2b Loss of Storage (Percent) in Reservoirs/ Tanks in Tamil Nadu and Western Ghats of Tamil Nadu and Kerala Coastal Plains Central Plateau Western Ghats (Hills) (Tamil Nadu and Kerala)

0.45 percent 0.48 percent 1.15 percent 0.65 percent

as well as CWC (2015) for reservoirs and tanks located in the coastal plains, central plateau and Western Ghats (Hills). The overall average annual loss in storage is 1.15 percent and 0.65 percent for the Western Ghats for Tamil Nadu and Kerala, respectively, 0.48 percent for the central plateau, and 0.45 percent for the coastal plains. These percentages clearly illustrate the proneness of hilly areas to soil erosion and faster rate of reservoir sedimentation. Nine of these reservoirs are in and around Ooty hills, one in Kodaikanal, and four in the Western Ghats of Kerala (Samra and Sikka, 2001). The rates of sedimentation in reservoirs of Porthimund, Mukurthy, and Parson’s Valley are categorized as severe class and all three reservoirs are situated (Region-4b) in the Western Ghats portion of Tamil Nadu (Figure 5.1). Comparison with the few available details of surveys in other reservoirs in Kerala demonstrates that the siltation rate is at par with that of reservoirs in other catchments in the state (Table 5.3; Suresh Babu et al. 2000; CWC 2015).

168

Reservoir Sedimentation

FIGURE 5.1 Reservoirs in Western Ghats. (a) Proneness of Hilly Areas to Soil Erosion and Faster Rate of Reservoir Sedimentation, (b) Average Annual Rate of Sedimentation from 100 km2 Catchment Area Is Higher for Reservoirs with Small Catchment Areas. The average annual  rates of sedimentation from unit catchment areas for the Sarda Sagar (127 km2), Manikdoh (129 km2), Pykara (38 km2), Mukhurthi (25.25 km2), Persons Valley (14.5 km2), Porthimund (10.55 km2), Chopadav (27 km2), and Kuttiyadi (39 km2), are 194.39, 121.67, 100.91, 110.6, 196.2, 382.53, 127.07, and 167.72 ha.m/100 km2 yr–1, respectively due to factors such as small size of catchment areas, total relief, land use/land cover (LULC) changes, soil erosion, and rainfall characteristics.

169

Sediment Yield

TABLE 5.3 Comparison of Reservoirs Based on Sedimentation Rates

Reservoirs Mangalam Peruvannamuzhi Malampuzha Peechi Neyyar

Catchment (km2)

Live Storage Capacity (M m3)

Last Year of Survey

Period of Records (years)

Annual Storage Loss (Percent)

48.85 108.8 147.63 107.00 140.00

24.67 113.45 226.96 109.00 101.15

2008 1986 2006 2004 2011

52 13 39 47 47

0.39 1.66 0.28 0.27 0.16

Data Source: Suresh Babu et al., 2000; CWC, 2015.

5.3

RELATIONSHIP OF LAND USE AND LAND COVER CHANGE TO RESERVOIR SEDIMENTATION

The relationship of land use and land cover to reservoir sedimentation is apparent in different parts of the world. The land use pattern within a drainage area can contribute to the high sedimentation rate in the early life of a reservoir. In India, the areas most prone to the negative environmental effects of the Green Revolution were semiarid or temperate environments where the agricultural changes were most aggressively implemented. The area of eastern Gujarat is one of these environments. The region is characterized by a pronounced dry season from November through April with periodic droughts every 3–4 years. It is home to some of the largest irrigation projects in the country and the impact of agricultural intensification is pronounced. The Karjan, Meshwo, Mukteshwar, and Sipu reservoirs in Gujarat with sediment yields of 2,241, 3,861, 1,835, and 8,950 m3/km2 yr–1, respectively, are worth mentioning here. The El30 (annual erosion index in metric unit) values for west flowing rivers below the Tapi and for the DVC river basins are higher than 1,000 as mentioned by Narayana and Ram (1983). The Damodar River, a subsystem of the Ganga, rises in the Chhotanagpur (plateau) watershed at 23°37′ N and 84°41′ E. The entire drainage basin resembles a tadpole. In its upper sector, the Damodar flows through quartz-rich Archean gneiss. In its middle stretch lies the Raniganj coalfield, that is, the Damodar flows through the sandstone-rich Gondwana sedimentaries. The main tributaries are the Barakar, Tilaiya, and Konar. Below the confluence of the Barakar there are a few insignificant tributaries. As the Damodar catchment is generally denuded of forest cover, soil erosion first takes place in the form of sheet and gully erosion and the stream carries a large amount of coarse and fine-grained sediment during monsoon months. The general picture of the upper Damodar watershed is that it abounds in long stretches of generally sloping well terraced uplands where paddy fields can be cultivated. Unterraced wasteland and uplands are exposed to serious sheet erosion. A lot of destructive gully systems are also prevalent wherever the ground advances a mainstream bed. Vast stretches of rolling forested terrain are also subjected to serious sheet and gully erosion (DVC 1997; Bhattacharyya 2000, 2011).

170

Reservoir Sedimentation

In the study of the Damodar River, Bhattacharyya (1998, 2000, 2011) observed that due to extensive deforestation and unscientific mining, the Damodar River used to carry an enormous sand load during flood days in the past and formed several char lands (sandbars) in the river. This began particularly after 1830 when several collieries in the Raniganj coalfield were prosperous. Denuding of forest and vegetal cover, inappropriate land management, and badly eroded land predominant in the catchment areas of Maithon, Panchet, and Konar (CWC 1999) are responsible for the high sediment yield in these reservoirs. Among these, the sedimentation rate in Tilaiya is about 2,792 m3/km2 yr –1 (Appendix 4A). The sedimentation rate at the Panchet reservoir has decreased after the construction of the upstream reservoir at Tenughat. A strong linkage between changing geomorphic space and perceived environment is also observed and influenced by humans. Changes in real environment are recorded on the geographical space. Different types of control structures, including dams, reservoirs, barrages, changing boundaries of sandbars, opening of spill channels, deterioration of distributaries, and other similar changes leave their recognizable imprints on the surface (Bhattacharyya 1997, 1998, 2011). Perceived environment is reflected in land use practices as shown in the following through the examples of Gangtikali (Figure 5.2) and Sitarampur Mana, Ramkrishna Palli, and Pallishri Squatters’ colony, situated below the Maithon and Panchet reservoirs and below the Durgapur barrage, respectively (Figure 5.3). In Gangtikali, there was a change in real environment when coal mines on the west were flooded in 1959. Prior to this event, the riparian communities did not perceive the agricultural resource potential of the east side. In fact, the coal mining company dictated their interaction with the environment which saw Gangtikali only as a geological resource. After the 1959 floods, however, the riparian communities, driven by the need to look beyond coal mining, began to realize the agricultural resource potential of the eastern part of the sandbar (Bhattacharyya 1998, 2000, 2011). In sandbars below the Durgapur barrage, land use bears the imprint of a functional relationship between the riverbed and its occupiers. As a result, the forms, processes, and materials in the riverbed are no longer fundamental entities but deserve functional identity. This does not necessarily mean that riverbed characteristics of the controlled sector totally govern the land use characteristics. People’s culture, perceptual capability to evaluate an environment, and their position in society also play a critical role in decisionmaking regarding specific land use (Plate 5.1). A cultural landscape developed in the Damodar catchment has resulted from human intervention with the physical landscape through specific culture, and, ultimately, components of the inherited physical landscape become inseparable from the superposed components of cultural landscape. Plate 5.1 shows flood zoning in the river bed. The occupiers have extended their resource base horizontally by using all available land, and vertically as well through multiple cropping. They have accepted the flood risk and looking at the bright side of the floods, they have learnt to underestimate the danger of living in a flood-prone micro environment, therefore, the flood reduction measures especially non-structural measures adopted by the riparian communities often pose a challenge to the technology and capital-intensive measures adopted by the governments (Basu & Bhattacharyya 1991; Bhattacharyya 1998, 2011). The riparian landscape of the Damodar River is continuously transforming into a hybrid landscape. The Durgapur Barrage on the Damodar River has lost more than 45 percent of its storage capacity in less than 56 years of operation due to accumulated sediment.

171

Sediment Yield

100

1957 References Agricultural land Settlement Scrub and grass B ar

Submersible sand River channel

aka

86°48′30″E

rR

100

.

Contour in m. Coal mine

23°41′30″N

110 120 100

(Disused) 100

DA M

OD AR

100

R. 100

m 500

0

500

2000

1000 m

FIGURE 5.2 Changing Cultural Landscape of Gangtikali Situated below Lower Reservoirs: Maithon and Panchet. In Gangtikali, there has been a shift of resource base from geological to agricultural with a consequent change in settlement site. At present all available space on the sandbar is being used objectively and rationally. As human perception and the appraisal of environment have changed, the concept of resource evaluation has widened (Source: Bhattacharyya, 1997, 1998, 2011).

FIGURE 5.3 Changes in Generalized Land Use Characteristics and Landscape: below Durgapur Barrage. The Damodar River landscape is gradually changing from natural to hybrid after being legally occupied mostly by riparian communities. Once a group of mobile sandbars, it is now a static landform in a controlled riverbed due to continuous interactions between geomorphology and riparian society. (Source: Bhattacharyya, 2011, 2016.)

172 Reservoir Sedimentation

Sediment Yield

173

PLATE 5.1 Generalized Model Showing Relationship between Physical and Cultural Landscape (Source: After Bhattacharyya, K. 1998, 2011.) The land use characteristics in the Damodar River have become viable parameters for assessing microforms, processes, and materials and the interrelationship between physical and selected components of the cultural landscape. i. When the first group of settlers arrived in the riverine bars, the Durgapur Barrage,  and the Maithon and Panchet reservoirs were yet to be constructed. There was a rapid change in the natural environment when these three emerged as major transverse control structures. ii. Monsoon flow decreased, peak flow reduced, and there was a shift of peak flow from July–August to September. There is little doubt that the change in the environment due to riparian communities was just as rapid. The communities quickly discerned the effect of water release from the reservoirs and barrage and the inundation patterns of their land. iii. Riparian communities can estimate how much area will be inundated if the release of water below the Durgapur Barrage exceeds 4,531 m3/s or 5,664 m3/s. iv. In the decaying channel beds D1 clay deposited from vertical accretion is used for double cropping and the crop selected is clay loving rice. The erosion prone peripheral area is used as grassland or for additional crops. Settlements are strikingly linear along the main road and located on higher grounds. Multiple crops are found on the higher parts of the bars with irrigation facilities. An open space with a school ground located on the highest part of the sandbar is used as a flood shelter. Sandbars or char lands in the Damodar River are epitomes of riverbed utilization. Every possible element of available land is put to some use so as to optimize benefits from microrelief variations, edaphic differences, and water level fluctuations (Basu & Bhattacharyya 1991; Bhattacharyya, K. 1997, 1998, 1999, 2011).

174

Reservoir Sedimentation

The above mentioned examples illustrate that wherever the catchment area is largely under cultivation of annual crops, faulty land management activities, estates, and human activities and interferences, the reservoir sedimentation rate is higher (Samra & Sikka 2001). The Nilgiri district is also a good example of human activities and interferences and the higher rate of reservoir sedimentation. There are fifteen hydropower reservoirs in the Nilgiri district. Table 5.4 presents details of ten reservoirs in the Nilgiris in terms of their storage, loss in capacity, and land use in their respective catchments. The table clearly shows that the Kundah and Pillur are the worst affected reservoirs with a percentage annual loss of capacity of 2.87 percent for Kundah and 0.91 percent for Pillur. Black soils or vertisols and the associated soil region of India, occupying a 73 M ha area in Karnataka, Andhra Pradesh, Telengana, Madhya Pradesh, and Maharashtra, are usually utilized for crop production under rain-fed conditions. Although black soils have a relatively high moisture holding capacity, not all water is available to plants because the smectitic clay holds the water tenaciously. The smectitic clay has a high coefficient of expansion and contraction, leading to the development of gilgai microrelief, deep and wide cracks, and closely intersecting slickensides. Due to poor workability of this type of soil, farmers get a narrow window of time for crop sowing. As a result, some vertisols remain fallow even during the rainy season (Bhattacharyya et al. 2015). Keeping these lands uncultivated during the intense rainy season renders them susceptible to serious erosion (Narayana & Babu 1983). Erosion rates in the black soil region are 20 M g/ha–1 yr –1. Red soils of the Chhotnagpur plateau also recorded a soil loss value of 10 to 15 M g/ha–1 yr –1 (Singh et al. 1992). Reservoirs situated in the black soil region have high sedimentation rates. For example, the Nizamsagar Reservoir situated in the black soil region of Telengana has lost 60.47 percent of its capacity just within 62 years of its existence (Appendix 4D). Samra and Sikka (2001) reported high rates of siltation in various hydropower reservoirs in and around the Nilgiris. Spatial patterns in sediment yield here are a consequence of human interference. Human impact is stronger in yielding high sediment in reservoirs, such as Parsons Valley, Mukurthy (Region 4b), Kundah, and Pillur (Region 4a) in Tamil Nadu. Using data from 61 gauging stations in Southern Kenya, Dunne (1976) demonstrated that land use is a dominant factor explaining the variability in sediment yield. Data on sediment yield for selected physiographical regions in the United States illustrates both the variation between regions as well as the wide variation of measured rates within regions. Within a single watershed, only a small fraction of the landscape is usually responsible for a large percentage of sediment yield. The effect of land use and land cover on erosion and consequent sedimentation is difficult to estimate, as other local conditions may dominate (Morris & Fan 1998). Research has shown a significant increase in sediment yield due to land use change following deforestation. These changes can have dramatically different effects on sediment yield, depending on the type of change and the antecedent watershed conditions (Mixon 2002). For example, land-use changes documented along the Yangtze in China show an increase in erosion by a factor of 3–4, while deforestation in Illinois resulted in erosion rates 30-100 times the previously measured value (Einsele & Hinderer 1995; Mixon 2002). In other situations, the reservoir itself can become an instance of land use change as the energy, water, and recreational opportunities provided by it increase local population

Upper Bhavani

1967

1966 1966 1938 1976 1953

Pillur

Parsons Valley Porthmund Mukurthy Glenmorgan (FB) Lower Bhavani

19.25 60 50.98 5.85 932.78

44.40

1.07

156.75 1.76

101

Original Capacity (M m3)

1995 1996 2006 1998 1983

2013

1982

2000 1982

1985

Year of Last Survey

Source: Samra and Sikka, 2001; CWC, 2015.

1966

Pegumbahalla

Emerald Avalanchi 1961 Kundah 1960

Year

1965

Name of Reservoir

11 47.89 31.99 3.55 895.03

25.91

0.63

149.574 0.65

97.48

8.25 12.11 18.99 2.30 37.75

18.49

0.44

7.176 1.11

3.72

42.86 20.18 37.25 39.32 4.05

41.64

41.12

4.58 63.07

3.68

Capacity as Capacity Per Last Capacity Loss Survey Loss (M m3) (Percent)

TABLE 5.4 Land Use and Reservoirs Sedimentation in and around Nilgiri Hills

1.48 0.67 0.55 1.79 −0.14

0.91

2.57

0.22 2.87

0.18

Percent of Annual Siltation Remark

Catchment with vegetation and forest plantation and no human disturbances Not much disturbance in the catchment Catchment area subjected to annual cultivation and lot of human activities Catchment area subjected to annual cultivation and a lot of human activities Catchment partially under forest and subjected to faulty agricultural activities, but measures taken and percent annual loss has been decreased from 2.43 to 0.91 Catchment partially under forest and human activities Catchment under forest and not much disturbance Rate of siltation increased due to a lot of human activities Catchment area, mostly estates and agricultural activities Catchment area, mostly forest land and sediment deposited in upstream reservoirs

Sediment Yield 175

176

Reservoir Sedimentation

and influence subsequent land use (Zhou & Xiaoqing 1997; Mixon 2002). Zhao et al. (2010) observed that dam construction has caused pressure on changes in land use and forest land in the Manwan reservoir in Yunnan, China, which has deteriorated with time. White (2001) referred to the example of the Ringlet reservoir in Malaysia which showed the dramatic effects of deforestation. The catchment area changed gradually from forest to plantations and holiday facilities. As a result, the rate of sedimentation is now eight times higher than it was in the mid-1940s. Construction sites showed an even greater increase in sediment yield when compared with agricultural areas (Mixon 2002). Wolman (1989) documented data that reveals a significant difference in sediment yield among basins with forested catchments (20 percent wasteland (NRSA 2000).

Watershed approach Participatory resource conservation and management Construction of upstream dams

Sediment bypass

Flood bypass by tunnel/ channel

Offchannel reservoir

Sediment passthrough Turbidity current venting

Sluicing (partial or complete drawdown)

Recover, increase or reallocate reservoir volume Mechanical excavation Manual excavation Hydraulic dredging

Hydraulic power Complete drawdown flushing

(Continuous) sediment transfer

Pressure flushing

Redistribute sediments (inside reservoir)

Hydrosuction (HSPS, siphoning)

No action Run-of-river HPP

Sedimentation strategies

Soil erosion control

Routing sediments around or through reservoir

Dam removal

Reduce sediment yield from upstream watershed

Enlarge storage (Dam heightening)

FIGURE 6.1 Classification of Strategies against Reservoir Sedimentation. (Source: After Auel et al., 2016.)

Reservoir Sediment Management Strategies

197

(a)

(b)

(c)

PLATE 6.1 (a) Eroded Reservoir Bed of Maithon during the Non-monsoon Period. (b) Maithon Reservoir during the Non-monsoon period. (Source of Photographs: D. Chaudhuri, DVC engineer, Kolkata, India.) (c) Maithon Reservoir during the Monsoon Period. (Source of Photographs: India: WRIS.)

Countries have also placed a great deal of emphasis on sediment management through the control of erosion but this alone cannot establish a sediment balance across the impounded reach while maximizing long-term capacity. An integrated approach to sediment management involves employing all feasible strategies that countries can use to balance the sediment budget across reservoirs, while minimizing trap efficiency and maximizing long-term storage capacity. Countries usually adopt combinations of different measures to gain the maximum effect (Morris 1995a; Liu et al. 2002).

198

Reservoir Sedimentation

(a)

(b)

(c)

(d)

PLATE 6.2 (a) Sediment Flushing at Three Gorges Dam with Millions of Tons of Silt Flushed. (Source of Photographs: https://www.theguardian.com/environment/gallery/2010/jul/21/ three-gorges-dam.) (b) Emptying Three Gorges Reservoir to Flush the Sediment Out. (c) Sediment Flushing at Sanmenxia Dam (Phase-I). (d) Sediment Flushing at Sanmenxia Dam (Phase-II). (Source of Photographs: Shi Qi, Personal communication through emails.)

199

Reservoir Sediment Management Strategies

Reservoir benefits may be sustainable if a reservoir provides a storage volume that exceeds the volume of expected sediment supply in the turbidity watershed. The sediment storage volume may be included within the reservoir pool or in one or more upstream impoundments. The deposition of sediment may be in areas where its subsequent removal is accelerated or where it minimizes intervention with reservoir operations (Rao et al. 2014).

6.1.1

reDuce seDiment yielD from uPstream WatersheD

The first strategy in this chapter refers to a decrease in the inflow of sediment to the reservoir by adopting catchment erosion control techniques, that is, following watershed approach and implementing participatory resource conservation and management, constructing upstream dams, and check or sabo dams. 6.1.1.1 Soil Erosion Control Soil erosion, a complex dynamic process, creates exposed subsurface where the soil is detached and deposited in low-lying areas of the landscape, a process known as sedimentation. Soil erosion and sedimentation are concurring environmental processes with diverse negative and positive impacts (Nallanathel & Santhanam 2014). The projection of economic damages associated with soil erosion in North America is in excess of US$16 billion per year (Osterkamp et al. 1998). Countries expend a great deal of effort to control and decrease soil erosion rates through watershed management techniques (Palmieri et al. 2003). Appendix 6A gives the salient mitigation techniques for reversing land degradation in India and their applicability in major agro-climate zones. Mandal and Sharda (2011) employed a quantitative biophysical model for the assessment of soil loss tolerance limits (SLTLs) (permissible soil loss) in India. The concept of SLTLs evolved to prevent land degradation that can impact the livelihood of people rendered landless due to its adverse effects. Assessment of soil loss tolerance (T-value) safeguards long-term sustainability of the soil resource by preventing excessive erosion through suitable conservation measures. Table 6.1 presents an overall picture of the performance of soils, with respect to erosion resistance and

TABLE 6.1 Area under Different SLTLs of India SLTL (M g ha yr –1) 2.5 5.0 7.5 10.0 12.5 Non-soil Total geographical area Source: Mandal and Sharda, 2011.

Area (M ha) 24.24 16.09 61.98 85.86 105.41 35.15 328.73

Total Geographical Area (Percent) 7.37 4.90 18.85 26.12 32.07 10.69 100

200

Reservoir Sedimentation

tolerance, for all physiographical regions of India. Analyses calculated the T-values based on the soil group versus depth matrix. The T-values in each physiographical region ranged from 2.5 to 12.5 M g/ha–1yr –1 , representing wide deviation in soil ability to resist the impact of water erosion on crop productivity. About 57 percent of the area in India has a permissible soil loss of less than 10.0 M g/ha–1yr –1. India needs to preserve this level with suitable conservation measures (Mandal & Sharda 2011). Tables 6.2 and 6.3 give the T-values of hilly regions of India as estimated by Mandal et al. (2010). The projection is that ~59 percent of land within the hilly region requires some form of erosion management to achieve the desired T-value (Mandal et al. 2010). TABLE 6.2 Area under Different Erosion Rates and Soil Loss Tolerance Limits in the Northwestern Hills Erosion Categories Based on Soil

Very Severe (>40)

Other

1.9 (5.8)

4.5 (13.7)

19.2 (58.0)

7.5

10.0

12.5

3.5 (10.6)

9.0 (27.2)

1.3 (3.9)

Rocks/ unreported 18.7 (56.3)

Very Low (