Coastal Fishery Projects: construction, maintenance and development 9781315139647, 1315139642, 9781351459983, 1351459988

Table of contents :
Content: Cover
Half Title
Title Page
Copyright Page
ON THE PUBLICATION OF THE REVISED EDITION
CHAIRMAN'S NOTE
EDITOR'S NOTE
Table of Contents
PART 1: GENERAL RULES
CHAPTER 1: GENERAL RULES
1.1. Objective of the Manual
1.2. Relationship with the Local Environment
1.3 Framework Prescribed in the Manual
1.4 Relationship with Other Development Projects in the Region
PART 2: DESIGN CONDITIONS
CHAPTER 1: DESIGN WATER LEVEL
1.1. General
1.2. Calculation of Tide Levels
CHAPTER 2: WAVES
2.1. Computing Deep Water Waves
2.1.1. General
2.1.2. Basic characteristics of waves 2.1.3. Method of determining various characteristics of the deep-water wave in the design2.1.4. Determination of the various characteristics of the design deep-water wave
2.1.5. Computing unrefracted deep-water wave height
2.2. Computation of Design Wave
2.2.1. General
2.2.2. Computation of a wave from its generating area
2.2.3. Calculation of characteristics of swell
2.3. Transformation of the Wave
2.3.1. General
2.3.2. Shallow water transformation
2.3.3. Refraction of waves
2.3.4. Diffraction of waves
2.3.5. Reflection of waves
2.3.6. Breaking wave height
2.4. Wave Force 2.4.1 General2.4.2. Effect of wave pressure on a vertical wall
2.4.3. Stability of rubble structures or rubble breakwaters
CHAPTER 3: COASTAL CURRENTS
3.1. General
3.2. Design Current Velocity
CHAPTER 4: LITTORAL DRIFT
4.1. Characteristics of Littoral Drift
4.1.1. General
4.1.2. Types of littoral drift
4.2. Quantum of Littoral Drift
4.2.1. Water depth limits for littoral drift and changes in the longshore bar
4.2.2. Prevailing direction of littoral drift
4.2.3. Quantum of littoral drift
4.3. Sand Movement
CHAPTER 5: SOIL CONDITIONS
5.1. General
5.2. Sub-soil Investigations 5.3. Physical Characteristics of the Soil5.3.1. General
5.3.2. Important physical characteristics of soil
5.3.3. Classification of soils
5.4. Mechanical Properties of Soil
5.4.1. General
5.4.2. Shear strength of soil
5.4.3 Cohesive strength of clayey soil
5.5. Soil Pressure
5.5.1. General
5.5.2. Soil pressure of sandy soil
5.5.3. Pressure due to clayey soil
5.6. Residual Water Pressure
PART 3: GENERAL INFORMATION
CHAPTER 1: GENERAL INFORMATION
1.1. Objective
1.2. Weight (Per Unit Volume) of Material
CHAPTER 2: CONCRETE
2.1. Quality of Concrete
2.2. Cover
2.3. Stirrups 2.4. Permissible Intensity of Stress2.5. Conditions for Design Mix
CHAPTER 3: STEEL
3.1. Quality of Steel
3.2. Steel Constants Used in Design Conditions
3.3. Permissible Stresses
3.4. Rate of Corrosion
3.5. Joints
CHAPTER 4: OTHER MATERIALS
4.1. Quality of Material
PART 4: DISCUSSION ON DIFFERENT COMPONENTS
CHAPTER 1: FISH CAGES FOR CULTURE
1.1. General
1.2. Design of Structures
1.3. Design External Load
1.4. Impact at Time of Submersion
1.5. Hydrodynamic Force
1.6. Strength of Members
1.7. Stability of Fish Cages
1.8. Floating Fish Cage
1.8.1. Objective and structure

Citation preview

Coastal Fishery Projects

Coastal Fishery Projects Construction, Maintenance and Development

All-Japan Association for the Development and Promotion of Coastal Industries Tokyo

Translated from the Japanese

CRC Press Taylor & Francis Group Boca Raton London New York CRC Press is an imprint of the Taylor & Francis Group, an informa business

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ON THE PUBLICATION OF THE REVISED EDITION

The “ Plan for the Development and Construction of Coastal Fishing Areas” was originally published with a view to providing construction designs for developing coastal fishing areas. The manual laid down standard methods for construction designs; however, with the advances in technology during the next several years, as well as other factors, revising this plan became necessary. Up to now, the “ Plan,” presented in 1974 by the Japanese Association for the Protection of Marine Resources contained the “ First Plan (1976)” for a proper development of coastal fishing areas and was accompanied by the enactment of the law for the development of coastal fishing areas in 1978. The present work arose because the “ Second Plan (1982)” for the development of coastal fishing areas became necessary following a noticeable increase in the scale of the industry as well as in the knowledge pertaining to maritime engineering. It thus became necessary to revise the existing work and, in October 1983, the Association established an editorial committee and began investigating the process of revision. This work was completed during the specified plan period. The internal and external environment of our fishing industry is truly very difficult and it is becoming increasingly important to properly develop the cultivation and propagation of marine resources as well as to plan for an increase in the production of the fishing industry. The revised plan will provide important data for the regional development of coastal fishing areas, and we hope it will help the rationalization and productivity of the industry. We gratefully acknowledge the assistance provided by the faculty of the Association and the Editorial Committee during the publication of the revised “ Plan.” Chairman Director Kyichi Miahara All-Japan Association for the Development and Promotion of Coastal Industries

CHAIRMAN’S NOTE

The environment for our country’s fishing industry has become very difficult in view of the increased costs of materials used in the fishing industry, particularly the rise in oil price and a drop in the demand for marine products as well as the adoption of the 200-mile limit for coastal zones by many countries which has put restrictions on the area of operations. However, as we derive over half of our animal proteins from fish, we must use our rich resources more effectively to meet a situation, in which it has become necessary, and urgent, to vigorously promote the coastal fishing industry with the 4‘cultivated fishing industry” as the central theme. In the coastal fishing industry, because of these reasons, the ‘‘cultivation of sea-fields” has become very important and the proper development of the coastal fishing industry must be planned accordingly. The proper development of coastal fishing areas has now been going on for six years, from 1982 to 1987 and in this period the total project cost has been estimated at 40 billion yen. The Second Plan for the Proper Development of Coastal Fishing Areas was based on this project. The establishment of fishing cages, building of fish culturing areas and the protection of coastal fishing areas in this industry are being implemented entirely in accordance with the plan, but it is necessary for further improvement to use maritime engineering technology which is an independent technical field. The Plan for Construction, Maintenance and Development of Coastal Fishing Areas was started in 1978 and experts from many disciplines have participated in the realization of this plan. However, because of the remarkable increase in technical knowledge regarding maritime engineering and the increase in the scale of the projects, it was desirable that the plan be revised. The plan was revised and enlarged, and in this form is being published by the All-Japan Association for the Development and Promotion of Coastal Industries. The present work has effectively and rationally presented the material on coastal fishing area facilities and their construction designs and it is hoped

that this will lead to an appropriate progress in the maintenance and construction of coastal fishing areas. It is also hoped that this work will find wide application. Hiroshi Suno Chairman Promotion Division Maritime Department

EDITOR’S NOTE

It has been six years since the 1978 edition of the Plan for the Maintenance, Development and Construction of Coastal Fishing Areas was published. The book has, during this period, come to be known as the “ Orange Book’’ because of the color of the cover, and the views expressed in the plan have since come to be accepted. It became necessary to publish a revised edition with the development of new technologies and improvement of construction facilities. Moreover, using this opportunity, the contents were amplified and the section on the existing standards of certain constructions on the coast, particularly the design standard of fishing ports, was deleted as these are now readily available. This is a completely revised plan. The major revisions of the plan are the following. In Part 2, Design Conditions, the direction spectrum of the wave is considered. The rules for a new method for deriving the design current speed are given. There is a slight numerical increase for drift sand. There are newly established ideas about soil quality for heavy construction, such as breakwaters. Part 3, General Information, has been revised and the contents improved. In Part 4, Discussion on Different Components, the range of coefficient of base counterforce has been reduced to 300 -500 kg/cm2. Rules have been established for the design of steel fishing cages. The items important for floating fishing cages have been discussed. For the maintenance of sea-water quality, the method of selecting construction materials, sea-water exchange because of internal splashing, sea-water exchange because of tides, etc., have been examined. Further, the formula for the stability of piled rocks has been revised on the basis of on-site experiments. The construction method for preventing the blockage of the river entrance has been added to the river entrance environment. Here, the environment conditions for marine products and the values of the environment characteristics, according to fish species, have been given in the Appendix. Aside from these changes, there are only minor alterations and the earlier plan has been largely followed. Coastal construction differs from the existing marine engineering construction as it includes the ocean area and there are many areas which need

to be independently developed. Many problems were recognized, but they could not be standardized. It is hoped that further research reports and experimental observations will be presented at appropriate meetings and conferences. It is hoped that the present plan is efficacious, and assists in a steady progress in maintenance and development of coastal fishing areas. Editorial Committee of the Plan for the Construction, Maintenance and Development of Coastal Fishing Areas

MEMBERS OF THE EDITORIAL COMMITTEE FOR DESIGN OF CONSTRUCTION FOR DEVELOPMENT OF COASTAL FISHERY PROJECTS

Chairman Kazumitsu Kawada

Development Section, Maritime Department

Deputy Chairman Noboru Nakamura

Planning Section, Maritime Engineering Research Center

Head, Central Division Nobuo Takaako

Development Section, Maritime Department

Head, Environment Division Toshifumio Numa

Fishery Area Hydrography Research Center, Maritime Engineering Research Center

Head, Facilities Division Masao Kamikita

Fishery Area Facilities Research Center, Maritime Engineering Research Center

Members Kyichi Kawaguchi Yuji Nishi Kunikazu Asaoka Kazuo Higo Yuzaburo Miyazaki

Center for Development, Department Center for Development, Department Center for Development, Department Center for Development, Department Center for Development, Department

Maritime Maritime Maritime Maritime Maritime

xii Iida Minoru Akio Saito

Promotion Division, Development Center, Maritime Department Department of Planning, Extension Division

MEMBERS OF THE COMMITTEE FOR DESIGN OF COASTAL DEVELOPMENT WORKS

Chairman Yasuo Oshima

Professor Emeritus, Tokyo University

Members Hiroo Inoue Hiroshi Iida Torn Jinki Hiroyasu Shimura Teruo Sugawara Yoshio Tohara Noboru Nakamura Toshiyuki Hirano Reijiro Hirano Akinobu Hiwata Tateo Shima

Professor, Department of Agriculture, Kagawa University Chairman, Maritime Research Center, Hokkaido Prefecture Professor, Engineering Department, Osaka University Professor, Department of Agriculture, Tokyo University Head of Maritime Engineering Division, Maritime Engineering Research Center Professor, Department of Agriculture, Saga University Head of Planning Section, Maritime Engineering Research Center Professor, Ocean Research Center, Tokyo University Professor, Department of Agriculture, Tokyo University Fishery Ports Division, Department of Construction, Fishery Ports Division Fishery Ports Division, Department of Protecting Fishery Areas, Research Division, Maritime Department

xiv Teruo Tsunawara Shizuya Hagino Yoshinobu Yasunaga Masaki Omaki Sadamitsu Akeda Tetsu Morita

Ryukan Yamane

Division of Maritime Engineering, Maritime Engineering Research Center System Development Research Center, Maritime Engineering Research Center Environmental Analysis Research Center, Maritime Engineering Research Center Fishery Port Facilities Research Center, Maritime Engineering Research Center Fishery Area Research Center, Maritime Engineering Research Center Environmental Control Research Center, Environmental Management Division, Cultivation Research Center All-Japan Association for the Development and Promotion of Coastal Industries

CONTENTS

PART 1. GENERAL RULES CHAPTER 1. GENERAL RULES ... 1.1. Objective of the Manual ... 1.2. Relationship with the Local Environment ... 1.3 Framework Prescribed in the Manual ... 1.4 Relationship with Other Development Projects in the Region ...

3 3 3 4 5

PART 2. DESIGN CONDITIONS CHAPTER 1. DESIGN WATER LEVEL 1.1. General 1.2. Calculation of Tide Levels

... ... ...

9 9 10

CHAPTER 2. WAVES 2.1. Computing Deep Water Waves 2.1.1. General 2.1.2. Basic characteristics of waves 2.1.3. Method of determining various characteristics of the deep-water wave in the design 2.1.4. Determination of the various characteristics of the design deep-water wave 2.1.5. Computing unrefracted deep-water wave height 2.2. Computation of Design Wave 2.2.1. General 2.2.2. Computation of a wave from its generating area 2.2.3. Calculation of characteristics of swell 2.3. Transformation of the Wave

... ... ... ...

13 13 13 16

...

19

... ... ... ... ... ... ...

23 25 26 26 31 34 38

/

xvi 2.3.1. General 2.3.2. Shallow water transformation 2.3.3. Refraction of waves 2.3.4. Diffraction of waves 2.3.5. Reflection of waves 2.3.6. Breaking wave height 2.4. Wave Force 2.4.1 General 2.4.2. Effect of wave pressure on a vertical wall 2.4.3. Stability of rubble structures or rubble breakwaters CHAPTER 3. COASTAL CURRENTS 3.1. General 3.2. Design Current Velocity

... ... ... ... ... ... ... ... ... ...

38 39 42 47 65 66 70 70 71 79

... ... ...

82 82 88

CHAPTER 4. LITTORAL DRIFT 4.1. Characteristics of Littoral Drift 4.1.1. General 4.1.2. Types of littoral drift 4.2. Quantum of Littoral Drift 4.2.1. Water depth limits for littoral drift and changes in the longshore bar 4.2.2. Prevailing direction of littoral drift 4.2.3. Quantum of littoral drift 4.3. Sand Movement

... ... ... ... ...

91 91 91 94 97

... ... . . . . . .

97 99 100 103

CHAPTER 5. SOIL CONDITIONS 5.1. General 5.2. Sub-soil Investigations 5.3. Physical Characteristics of theSoil 5.3.1. General 5.3.2. Important physical characteristics of soil 5.3.3. Classification of soils 5.4. Mechanical Properties of Soil 5.4.1. General 5.4.2. Shear strength of soil 5.4.3 Cohesive strength of clayey soil 5.5. Soil Pressure 5.5.1. General 5.5.2. Soil pressure of sandy soil 5.5.3. Pressure due to clayey soil

... . . . . . . ... ... ... ... ... ... ... . . . . . . . . . . . . ...

105 105 106 110 110 110 112 115 115 120 124 129 129 129 131

xvii 5.6.

Residual Water Pressure

. . .

132

CHAPTER 1. GENERAL INFORMATION 1.1. Objective 1.2. Weight (Per Unit Volume) of Material

... . . . ...

137 137 137

CHAPTER 2. CONCRETE 2.1. Quality of Concrete 2.2. Cover 2.3. Stirrups 2.4. Permissible Intensityof Stress 2.5. Conditions for Design Mix

... . . . . . . . . . . . . . . .

138 138 140 140 141 141

CHAPTER 3. STEEL 3.1. Quality of Steel 3.2. Steel Constants Usedin Design Conditions 3.3. Permissible Stresses 3.4. Rate of Corrosion 3.5. Joints

... . . . . . . . . . . . . . . .

144 144 144 145 145 146

CHAPTER 4. OTHER MATERIALS 4.1. Quality of Material

... ...

147 147

PART 3. GENERAL INFORMATION

PART 4. DISCUSSION ON DIFFERENT COMPONENTS CHAPTER 1. FISH CAGES FOR CULTURE 1.1. General 1.2. Design of Structures 1.3. Design External Load 1.4. Impact at Time of Submersion 1.5. Hydrodynamic Force 1.6. Strength of Members 1.7. Stability of Fish Cages 1.8. Floating Fish Cage 1.8.1. Objective and structure 1.8.2. Design external force 1.8.3. Anchor rope tension 1.8.4. Anchor

... . . . ... ... .. . . . . ... . . . ... . . . . . . . . . ...

153 153 153 154 155 158 162 164 170 170 173 175 176

xviii CHAPTER 2. SELECTION OF TYPE OF WORKS TO IMPROVE AND MAINTAIN WATER QUALITY IN HATCHERIES 2.1. Objective CHAPTER 3. IMPROVEMENT OF BAY ENTRANCE OF LAGOONS 3.1. Objective 3.2. Optimum Parameters 3.3. Main Features of the Plan 3.3.1. Hydrographic characteristics of bay entrance 3.3.2. Sea water exchange caused by tides 3.3.3. Sea water exchange caused by hydraulic flux/wave breaking within bay 3.3.4. Sea water exchange caused by density currents 3.4. Optimum Bay Entrance Structure 3.5. Selecting Construction Method

... . . .

178 178

... .. . ... .. . . . . ...

183 183 183 185 185 186

.. . . .. ..

189 193 193 194

. . . .

CHAPTER 4. USE OF TIDAL CURRENTS FOR SEA WATER EXCHANGE IN A HATCHERY 4.1. Objective 4.2. Optimum Parameters 4.3. Sea Water Exchange Flows 4.4. Sea Water Exchange

. . . 199 . . . 199 . . . 199 . . . 200 . . . 202

CHAPTER 5. SEA WATER EXCHANGE AND FLOW CAUSED BY INTERNAL TIDES 5.1. Objectives 5.2. Sea Water Exchange Caused by Internal Tides

. . . 204 . . . 204 . . . 204

CHAPTER 6. STRUCTURES FOR MAKING WATERWAYS. . . 208 6.1. Objective . . . 208 6.2. Suitable Parameters . . . 208 6.3. Designing Waterway . . . 209 6.4. Size . . . 209 CHAPTER 7. STRUCTURES TO CONTROL TIDAL CURRENTS 7.1. Objective 7.2. Optimum Parameters 7.3. Coefficient of Discharge in the Case of Tidal Current Control Measures with a Training Wall

215 215 216 217

xix 7.4. Optimum Size and Placement of Tidal Control Structures

. . .

219

CHAPTER 8. SEA WATER INDUCTION BYWAVES ... 8.1. Objective . . . 8.2. Determining the Position of the Inflow and Outflow Openings . . . 8.3. Design Wave . . . 8.4. Design Level Based on Tides . . . 8.5.The Inlet ...

225 225

CHAPTER 9. STRUCTURE FOR CURRENT CIRCULATION 9.1. Objective 9.2. Structure for Circulation of Current by Waves 9.3. Vertical Circulating Structure Across theFlow 9.4. Changes in Topography and Bottom Matter Caused by Structures Giving Rise to CirculatingCurrent CHAPTER 10. IMPROVEMENT OF WATER QUALITY USING MECHANICALENERGY 10.1. Objective 10.2. Optimum Parameters 10.3. Air Bubble Curtain (A.B.C.) 10.3.1. Flow conditions because of A.B.C. when there is no dense layer 10.3.2. Increase in DO due to A.B.C. 10.3.3. In cases where layer is dense 10.3.4. Required horse power 10.4. Expelling of Lower Bed Layer of Water with a Pump 10.4.1. Determination of the quantity of water to be expelled 10.4.2. Diversion structures 10.4.3. Pump 10.4.4. Guiding and discharge channel 10.5. Guiding Open Sea Water into the Bottom Layers with a Pump 10.5.1. Determining the quantity of water to be guided 10.5.2. Water diversion structures 10.5.3. Pump and pump station 10.5.4. Water conveying channel 10.5.5. Water release works

225 226 227 227

... . . . . . . . . .

236 236 237 240

. . .

243

... . . . . . . . . .

245 245 245 246

. . . . . . . . . . . . . . .

247 250 253 254 259

. . . .

. . . .

. . . .

259 260 262 263

. . . . . .

. . . . . .

. . . . . .

265 265 265 266 266 267

XX

CHAPTER 11. ESTABLISHMENT OF SUBSTRATE STRUCTURES FOR ADHESION 11.1. Objective 11.2. Stability of Adhesive Substrate

. . . 269 . . . 269 . . . 269

CHAPTER 12. IMPROVEMENT OF QUALITY OF BOTTOM MATERIAL 12.1. Objective 12.2. Sea Bathymetry and Formation of Bottom Material 12.3. Improvement of Tidalflats 12.4. Improvement of Sand Bay 12.5. Improvement of Dipping Reef Belt

... . . . . . . . . . . . . . . .

273 273 273 274 280 286

CHAPTER 13. WAVE DAMPENING BREAKWATERS 13.1. Definition 13.2. Function 13.3. Types of Wave Dampeners 13.4. Gravity-type Wave DampeningBreakwaters 13.4.1. Structure of gravity-type wave dampening breakwaters 13.4.2. Function and features 13.4.3. Design conditions 13.4.4. Orientation of breakwater in relation to the direction of wave approach 13.4.5. Determining the height of the top of breakwaters 13.4.6. Force acting on the breakwater 13.4.7. Determining the cross section 13.5. Floating Breakwater 13.5.1. Structure of the floating breakwater 13.5.2. Characteristics and application conditions 13.5.3. Design conditions 13.5.4. Degree of calmness and orientation of floating breakwaters in fish culturing area 13.5.5. Characteristics of dampened wave 13.5.6. Anchorage 13.5.7. Structure and strength of materials 13.6. Other Wave Dampening Systems

... . . . . . . . .

289 289 289 290 291

. . . ... . . . . . . . . .

310 311 314 324 326

CHAPTER 14. BREEDING FACILITIES 14.1. Nets 14.1.1. Objectives 14.1.2. Optimum parameters

... ... . . . . . .

332 332 332 332

. . . .

. . . 291 . . . 292 . . . 293 . . . . . . . .

. . . . . . . .

. 293 . 294 . 298 . 298 . 308 . 308 . 308 . 309

xxi 14.1.3. Hydrodynamic forces acting on nets 14.1.4. Framed breeding facilities 14.1.5. Stick net facilities 14.1.6. Enclosure net, partitioned net 14.2. Suspended Cultivation Facilities 14.2.1. Objectives and structure 14.2.2. Maximum vertical and horizontal forces acting on each suspension 14.2.3. Calculation of cross section of beam used in raft-type facility 14.2.4. Size of raft 14.2.5. Tension on the anchor rope of the raft CHAPTER 15. IMPROVEMENT OF ESTUARINE AREA 15.1. Objective 15.2. Mechanism of River Mouth Closure 15.3. Construction Methods to Prevent Closure of River Mouth

332 335 341 343 348 348 349 352 355 356 360 360 360 367

APPENDIX 377

PART 1

GENERAL RULES

CHAPTER 1

GENERAL RULES

1.1. Objective of the Manual This manual, based on the codes for development of coastal areas, is a guidefor planning, designing and adopting appropriate construction techniques for coastal fishery projects, and the objective of the manual is to highlight the concerned aspects so that the designs can be carried out appropriately with ease and accuracy. ft

Explanation The projects undertaken for the development of coastal areas propose to improve and create new facilities for landing marine produce along the coastal zone/coast. The area covered is the ocean space from the surface to the floor of the ocean. Engineering expertise available is rather poor for the zone covering 0 to 200 m water depth. The development is being undertaken by organizations ranging from urban and rural prefectures and municipalities to fishery associations and cooperatives. These organizations would not find it easy to have functional plans and designs of projects, if the personnel are to plan and design the facilities independently. Therefore, this manual for planning and designing projects intends to present the most appropriate and economic designs. 1.2. Relationship with the Local Environment Depending upon the manner in which the projects and construction works are executed they can have detrimental effects on the ocean and ocean environment. Explanation The seashore and the sea are always in a process of dynamic equilibrium. If any artificial change is introduced a new equilibrium process emerges which results in changes in land forms, water quality and the environment. Adequate precautions should, therefore, be taken to ensure that no adverse effects take place on coastal environment results due to either creating a natural habitat for breeding, or providing a channel for navigation of vessels or establishing any type of fishery industries, etc.

4 1.3. Framework Prescribed in the Manual Theframeworkprescribed in this manual gives the specifications and usage of appropriate materials and designs to prevent damage due to natural disasters in developmental projects for coastal fishery areas. Plan to bring a separate manual based on biological data is under consideration and will be published separately. Explanation The projects for development of coastal fishery areas should necessarily be based on an understanding of the behavioral characteristics of the concerned organisms and assist or improve them environmentally. This methodology is being adopted to identify the environment required for culture of these organisms and to develop technologies for creating the required environment. The manual stipulates the engineering requirements for design of structures of these development projects, which have been approved. The codes stipulate the quality and strength of structures. In this manual surveying methods and construction methods have been dealt with separately.

Investigation of site conditions

Survey of methods of development

Design survey

f ----------------j Design of structures

Estimated effectiveness

i-------- 1| Specifications l___

| provided by I the manual

j Execution] U>f design J

5 1.4. Relationship with Other Development Projects in the Region Coordination with other development projects in the area is necessary for stipulating optimum utilization of different types of areas along the coast and in ocean zones, for conserving the coastline, harbor estates, fishery port areas, approach channels, etc. Explanation For utilization of the aforesaid coastal and ocean zones there are codes established, respectively, for them and besides following them, during and after the construction, a great deal of cooperation among various organizations is necessary for optimum utilization of the ocean zone.

PART 2

DESIGN CONDITIONS

CHAPTER 1

DESIGN WATER LEVEL

1.1. General To determine the design (still) water level to be adopted in the design of structures, which have to withstand the action of sea waves (against them), the factors to be considered are changes in water levels due to tides, storm surges, tsunamis, etc. Explanation The basic facts related to water levels of the sea are given below: 1. Mean Sea Level (MSL) or Mean Water Level (MWL) 2. Chart Datum Level (CDL) 3. Highest Water Level (HWL) (astronomical high tide) Lowest Water Level (LWL) (astronomical low tide) 4. Higher High Water Level (HHWL) Lower Low Water Level (LLWL) 5. Mean Sea Level (Tokyo Bay) (TP) 6. High Water/Tide Levels at all times other than during cyclones, typhoons, tsunamis, and other natural calamity In Fig. 2.1.1 designations regarding sea levels are shown. In the figure Hm, H„ Hk, Ha are the water level variations which correspond to the 4 important astronomical tidal constants (M2, S2, Klt Ol). The still water level of sea will be determined by the actual highest water level of sea or the calculated value [HWL + (variations)] of the water level due to conditions of high tide, tsunami, etc., based on the functional design of the facility and adopting the appropriate materials and design for prevention of damage due to natural calamities. However, the still water level of tidal lakes where the tidal effect is not great, the influence of the water level will be determined with water-level records.

10

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Highest Water Level (astronomical high tide) HWL Higher High Water Level (springs) HHWL ■ Mean High Water Level (springs) MHWL Mean High Water (neaps) Mean Sea Level (MSL) Mean Sea Level (Tokyo Bay) (TP) Mean Low Water Level (neaps) Mean Low Water Level (springs) MLWL Lower Low Water Level (springs) LLWL Lowest Water Level (astronomical low tide) LWL Chart Datum Level (CDL)

£ + £ +

a?

+ af n

2D 8© 3: E i af T©5 © n © z

Spring tide difference 2 (Hm + HJ

Fig. 2.1.1. Relationship between various tide levels.

1.2. Calculation of Tide Levels Calculation of tide levels according to ebb and flood, will be done after determining the ebb andflood constants using actual measured data (oscillation and the angle of lag of tidal characteristics). However, when this is not possible the same will have to be arrived at using revised numbers (spring tide revised number, neap tide revised number and high tide revised number) based on observed values at standard sites (or what can be considered standard tidal stations) which have similar tidal periods and characteristics. Explanation 1. Observation Observations of continuous changes in sea water levels are called tidal observations and automatic tide gages of a float or pressure type are used. Observations of tide waves at a particular site should be carried out over a minimum of a year in order to fully understand tidal ranges at that site. If there is a nearby tidal observation station in the appropriate ocean zone, revised values can be obtained by observation for not less than 14-hour period covering one high and low tide preferably of a spring tide cycle. 2. Sea Water Levels, and Sea Water Level Calculation Based on Tidal Flow Constants i) Determination of tidal flow constants (short-term absentation) For calculating the sea level, tidal flow constants of the 4 main tidal categories (M2, S2, Kh Of) are necessary, and for obtaining these constants

D

© a: e

+

i tE C » CL C/)

11 at a place, a minimum of 15 days, observed data are necessary. The observed tides ate actually shown as the total of the tidal categories. By calculation, the individual tidal categories can be separated and, as the amplitude and virtual mass of the individual tidal categories culminate, the time it takes for the highest tide of the tidal category is shown by the phase angle (this is referred to as the angle of lag). Deriving this angle is called harmonic analysis and from the observation of tides in different areas the harmonic constants can be obtained. ii) The chart datum Determination of a suitable datum, depending on the objective of the enterprise, is desirable. Arriving at a chart datum to which all levels can be referred (obtained from the mean sea level by subtracting half the tidal differences of the 4 tidal categories M2, Kh Ot from mean sea level). iii) Sea level calculation according to the use of revised (constant) based on observed values of standard bays or tidal observation stations The revised constants for important coasts are given in hydrographic survey charts and the tide tables but, for ocean zones which are not included, the revised constants are arrived at, as given below, after a 15-day tidal observation of high and low waters. a. Determination of revised constants Revised constants according to the following formula: Flood tidal period revised constant = (MHWI) - (MHWI)o

(X-Xo)

(2.1.1) 31 Ebb tidal period revised constant = (MLWI) - (MLWI)0- _ (X - Xo) Here MHWI and MLWI are, respectively, the average of high tide and of low tide. Xindicates the east longitude by time unit (1 h/15°). The subscript 0 stands for the standard bays or standard tidal observation station. Where the daily tidal variation is very large, for convenience, in place of MHWI and MLWI the recurrent tide (ebb and flood when the moon is farthest from the Equator) average high-tide range, and the average low-tide range are used. High tide revised number is according to the following formula: High tide revised number = ^igh difference) (high tide difference)0

(2.1.2)

12 where the daily tidal variation is very large, in place of high tide the average tidal difference of the subsequent tide should be used. b. Calculation of tide level Flood tide time = (flood tide time)0+(flood tide revised number) Ebb tide time = (ebb tide time)o + (ebb tide revised number) Flood tide level = (flood tide level - average tide level)o x high tide revised number + (average tide level); Ebb tide level = (ebb tide level - average tide level)o x low tide height revised number + (average tide level)0

(2.13)

(2.1.4)

CHAPTER 2

WAVES

The ocean waves are of oscillatory type and may vary from ripples or surface tension waves of less than a 1.0 sec period to tide waves of about 12 hr period. In this manual, waves mean the normal gravity waves of 1-30 sec period which influence the design of port elements. In the design of coastal and off­ shore/near shore structures one has to decide the various characteristics of the wave such as height, period, and direction of approach at the site. If the various characteristics of the wave govern the design of the maritime structure/port element, then various hydraulic conditions like tidal flow, rise in water level, change in water pressure, etc. which also influence the design, should be considered. To ensure that the construction elements used in the design are safe against failure due to natural calamities and functionally effective, determination of the parameters of the waves that are likely to occur at the site is necessary. 2.1. Computing Deep Water Waves 2.1.1. General To design structures to withstand the forces of waves which occur in deep water and the various wave characteristics that affect the structures at the selected site, the following two points must be considered and a decision be made. 1. Protection of the facilities against failure due to natural calamities. 2. Objectives of the facilities. Explanation 1. The various characteristics of waves must be based on reliable observed values or an established method of computation. These waves will, in principle, indicate the significant waves (1/3 of the highest waves). 2. Computation of the design wave is normally carried out as shown in Fig. 2.2.1. A wave in the open sea is defined by its height and period. These are, respectively, the significant wave height and period. The direction of wave

Actual mea­ surement of wave characteri­ stics

Calculation of wave charac­ teristics

Calculation of deep-water design wave

Assumption of probability of waves occurring Reobservation period

(D Deciding deep-water design wave

Refrac­ tion

Refraction + diffraction

(D Diffrac­ tion

©

Reflec­ tion

Friction, etc.

z z n r . ©

Calculation of unrefracted deep-sea wave

Deciding calculated deep (sea) water wave

Change only due to water depth

Calculation of change in form of wave because of water depth

Breaker wave height, water depth at breaker zone

©

Change in wave height after breaking

i 1

©

r ^

1

1

Design wave in front of the structure (Natural calamities)

\

J

©

f Design wave used L for design of structures (Objectives)

Fig. 2.2.1. Procedure for calculating the design wave.

'

approach is variable. Calculation of variable directions of approach of waves is done by applying thumb rules and, in the case of energy, they are summed up. 3. The deep-water wave used in the design differs depending on the function of the facilities; whereas the biggest significant wave is considered in order to account for safety of structure against wave. (The actual computation of waves is shown in Section 2.1.4.) When considering utility it is necessary to use the highest multi-frequency of the significant wave (actual calculation method shown in Section 2.1.3) that may occur during the life time of the facility of the structure. 4. The significant wave (//1/3, J 1/3) is the potential idealized probable wave based on a statistical index of a nonregulated group of waves. This value of the significant wave is close to the value of a visually observed wave. The value can be used in the computation of storm surges. Further, the period of the specific wave is generally assumed to be the one equal to the period represented at the peak of the wave spectrum. In view of these advantages, the significant wave is used, in general, as the representative wave from among a group of waves. Commencing with the significant wave the assumptions made regarding various characteristics of waves that are to be used in the design of structures for coastal development projects are as given below: a. Significant wave (//1/3, J 1/3): In a given group of waves (in obser­ vations of over 100 continuous waves, this definition under b, c is the same) counting from the highest wave height, selecting the highest 1/3 of the total waves counted, and taking the average value of their wave height and period. This is called the probable significant wave height and period. b. 1/10 highest wave (//yio, Tmo): The average of the highest 1/10 of all the waves in a group for a given time period. c. Average wave (//, T): In a given group of waves the value of the average wave height and period of all the waves would be the average wave height and period. d. Highest wave (Z/max, Tmax): This is the highest wave within a group of waves for a specific period of time. e. Deep water significant wave height (//0, T0): Waves which occur in a water depth greater than 1/2 their surface wavelengths exhibit various characteristics of the deep water significant wave. f. The deep water wave height (Ho): Equivalent to an observed shallowwater wave (at an area of interest) if the wave was unaffected by refraction and bottom friction. Here, the symbols in parenthesis show the height and period of waves. The relationship between the various wave heights are:

16 = 1.07 V Iog A ^ 2.0

“ 1/3 where JV is the number of waves observed. 5. The unrefracted deep water wave height is given by the following formula. As a large number of the deep water waves in the wave formula, chart, etc. have been observed in straight water channels it is necessary to use an unrefracted deep water wave corresponding to these waves: (2.2.1)

(2.2 .2) in general, we have Ho = KaK, H0

(2.2.3)

Here Ks : Shoaling coefficient (see 2.3.2. Changing forms of shallow water); Kd : Coefficient of diffraction (see Section 2.3.4. Diffraction of waves); Kr : Coefficient of refraction (see Section 2.3.3. Refraction of waves); Kf : Coefficient of friction; Kh : Shoaling coefficient at breaker position; and H : The wave height at the site under consideration. 6. One large wave which occurs because of some unusual atmospheric phenomenon is termed an extremely large wave. 7. While designing aquiculture areas it is necessary to compute the wave height (as in 1-16 in Fig. 2.2.1) for those facilities built in deep-water such as fish bank, etc., calculating deep water waves is not necessary but to carefully considering the characteristics of the ocean zone and the site conditions for locating the facilities is necessary. 2.1.2. Basic characteristics of waves The basic characteristics of waves such as wavelength, wave height, wave celerity, etc. can be calculated based on the small-amplitude wave theory. In case approximation turns out to be inadequate the computation should include the effect of the finite amplitude of the waves. However, computing the basic characteristics of wave components from the small-amplitude wave theory is desirable, when adding up various elements in irregular wave groups becomes necessary. Explanation The basic characteristics like wave height and wave period change with water depth and the slope of the seabed. In small-amplitude wave theory, wave

17 height, speed of water particles, etc., of the wave axe not guided by the factors mentioned under shallow water waves compared to those under wavelength, because the height of the wave is small in relation to water depth. Compared to the small-amplitude wave theory the finite amplitude wave theory presents a picture closer to the natural wave than that of the small-amplitude wave theory. 1. Small-amplitude Wave Generally, the small-amplitude wave, according to the ratio of the water depth h to wavelength L (h/L: comparative water depth) is divided into three types. The coordinate system of the formula is given below in Fig. 2.2.2. 1) Wavelength (for h/L < 1/25) i) Waveform (22.4) where H: wave height; L: wavelength; and T: wave period, ii) Wave celerity and wavelength C = yfgK,

L = VgH T

(22.5)

where g: acceleration due to gravity; and h: water depth, iii) Local velocity and acceleration at a point in the fluid Horizontal component: h

’

dt

h dt

(2.2.6)

Vertical component: (2.2.7) ’Direction of wave propagation

h-ff -H *™W 7777777------------- W

lu.mrjr i/mm —

Fig. 2.2.2. System of coordinates.

18 iv) Subsurface pressure at any point (2.2.8)

p = w0 (£ - z) Here w0: Unit weight of sea water. 2. Shallow Water Waves (for 1/25 < h/L < 1/2) i) Waveform r H . (2k 2jt , £ = — sin — x - — t 2 \ L T

(2.2.9)

ii) Wave celerity and wavelength (2.2.10)

c = l»/Oftt tanh ^ 2it L

2k

(2.2.11)

L

iii) Velocity and acceleration at a point in the fluid Horizontal component: xH cosh 2x (z + h) L . I 2x 2x A u- — . , ^ , ,r 7 sm — x - — t\ T sinh 2xh/L \ L T J

(2.2.12)

du 2k2H cosh 2k (z + h)/L (2 x 2k — = --------------------1------ L— cos — x ----dt T2 sinh 2xh/L \ L T

(2.2.13)

Vertical component: kH sinh 2ji ( z + h ) L /■ , ' T smh2xhL

w = - — -----------. ,

COS

(2 k — \ L

2k \ t\ T I

X - —

dw 2k 2H sinh 2jt (z + h)/L . ( 2k in — x — = ------------------- L------L— sm dt T2 sinh 2jih/L \ L

2k \ n T )

(2.2.14) (2.2.15)

iv) Subsurface pressure at a point in the water wqH cosh 2ji ( z + h)/L I 2k 2k f = cosh 2 jt/ i/L sl" ( T x ~ T ') + ^

(2.2.16)

v) Total average energy of a wave per unit surface area E^^woH2

(2.2.17)

19 vi) The group velocity of energy transported „ 1I 4nh/L Cr = nC = - 1 + 2 \‘ ’ sinh 4jth/L

2jt

ta n h ^ L

(2.2.18)

vii) Average unit of energy transported across unit width in unit time W = CqE 4nh/L l6 Woffi (X + sinh 4nh/L

2it

tanh

2tth L

(2.2.19)

3. Deep Water Wave (1/2 < h/L). The various formula for deep water waves can be obtained by substituting sinh 2jih/L = cosh 2jih/L = e2xh/L and tanh Inh/L = 1 in the various formulas for shallow water waves. Generally, the wave height, wavelength and wave period for deep water waves are denoted, respectively, by Ho, L0 and T0. 2.1.3. Method of determining various characteristics of the deep-water wave in the design The various characteristics of the deep water wave used in the design determined by the following procedure: R eliable actually m easured values used fo r existing structures in the established ocean zones where structure facility is pro p o sed

(When avail­ able)

in

w below (When available)

(When not avail­ able)

Reliable actually m easured values in the vicinity o f ocean zone where structure is to be located

A s in (2) below (When not available) A s in (3) below

Explanation 1. When actual, reliable measured values are available for existing structures in the ocean zones: The actual measured values of wave height and period which occur in the ocean zone at sites where structures already exist are statistically analyzed. Depending on the conditions at the site and requirements of the structure the probable highest wave force the structure may have to withstand can be arrived at. By studying the size of any existing structure or protective work in the close vicinity that has well withstood the wave forces over a period of time,

20 Table 2.2.1. Wavelength and wave celerity dne to water depth and wave period Wave period 4

3

5

6

Wave­ Wave Wave­ Wave length celerity length celerity (m/s) (m) (m/s) (m)

Wave­ length (m)

Wave celerity (m/s)

219 3.07 3.73 4.26 4.72

15.39 21.62 26.28 30.14 33.46

220 3.09 3.75 4.31 4.78

30.71 3283 34.75 36.49 38.07

5.12 5.47 5.79 6.08 6.34

36.37 39.03 41.42 43.61 45.63

5.20 5.57 5.92 6.23 6.52

6.43 6.73 6.97 7.16 731

40.84 43.18 45.20 46.89 4838

6l81 7.20 733 7.82 8.06

49.24 5238 55.15 57.60 59.80

7.04 7.49 7.88 8.23 834

7.52 7.64 7.71 7.75

50.69 5238 5337 54.42 54.99

8.45 8.73 8,93 9.07 9.17

63.46 6636 6863 70.49 71.91

9.06 9.48 9.81 10.07 10.27

73.50 74.23 75.03 75.41

1030 10.61 10.72 10.77

76.43

10.92

Wave­ length (m)

Wave celerity (m/s)

Wave­ length (m)

Wave celerity (m/s)

0.5 1.0 1.5 2.0 2.5

6.39 8.69 10.22 11.30 1210

213 2 90 3.40 3.76 4.03

8.67 11.89 14.37 16.22 17.71

217 3.00 3.59 4.05 4.43

10.92 15.23 18.40 20.94 23.10

218 3.05 3.68 4.19 4.62

13.16 18.44 2237 25.58 28.31

3.0 3.5 4.0 4.5 5.0

1268 13.10 13.40 13.61 13.76

4.23 4.37 4.47 4.54 4.59

18.95 19.99 20.84 21.58 2218

4.74 4.99 5.21 5.39 5.55

24.91 26.52 27.93 29.18 30.29

4.98 5.30 5.59 5.84 6.06

6.0 7.0 8.0 9.0 10.0

13.92

4.64

23.12 23.76 24.19 24.47 24.65

5.78 5.94 6.05 6.12 6.16

3217 33.67 34.86 35.81 36.56

24.84

6.21

37.61 38.22 38.57 38.85

Water depth (m)

12.0 14.0 16.0 18.0 20.0

7

23.0 25.0 28.0 30.0 35.0 40.0 45.0 50.0 55.0 60.0 65.0 70.0 75.0 80.0 90.0 100.0 120.0 Deep-water wave

14.04

4.68

24.%

6.24

38.99

7.80

56.15

9.36

21

Wave periods 8

9

10

Wave­ Wave Wave­ Wave length celerity length celerity (m) (m/s) (m) (m/s)

Wave­ length (m)

11

Wave Wave­ celerity length (m/s) (m)

13

12

Wave celerity (m/s)

Wave­ length (m)

Wave celerity (m/s)

Wave­ Wave length celerity (m) (m/s)

17.62 24.78 30.19 34.70 38.56

2 22 3.10 3.77 4.33 4.82

19.84 27.94 34.08 39.19 43.63

220 3.10 3.79 4.35 4.85

2207 31.10 37.95 43.68 48.67

221 3.11 3.79 4.37 4.87

24.27 34.23 41.80 49.06 53.69

221 3.11 3.80 4.46 4.88

26.53 37.37 45.66 53.63 58.69

221 3.12 3.81 4.47 4.89

28.71 40.54 49.53 57.10 63.69

2.21 3.12 3.81 4.39 4.90

4201 45.13 47.98 50.61 53.05

5.25 5.64 6.00 6.33 6.63

47.58 51.18 54.48 57.53 60.38

5.29 5.69 6.05 6.39 6.79

53.23 57.19 60.92 64.40 67.64

5.31 5.72 6.09 6.44 6.76

58.61 63.16 67.33 71.20 74.86

5.33 5.75 6.12 6.47 6.80

64.15 69.11 73.69 77.98 8205

5.35 5.76 6.14 6.50 6.84

69.62 75.07 80.08 84.72 89.19

5.36 5.78 6.16 6.52 6.85

57.47 61.39 64.87 68.01 70.85

7.18 7.67 8.11 8.50 8.86

65.58 70.20 74.36 78.18 81.67

7.28 7.80 8.26 8.60 9.08

73.58 78.91 83.77 88.24 9233

7.37 7.89 8.38 8.82 9.23

81.55 87.56 93.06 98.13 1028

7.41 7.96 8.46 8.92 9.35

89.44 96.14 1023 108.0 113.4

7.45 8.01 8.52 9.00 9.44

97.31 104.6 111.4 117.7 123.6

7.48 8.05 8.57 9.05 9.50

75.82 79.96 83.36 86.30 88.71

9.48 9.99 10.42 10.79 11.09

87.86 93.13 97.75 101.7 105.1

9.76 10.35 10.86 11.30 11.68

99.63 106.1 111.8 116.7 121.2

9.97 10.61 11.17 11.67 1211

111.3 118.8 125.5 131.4 136.8

10.15 10.80 11.41 11.95 1244

1228 131.3 139.0 146.0 1523

10.23 10.94 11.58 1216 1269

134.2 143.8 1524 160.3 167.6

10.37 11.06 11.72 12.33 12.88

91.65 93.21 95.03 95.98 97.65

11.46 11.65 11.88 1200 1220

109.5 1120 115.0 116.7 120.0

1216 1244 1278 1297 1234

126.9 130.3 134.7 137.2 1424

1270 13.03 13.47 13.72 14.24

144.0 148.2 153.9 157.3 164.4

13.09 13.48 13.99 14.29 14.95

160.7 165.9 1727 176.9 186.0

13.40 13.82 14.40 14.74 15.50

177.3 183.2 191.3 196.3 207.2

13.63 14.11 14.71 15.10 15.94

1223

13.59

146.2 149.1 151.2 1526 153.7

14.63 14.91 15.12 15.26 15.37

170.1 174.5 178.0 180.7 1828

15.46 15.86 16.18 16.43 16.61

193.5 199.5 204.7 208.9 2122

16.12 16.64 17.06 17.40 17.68

216.5 224.4 231.0 236.5 241.4

16.65 17.26 17.77 18.20 18.57

154.4

15.44

184.3 185.5 186.3

16.75 16.86 16.94

214.8 216.9 218.7 220.0

17.90 18.08 18.22 18.33

245.3 248.6 251.5 253.8 257.2

18.87 19.13 19.34 19.52 19.78

259.5 2620

19.96 20.15

263.6

20.28

99.82

1278

126.3

14.04

156.0

15.60

188.7

17.16

224.6

18.72

(continued)

22 Table 2.2.1 (continued) Wave period 14

20

16

18

Wave­ Wave length celerity (m/s) (m)

Wave­ Wave length celerity (m/s) (m)

15

Wave­ length (m)

Wave celerity (m/s)

44.42 6251 76.49 88.22 98.58

2.21 3.13 3.82 4.41 4.93

Wave­ length (m)

Wave celerity (m/s)

Wave­ length (m)

Wave celerity (m/s)

0.5 1.0 1.5 2.0 2.5

30.94 43.65 53.41 61.51 68.72

221 3.12 3.82 4.39 4.91

33.13 46.81 57.23 66.00 73.65

2.21 3.12 3.82 4.40 4.91

35.37 49.91 61.09 70.48 78.62

221 3.12 3.82 4.41 4.91

39.80 56.24 68.77 79.33 88.63

2.21 3.12 3.82 4.41 4.92

3.0 3.5 4.0 4.5 5.0

75.11 80.98 86.42 91.71 96.32

5.37 5.79 6.17 6.55 6.88

80.57 86.88 9292 98.25 103.4

5.37 5.79 6.20 6.55 6.90

86.05 9283 99.11 105.1 110.6

5.38 5.80 6.20 6.57 6.91

96.97 104.6 111.7 118.3 124.7

5.39 5.81 6.21 6.57 6.93

107.9 116.4 124.3 131.8 138.9

5.40 5.82 6.22 6.60 6.94

Water depth (m)

6.0 7.0 8.0 9.0 10.0

105.1 113.2 120.6 127.4 133.8

7.51 8.08 8.61 9.10 9.56

113.0 121.6 129.6 138.7 144.0

7.53 8.11 8.66 9.14 9.60

120.7 130.1 138.7 146.7 154.2

7.55 8.13 8.67 9.17 9.64

136.3 146.9 156.9 166.0 174.5

7.57 8.17 8.71 9.21 9.69

151.8 163.7 174.7 185.0 194.7

7.59 8.18 8.74 9.25 9.73

12.0 14.0 16.0 18.0 20.0

145.6 156.1 165.7 174.5 1825

10.40 11.15 11.83 12.46 12.90

156.8 168.3 178.8 188.5 197.5

10.45 11.22 11.92 12.56 13.15

168.0 180.5 191.9 2024 2122

10.50 11.28 11.99 12.65 13.26

190.3 204.8 217.9 230.2 241.5

10.58 11.37 12.11 12.78 13.42

2126 228.8 243.7 257.6 270.6

10.62 11.44 12.18 12.87 13.53

23.0 25.0 28.0 30.0 35.0

193.6 200.2 209.5 215.3 228.1

13.83 14.30 14.97 15.38 16.29

209.7 217.2 227.6 234.1 248.8

13.93 14.47 15.17 15.61 16.52

225.7 233.8 245.6 2527 269.0

14.10 14.62 15.34 15.79 16.81

257.3 267.1 280.8 289.6 309.1

14.29 14.84 15.60 16.08 17.17

288.6 300.0 315.7 325.6 348.6

14.43 14.99 15.78 16.28 17.43

40.0 45.0 50.0 55.0 60.0

239.2 248.3 256.9 264.1 270.2

17.08 17.77 18.35 18.86 19.31

261.4 2726 2825 291.1 298.8

17.43 18.17 18.83 19.41 19.92

283.3 296.2 307.6 317.9 326.9

17.71 18.51 19.23 19.86 20.43

326.7 3426 357.0 370.1 3821

18.15 19.03 19.83 20.56 21.22

369.3 388.2 405.4 421.3 435.9

18.46 19.41 20.27 21.06 21.80

65.0 70.0 75.0 80.0 90.0 100.0 120.0

275.7 280.3 284.3 287.6 293.1

19.69 20.02 20.30 20.55 20.93

305.6 311.5 316.8 321.4 329.0

20.37 20.77 21.12 21.43 21.94

335.2 3425 349.1 354.8 364.9

20.95 21.40 21.81 22.18 22.80

393.0 4028 4122 420.5 435.4

21.83 22.39 22.91 23.36 24.19

449.3 4621 473.8 484.7 504.1

22.48 23.11 23.69 24.23 25.20

296.9 301.6

21.21 21.54

335.0 3427

22.32 2283

3728 383.9

23.30 23.99

447.8 467.0

24.88 25.94

521.0 549.0

26.06 27.43

Deep-water wave

305.7

21.84

350.9

23.40

399.3

24.%

505.3

28.07

623.9

31.19

23 the wave height or force the structure has withstood can be computed working backwards. 2. When actual reliable measured values can be obtained for the ocean zone vicinity: Adopting the same procedure as in (1) the wave height and period in the ocean zone vicinity are computed and, based on these, the various dimensions of the deep water wave to be used in the design are determined. 3. When actual, reliable measured values cannot be obtained: Based on the meteorological data in the generating area of the wave, various dimensions of the wave can be computed and determined. Note 1. Obtain the wave direction which exerts the highest force on the structure from the foregoing points 1, 2 and 3. Note 2. Obtain reliable actual measured values of the design wave for the structure which is to be designed to withstand natural calamities. A minimum of 10 years’ monthly observed data of the significant wave (wave height, period and direction) should be studied to arrive at the design wave for the design of the structures. At least more than one year’s monthly observation data on the significant waves are necessary in the absence of ten-year data. Note 3. What needs to be studied in the storm surge data are abnormal meteorological conditions over a long period (as a rule for the previous 30 years) or calculated storm surge values for potential cyclones, etc., or, as a rule, use continuous meteorological data for five years or more for the normal wave. 2.1.4. Determination of the various characteristics of the design deep-water wave The computation of percentage of occurrence at a probability number of the design deep-water wave, based on comparatively long, reliable data, is an aspect for the design of the structure. Explanation 1. For calculation of the percentage of occurrence at a probability number of the design wave height the reliable way is to statistically analyze the highest wave for each year. However, as every year a large number of wave calculations will be required, the computation work will increase and the accuracy of the wave calculation will come down. In case only one representative of the large wave is considered for a given period of T years considered as life of the structure for design then carry out the wave computation selecting certain meteorological conditions almost similar to the period of T years. When using short-term observation data select a wave height value after dividing the data into groups of 20 or 30. 2. In statistical treatment arrange the wave heights in order of height and

24 for waves above any given value calculate the number which exceeds this height. If the total number of observed data is N , and mth order wave is represented then P , the probability of waves, affecting the structures, which are equal or smaller than s is calculated as follows: (2.2.20)

P [ H s x m>N] = l -

In the formula, use the values a and p for each probability distribution coefficient as given in Table 2 . 2 . 2 . As a theoretical distribution coefficient cannot be obtained for a probable wave height, apply the Gumbel, Weibull or any other distribution coefficient and obtain the one most appropriate for the data. Apart from the correlation formula, the probable wave height can also be arrived at from the various return periods. For the period corresponding to the probable wave height, plot the wave height and period from the data of the highest wave, which is the assumed data of the probable wave, and arrive at a suitable value for the wave height based on the corresponding relationship. 3. To apply distribution coefficient, from the probability P in the formula w i'h T, ( = ^

:

- I n { - In P [ H % -* ]} (Gumbel distribution) ( 2 .2 .2 1 ) Yv = [ - I„{1 - P[H 1 *]} ]1/K (Weibull distribution) (2.2.22) If the data correspond completely with formula ( 2 . 2 . 2 1 ) or formula ( 2 . 2 . 2 2 ) then there is a direct relationship between x and y,,. However, if for the data the direct relationship in formula ( 2 . 2 . 2 3 ) is applied, then after determining the coefficient (A, B) by the method of the least squares, the assumed formula for the probable wave height can be obtained Yv =

Table 22.2. Parameters for calculation of least probability Distribution coefficient

a

P

0.44 0.54 0.51 0.48 0.46 0.44 0.42 0.39

0 .1 2

0.64 0.59 0.53 0.50 0.47 0.42 0.37

Thomas plot

0 .0 0

1 .0 0

Hazen plot

0.50

0 .0 0

Gumbel distribution Weibull distribution -do-do-do-do-do-do-

0.75) 0.85) = 1.0) = 1.1) = 1.25) = 1.5)

(k = (k = (K (K (k (K

(K = 2 .0 )

25 x = A yv + B A

(2.2.23)

A

whereA and B are the computed values obtained from the distribution coefficient parameters A and B of the Gumbel and Weibull distributions. 4. If Rp, the return period of wave height in the relationship P[H 1 x] is known then the least probability P [H £ x] can be obtained from formula 2.2.24. RP = — N 1- P [ H ^ x ] or (2.2.24) P[H$x] = l - - £ — N RP Here K is the period in years for which the analysis has been made, and N is the data number. 2.1.5. Computing unrefracted deep-water wave height Computing unrefracted deep-water wave height involves the following formula, arrived at by considering the observations of wave heights at the water edge o f the proposed characteristics according to the direction of wave approach taking into account the bed friction and the changing form of the wave due to refraction and diffraction: H= tfo

y LDi (K riK JC fcf KsHq (2.2.25)

=H/K,

In general, we have

/f o=V^

1 1=0

H0

(2.2.26)

Here Ho : Unrefracted deep-water wave height; H : Wave height in front of proposed structure; Ks : Shoaling coefficient; Di : Rate of distribution of energy, directionwise (Fig. 2.2.3); Kri : Refraction coefficient, directionwise; Kdi : Diffraction coefficient, directionwise; Kfi : Sea bed friction coefficient, directionwise; Kbi : Modified breaker coefficient, directionwise; Ho : Deep-water height; and n : Number of segments, directionwise.

26 Explanation 1. Various tide and water levels should be considered to arrive at the changing forms of the wave once it reaches the shallow-water zone. 2. Resultant direction of the wave is obtained by vectorial summation of the various wave directions. 3. When there is no diffraction IQ = 1. 4. In case a breaking wave changes to non-breaking condition, consider IQ, Kb. 5. For a long shallow beach consider Kf. 6. Under normal conditions consider segments in 3 directions and in case of complex conditions consider segments in 7 directions. 2.2. Computation of Design Wave 2.2.1. General In computation of a design wave using an appropriate method of calculation is necessary. The computation should mainly be divided into the following two stages and carried out: 1. Establishing the wind field; 2. Computation of the development and decay of the wave. Explanation 1. The place where the wave generates and is developed is called the wind field. The various parameters of wind field are: wind speed, wind direction, fetch and the period for which it blows. When the wind parameters are established, using the most appropriate calculation method for the conditions in the wind field, the development and decay of the wave can be computed. 2. The wind field can be established by: a. Using the surface synoptic chart giving the meteorological data; b. Determining the period of calculation for the case under consideration; c. Calculating the gradient wind from the synoptic chart; d. Assuming the hurricane/surface wind from formulas, experience or data obtained from actual measurement; e. Constructing the wind field. 3. In the synoptic chart, as a rule, a six-hour interval (at 3, 9, 15 and 21 hr) is used and of this the 9 and 21 hr synoptic charts published by the meteorological department are normally used. The 3 and 15 hr synoptic charts, which have recorded the continuity in change of meteorological conditions with time (for instance, the path of progress of a typhoon or a low pressure area) are used after corroboration with the aforementioned synoptic chart. The meteorological data to be collected are wind direction, wind speed

27 and atmospheric pressure. The data on wind direction and wind speed can be used for estimating the surface winds of the gradient wind. Data on atmospheric pressure are necessary for estimating the pressure distribution within the zone of typhoon. This is based on actual measured values ofatmospheric pressure within the zone of typhoon and is often used to obtain and fixthe constants used in the Fujita formula and the Myer formula: p = p- pc; and Pa, : Pressure at r -*■ «, /?„=/> / y L q > 0.015 0.015 ^ H q/Lq

7 segments (it = 7)

0°

22.5°

45.0° 67.5°

0.21 0.23

0.26 0.38

0.21 0.23

0.11 0.06

0.05 0.02

0.18

0.60

0.18

0.02

0.00

-67.5° -45.0° --22.5°

-45.0°

0°

45.0°

0.26 0.17

0.48 0.66

0.26 0.17

0.05 0.02

0.11 0.06

0.06

0.88

0.06

0.00

0.02

c. For calculation of speed of the gradient wind using the nomograph given in Fig. 2.2.3 is convenient. In the graph it is assumed that pfl = 1.1 x 10-3 g/cm3. As an example, if at 40° latitude the isobar interval is put at 2 mb which corresponds to 0.6° of latitude, then the radius of curvature of the isobar corresponds to 6° (low atmospheric pressure). In Fig. 2.2.3 joining A (0.6 mb) and B (lat. 40°) by a straight line and the curve line whose radius of curvature r = 6°, the point C can be obtained by intersection. By reading the point against the (right-hand side) vertical line the speed of the gradient wind is obtained as about 21.5 m/sec. 6. The calculation of the surface wind from the gradient wind is carried out in the following manner. a. The actual speed of surface wind is, in general, lower than the value calculated from the gradient wind formula. The direction of the gradient wind

29 A7

is, theoretically parallel to the isobar but, actually, as shown in Fig. 2.2.4, blows at an angle a to the isobar. In the Northern Hemisphere, geostrophic winds around a center of low pressure blow towards the center in anti/counter clockwise direction (cyclonic) and around a center of high pressure geostrophic winds blow away from the center in a clockwise direction (anti-cyclonic). The relationship between the gradient wind and the surface wind varies depending upon the latitude and, on an average, is considered as shown in Table 2.2.1. However, this is one standard but for surface wind calculation the actual measured value at the coast and the observations from ship at sea recorded in weather maps should be used to arrive at a reasonably correct calculation of the surface wind.

30

Fig. 2.2.4. Wind directions around high pressure and low pressure areas (Northern Hemisphere).

b. The wind speed in (5) is based on the standard value at 10 m, above the ocean surface while the wind speed obtained by the weather bureaus is less than 10 m, above the surface. However, if observed values are used to calculate the ocean wind, in case the height of the structure is very different from the height given above, then the accuracy of the wind speed must be confirmed by observations. The distribution of the wind speed along the vertical is normally shown in log scale but in design calculations of various structures an exponent is used: t/1o = £/o(10//io)1'7 (2.2.30) where h0 : Height, above sea level and the wind velocity observation point (m); and U0 : Wind velocity at the observation point (m/sec). 7. As given in Section 2.2.2 for computation of wave characteristics in the generating area, use the wave forecasting curves or graphical analysis. Construct a wind field graph in the following manner: Check whether the difference in angle between the main direction of the wave and the wind direction at the point of interest lies within 30°. In that case, the wave characteristics in the main direction of the wave automatically include the wind speed factors. 8. In case of numerous calculations for the wave computation the wind field is used in the following manner. Firstly, divide the fetch into a grid, plot the respective atmospheric pressure on the grid and calculate the direction and speed of the gradient wind. Mark the wind direction and wind speed values on the grid points and within. The limits of the wind field get automatically established by lowest wind speed and last change wind direction. 20°

a

24°

20°

0.51

0.60

Vo/Vg

40°

LA

10°

oo

Latitude

oo

Table 2.2.4. Relationship between surface wind and gradient wind (latitude-wise)

18°

17°

15°

0.64

0.67

0.70

Note: Vq : Surface wind velocity (m/sec); Vg : Gradient wind velocity (m/sec); a : Angle formed by the surface wind direction with the isobar (degree).

31 2.2.2. Computation of a wave from its generating area The wave computation is standardized by use of the significant wave method Explanation 1. General a. The significant wave method is a composite method based on the concept of the significant wave and its method of calculation first advanced by Sverdrup and Munk and modified by Bretschneider as the S-M-B method.

Fig. 2.2.5.

32 This was extended to apply to general wind field by Wilson and for waves in shallow water using numerous calculation methods of estimation by Bretschneider, Sakamoto and Ito. b. As a method of estimation, the first is the P-N-J (Pierson, Neumann and James) method and there are also the Walden method, Derbyshire method, etc. The computation procedures for these methods do not differ greatly from the aforementioned significant wave method and the computed result is generally shown as a significant wave. The significant wave method is not much different from the others and is closely associated with them. However, when the applicability of these methods is to be verified with the actual measured values, they may be used in place of the significant wave method.

Wind speed U (m/sec)

2. S-M-B Method The calculation procedure for the S-M-B method is as follows: The S-M-B method is suitable when there is no movement of the wind field due to the wind speed, blowing time and fetch within the wind field.

Fetch length F (km) Significant wave height

Significant wave period

h 1/3

r i/3

(m)

-----------Minimum duration of

wlnd f (hr)

Fig. 2.2.6. Wave forecasting curves by S-M-B method.

"Equivalent (H1/3, 7 1/3)2 = const

energy line”

33 S TA R T

iI

(1)

Synoptic chart

(2) Determination of wind field

(3) Delineating the wind field

(4)

1

Determination of wind speed ( 5)

Plot of wind field map ( 6)

Graphical analysis: is there a decay distance? (H r, T r )

Obtain direction of constant (D) if required

Hr: Wave height obtained by graphical analysis Tr: Wave period by graphical analysis Hd : Wave height at edge of decay distance Td : Period at the edge of the decay distance £>. Decay distance Hq : Wave height at deep water T0 : Wave period at deep water

NO

Ho = H f T o - Tf

.YES (7) Calculation of wave decay time

H r , Tr, D ,H d, Tn

H o = |

H t+ H d

END Fig. 2.2.7.

Using Fig. 2.2.6 the wave height and wave period of the significant wave in the deep water is calculated. The values of wave height and wave period to be used for calculation are lesser of the following: namely wind speed and blowing time or those from the wind speed and fetch. Figure 2.2.6 is based on formula 2.2.31 as revised by Wilson, in 1965, and formula 2.2.32. In case there is a change in wind speed the equivalent energy moves along one line to a new wind speed value and from this point the continuous period of new wind speed value is added. The fetch distance at this point is compared with

34 the size of the wind field, the wave height and wave period, corresponding to the lower values are obtained. In case of a change in the wind direction use the Wilson method. 1 (2.2.31)

1

(2.2.32)

Here H\[$ : Significant wave height (m); Ty3 : Significant wave period (sec); U : Wind velocity (m/sec) at 10 m, height above sea/ocean surface water surface; g : Acceleration due to gravity (m/sec2), g = 9.8 m/sec2; F : Fetch (m). 3. Wilson Method The procedure for calculation of wave characteristics by Wilson method is given in Fig. 2.2.7. The Wilson method is an improvement on the S-M-B method to make it applicable to moving wind fields such as typhoons. From the plot of Hm - t - F - T m shown in Fig. 2.2.8 determine the wave height and period by following the F - t graph, the / / 1/3 - F graph and the t graph. Figure 2.2.8 has been obtained from formulas (2.2.31) and (2.2.32). However, the unit for J1/3 is sec, and for / / 1/3 is m. 4. Calculation Method for Shallow Water Areas (Bretschneider method) In the Bretschneider method the influence of the water depth (loss of energy due to sea bed friction) in the propagation of waves is considered. For the Bretschneider method use Fig. 2.2.9, when the water depth is uniform and Fig. 2.2.10 when the sea bed slope is uniform The wave height of the significant wave can be determined as a function of wind speed and fetch. The significant wave period has a very close relationship with the wave height of the significant wave as seen in formula (2.2.33): r i/3 = 3.86 VH1/3 (2.2.33) 2.2.3. Calculation of characteristics of swell The Bretschneider method is the standard method for computing swell characteristics.

35

Explanation 1. The Bretschneider method and the P-N-J method are the two methods for computing swell characteristics. In the Bretschneider method the wave height and period of the swell are inferred from various phases of the significant wave. In the P-N-J method, various phases of swells are obtained by estimating the results of the dispersal speed and dispersal direction of the wave spectrum. The Bretschneider method among these is the simplest, the easiest to use and is taken as the standard method.

36 H0: Unrefracted deep water wave (significant wave) U: Mean wind speed F: Fetch hF: Water depth at the edge of fetch F m: Slope of sea bed g: Acceleration due to gravity t Coefficient of sea bed friction Ks: Shoaling coefficient : Shallow water wave height

uz

ghf/U7 Fig. 2.2.9. Relationship between shallow water wave height, fetch and water depth in cases where water depth is uniform (when / = 0.01) in the Bretschneider method.

However, as sufficiently reliable data for swells are not obtained, more because the accuracy of calculation is lower than the occurrence of waves in the generating area, it is necessary to use the computed values of swell characteristics as a general value, after comparison with actual measured values. 2. Swell characteristics are computed by the Bretschneider method using Fig. 2.2.13. In the figure F is the fetch, D the decay distance, HF and 7> are the wave height and period of the significant wave at the edge of the wind field; Hd, Td are the significant wave at the site. The swell travel time tD is determined, on dividing the decay distance by the deep-water group celerity; CG= g x TdI4k, where TD is the wave period at the total distance D which will be close to the observed values (Fig. 2.2.14): t/> - DICg -

4nD gTp

Units: D in km; TD in sec; tD in hr.

(2.2.34)

Fig. 2.2.10. Relationship between water depth and wind speed (where flm - 5.28), when the sea bed slope is uniform.

Fig. 2.2.11. Relationship between water depth and wind speed (where flm = 10.6) when the sea bed slope is uniform.

38 t

;f

Fig. 2.2.12. Relationship between water depth and wind speed (where flm = 52.8) when the sea bed slope is uniform.

2.3. Transformation of the Wave 2.3.1. General In the design of facilities (installations) the effect of refraction, diffraction, shallow water transformation breaking, reflection and other transformations, as the wave advances are to be considered. Explanation 1. In a water body where the depth of water is more than 1/2 the wavelength and if the wave is not affected by the fraction due to sea bed, it will advance without transformation. However, when the wave reaches a water depth less than 1/2 its length it will gradually be transformed by the influence of the sea bed and the wave celerity. Where the water depth is equal to 1/2 the wavelength that is deep-water area and other areas shallower than this are called shallow water areas. 2. In deep-water area considering the diffraction and reflection of waves because of islands and promontories is necessary. 3. In shallow water areas the effect of shallow water transformation, such as refraction, diffraction, breaking, reflection, etc., will influence and considering them is, therefore, necessary.

39

TtfTp at extremity of D

T period at edge of F (tec)

Fig. 2.2.13. Calculation of swell characteristics.

2.3.2. Shallow water transformation When a wave advances through a shallow water area depending on the change in the water depth it is necessary to consider the shallow water transformation. Explanation 1. The change in wave celerity and wavelength, depending on the change in water depth, can be determined by the formula in (2.2.35), Fig. 2.2.16 and Table 2.2.1. L =— C = tanh---. , 2nh — L q Co L L0 = 1.56 T2 Here h : Water depth; L : Wavelength (m) at water depth h;

(2.2.35)

40 L0 : C : C0 : T :

Wavelength (m) in deep water area; Wave celerity (m/sec) at water depth h; Wave celerity (m/sec) in deep-water area; Period (sec).

30

T d (sec) Fig. 2.2.14. Graph for calculation of travel time for swell.

Fig. 2.2.15. Transformation of the wave in shallow water.

41 2. The change in wave height depending upon the shallow water transformation (water depth alone) can be obtained from the following formula: H - Ks Ho

(2.2.36)

Here Ks : Shoaling coefficient; H : Wave height (m) at water depth h; Ho : Unrefracted deep water wave height (m). The wave height transformation in water, deeper (h/Ho > 4.0) than the graph parameters in Fig. 2.2.16, can be obtained by the small amplitude wave theory formula and by the H/Hq curve shown in Fig. 2.2.16:

Fig. 2.2.16. Wave characteristics in shallow water.

42 (2.2.37)

2I

sinh (4nh/L)

Here H : Wave height (m) at water depth h (m); Ho : Unrefracted deep water wave height (m); Co : Wave celerity (m/sec) in deep water; C : Wave celerity (m/sec) at depth h; Ks : Shoaling coefficient; h : Water depth (m); and L : Wavelength (m) at water depth h. 3. Wave height, breaker height and the transformed wave height after the wave breaks in shallow water area where h/H£ = 4.0 will be calculated as in Fig. 2.3.16 [sic] of Section 2. In the graph, each line shows the maximum height of the breaker. The wave height of a broken wave, depends on the rise in water level because of the broken wave. However, water depth h does not include the water level rise due to the wave setup. 2.3.3. Refraction of waves In shallow water area, where the water depth is less than 1/2 the wavelength, refraction occurs and the resulting transformation of wave direction and height must be considered. Explanation 1. Refraction and Coefficient of Refraction With the incidence of a wave, at an angle to the sea bed contours where the water depth changes from hi to h2 and because of the change in water depth there is a corresponding change in the wave celerity from Cx to C2, the wave refracts at the contour. Because of this, the interval between the wave crests changes from bx to b2, and the distances between wave crests do not change. Hence, infering that the wave energy will not cut across the wave crest is possible. If the loss of energy due to friction of the sea bed or in any manner due to any other reason is disregarded then, according to the law of conservation of energy, comparing the wave height Hx in water depth hx with the wave height H2 in water depth h2 is possible from the formula (2.2.38): (2.2.38)

43 Here c Gl and Cq2 group wave celerities at depths hi and h2y respectively; and bi and b2 interval between crest at water depths hi and h2, respectively. i

Fig. 2.2.17. Diagram explaining refraction and reflection.

.001

.002 .003.005.007 .01

.02 .03 .05 .07 .1

.* .3

.5 .7

1

hlU Fig. 2.2.18. Graph for calculation of parallel depth contours.

Here the ratio Vbjbj shows the effect of refraction and VCGl/CG 2 the effect of change in water using VCGl/CG 2 which is the shoaling coefficient (Section 2.3.2 shallow water transformation). One can show that VCGJCG2 = KSJKS2. Here Kn and Kn are the shoaling coefficient at water depths hi and h2, respectively. Because of the refraction, the distance between wave crests in deep water, changes from bo to b and the ratio of wave heights is called the coefficient of refraction. The coefficient of refraction Kr is represented by the formula (2.2.39): Kr = Vbjb

(2.2.39)

44 2. The Change in Wave Direction due to Refraction can be Obtained from the Refraction Diagram However, to obtain accurate measurement is difficult when the intervals between depth contour are highly unequal because of the complex configuration of the sea bed, the sea bed slope is steeper than 1 / 1 0 , to obtain the change in wave height from a wave crest with a high degree of refraction, and within the breaker zone, and conducting hydraulic model tests are desirable.

a. Method of using circular refraction template i) Obtain Ch C2, C3 for each water depth and also the ratio CJC^i from the wave celerity at point C, and wave celerity for the earlier point C,_i and tabulate. In Table 2.2.5 examples are for T - 12 sec. Table 2.2.5. Table showing wave celerity ratio and wavelength ratio Wave celerity Ci

100 m 80 60 50 40 30 25

C0 = Cx = C2 = C3 = C4 =

II b2 crests the next midcontour. In this manner continue till the wave direction line reaches the breaker zone. b. Method of wave refraction using refraction template i) When the incident wave makes an angle of less than 80° with the normal to the tangent at the contour line. 1. Make a sounding chart to a scale of 1:3000 with depth contours at suitable intervals which include the point at which the refraction occurs and include all the depth contours less than 1 / 2 the deep water wavelength. 2. If the contours are uneven, smoothen them disregarding all minor irregularities; the purpose being to obtain a general chart with depth contours for which these deletions and changes are carried out. 3. Determine the wavelength and direction of approach of the deep water wave. 4. Find the wave celerities Ch C2, C3, ..., etc., corresponding to the depth contours in decreasing order from the deep water area to shallow water area using Table 2.2.1 and simultaneously calculate CyC2) C2 /C3 , C3 /C4 , ..., etc., and tabulate the values. 5. Draw the midcontours between the contours by visual estimate. 6 . Using a transparent celluloid plate make a refraction template to any convenient scale as in Fig. 2.2.21a which can be used on sounding charts of any scale. 7. At the point of intersection, P, of the extended orthogonal of the incident wave OA with the first midcontour, draw a line P'R normal to the line AP'. Place the template superimposing point M of the template (made at 6 ) on P' such that the line MR of the template and P' on the chart coincide.

46 Tangent to the wave orthogonal Depth contour (C - G )

Tangent to the mid-depth contour

Depth contour (C = G ) l

Tangent to the wave orthogonal

^ sino;

p

Fig. 2.2.20. Method of drawing refraction diagrams. ► R/J l.S

0. 9 i.O

2 0 2 53 0

Center of rotation of template

0.5 0.4 0.35' 0.30! *

0.25 02

1 1 0.1

a ia is u iia s ik u a ia ia iiia iia a iiia ife ? iiia i^ iia iH ii^ a iiia a iiiaaiik?aiiB ?i9aaK iai«kiiiii fe sn » im ii9 iiic in a K aa ^ iia ■■ i:a isia a a a iiia a iia cia » a i^ a ia aaaaaaii9a;aaisiiaH;aa^iki«iia S iiiS f ia iiiiH a iii» f e \^ M iiii laia iiftiS P a m siiitM ittiik M i aiiHiaaaaaisaaaisiaikak'ciiM' aBaiaaaaaaaaaBis 0.03) Short period steep waves (0.03 £ H q / L 0 > 0.015) Long period swells (wave steepness H q/ L q ^ 0.015)

Smax = 10

Remark:

H q/ L q

Smax = 25 Smax = 75

is the wave height/wavelength in deep water.

b. Coefficient of diffraction when there is an influence of promontories For instance, as shown in Fig. 2.2.25, when the site A is influenced by the promontory the coefficient of diffraction (KJ) can be obtained by adopting the following procedure. i) Calculate the parameters of the degree of concentration of the wave direction Smax (Table 2.2.7). ii) Obtain the angle 0 between the direction of wave approach and the projected line of obstruction. iii) The energy ratio PE (0) for 0 can be read from Fig. 2.2.24. When the angle of approach 0 ~ 90°, the energy of the incident waves is intercepted by the promontory and does not arrive. iv) The wave height ratio of the waves which reach at point A can be obtained from the square-root of the energy ratio PE (0) for 0. For instance, if 5 nmx = 75 for 0 = 18° from Fig. 6.6.2*, PE (18°) = 0.91, that is, 91% of the total energy of wave reaches points, the wave height ratio will be: Ka = Vfr9T = 0.95. Direction of wave approach

Fig. 2.2.25. Wave diffraction due to a promontory. *As in original. Probably it is 2224 — Editor.

51 3. The diffraction coefficient (for every component of wave) when affected by protrusions can be calculated from diffraction diagrams [Fig. 2.2.29a-g]. 4. When the width of the entrance is up to 1/2 the wavelength of the incoming wave and each wave is perpendicular to the entrance, the coefficient of diffraction should be calculated from the diffraction diagrams [Fig. 2.2.30 a-r]. When the entrance width is greater than 5 wavelengths of the incident wave, the diffraction is calculated in the same manner as diffraction due to a solitary obstruction/projection for both sides separately (Fig. 2.2.26). When the wave approaches at an angle, the respective wave field of waves would be as shown in Fig. 2.2.27. The entrance width must be examined and the appropriate diffraction diagram be adopted for the design width. 5. In the case of islands, for arriving at diffraction coefficients, consider the two end sections as projections, calculate the effect of diffraction at each end and add up the results of both wave crests. For island conditions, when the width is less than 3 wavelengths, the wave heights undergo large changes. 6 . When there are shore breakwaters, dikes, etc., and the sea bed is not even, both diffraction and refraction occur. In this case the transformation of direction characteristics of the wave can be calculated by adopting the following procedure: a) Draw a wave front up to the breakwater or dike; b) From this point to the coast, calculate the diffraction effect, without considering the refraction, for a distance of 3-4 wavelength; and c) Draw refraction curves from the wave crest line from the farthest point on the coast as calculated in (b) and find the wave direction at the required point or in the wave breaking zone.

Breakwater

Breakwater

Lines representing wave crests

Fig. 2.2.26. Case of B > 5L.

Breakwater

^Design entrance width

Fig. 2.2.27. Design entrance width.

52

Lll, ,,,,,,,,,,, ?\,r7r»-.

Wave crest lines

Fig. 2.2.28. Combined diffraction and refraction diagram.

Direction of wave approach

Fig. 2.2.29a. Diffraction diagram for 9q = 90° in case of promontory tip.

53

Fig. 2.2.29b. 0O = 15°. x/Z.

54 x/L

Fig. 2.2.29d. 0O = 45°. x/L

55 x /L

approach

Fig. 2.2.29f. 0O = 165°. x/L 0

5

Fig. 2.2.29g. 0O = 180°.

10

i

x \L Fig. 2.2.30a. Diffraction diagram for entrance width BJL = 0.5.

t

x/L

Fig. 2.2.30b. Entrance width B/L = 0.6.

t

x /L Fig. 2.2.30c. Entrance width BIL - 0.8.

xlL Fig. 2.2.30d. Entrance width BIL - 1.0.

I

c

)

*/*■ Fig. 2.2.30f. Entrance width B/L = 1.4.

t

x/L Fig. 2.2.30g. Entrance width BIL = 1.6. t

x /L

Fig. 2.2.30h. Entrance width BIL = 1.8.

t

x /L Fig. 2.2.30i. Entrance width BJL - 2.0. t

t

Fig. 2.2.301. Entrance width BIL = 2.6.

t

L

t

Fig. 2.2.30p Entrance width B!L = 4.0.

&

i

65 2.3.5. Reflection of waves The effect of reflection of waves from structures or promontories, if occurs within the area o f interest, must be considered. Explanation 1 . Caution must be exercised in designing a structure as there are times when fishing grounds/hatcheries are areas in the sea where environment is created similar to natural habitat of fish, etc., while aquiculture is fish culture in water bodies which can be on shore. 2. In normal cases the reflected waves due to reflection from structures, are found by the formula: Hr = RHi (2.2.39) where HR = Reflected wave height; R = Coefficient of reflection; Hi = Incident wave height. 3. In case of limited length of a structure, at a point away from the reflection surface, only a component of the reflected wave reaches the point and if the reflected wave is small wave height can be calculated using the formula 2.2.40. The reflected wave direction will depend on the direction of wave approach

Hr = RlQHj

(2.2.40)

Here Kd is the coefficient of diffraction when the reflection surface is at the entrance. 2.3.6. Breaking wave height While designing a structure if the water area in the vicinity of the breaking wave becomes the point of focus then, as shown in this section, the characteristics of waves and water levels must be investigated. When the water level is important for design the rise in water level above normal sea level due to tides, storm surges and wave setup must be added to the normal sea level. Explanation

Waves in the breaker zone are influenced by the change in water levels, sea bed friction, turbulence due to waves, etc. The wave height during this interval can be obtained from diagrams [Fig. 2.2.32a-e]. The water level near the point of a breaker zone is obtained in the following manner: 1 . Within the breaker zone the rise in water height, due to the wave, has been determined by Longuet-Higgias and Stewart. Depending on the breaking wave the water level falls on the deep-water or sea side and rises on the shore side.

66

Fig. 2.2.31. Calculation of reflected wave from proposed breakwaters at the entrance. Table 2.2.8. Values of the coefficient of reflection Type of structure Vertical wall (top above still water level) Vertical wall (top below still water level) Stones in slopes (gradient probably 2-3 in 10) Armor blocks in slope Breakwater with vertical face Natural beach

Coefficient 0.7-1.0 0.5-0.7 0.3-0.6 0.3-0.5 0.3-0.8 0.05-0.2

Fig. 2.2.32a. Change in wave height depending on water depth.

67

Fig. 2.2.32b. Change in wave height depending on water depth.

Fig. 2.2.32c. Change in wave height depending on water depth.

2. Considering the height of the structure projections, etc. in the calculations is necessary. 3. The rise in water level because of the wave can be calculated using graphs (Fig. 2.2.33a-e). In the graphs [Fig. 2.2.33a-e]: fj : Rise in water level; i : Average sea bed slope (breaking zone); H'o : Unrefracted deep-water wave height (m); h : Water depth at point of interest below still water level.

Fig. 2.2.32d. Change in wave height depending on water depth.

Fig. 2.2.32e. Change in wave height depending on water depth.

Fig. 2.2.33a. Rise in water level due to breakers.

69

Fig. 2.2.33b. Rise in water level due to breakers.

TT S

When cohesive soil = C-26 log C: value 52-60

W n

Safe bearing capacity qs (kgf/cm2)

W p> wn>ws qa =2.0 When W s> wn 9a =4.0 When

(b)_________________________________________ Compression coefficient Cc Undisturbed soil with low percentage of clods WL - Cc

Cc = 0.09 (Wi = 10)

Kanto loam

Cc = 0.011 (WL = 10)

Alluvial soil from Osaka

Cc ~ 0.01 (WL - 12)

Conventional of soil p = 1 .6 - 1.8 p = 1.3 - 1.6 p < 1.2

f

Property f |.

(c) classification

State of soil Compact soil Friable soil Soil with high organic content

(e)

(d) Property

Permeability of soil k (cm/sec)

Property

Angle of internal friction “ O'” of clay of uniform density

D 10 (cm)

k = C D \0 C : values 50 to 100

Plasticity Ip

Sin 0' = 0.81 - 0.23 logio h

115 2. Table 2.5.3 shows the engineering properties of soil classification according to the standard soil quality classification of Japan. 3. Table 2.5.8 summarizes various soil characteristics according to the standard soil quality classification of Japan. 4. Table 2.5.9 is the classification used in the geologic chart for sea and land. The classification in Table 2.5.10 is also used.

t

10

d

1/im

Colloid

7 .6

3 .8

5//m

1.3

-1 .0

74//m 0.42m m

Fine sand

Clay

-2 .3

2.0m m

Coarse sand

-4 .3

5.0m m

Fine gravel

-6 .2

20mm

Medium gravel

-8 .2

75mm

Coarse gravel Cobble

Silt Sand

Classification of soil

30cm

Boulders

Gravel

Rocky material

Fig. 2.5.2. Classification of soil grains and their nomenclature [3] (Standard Soil Classification of Japan). Note 1. Soil is classified either in accordance with the grain size or in accordance with the grain composition. Note 2. Soil material composed under 74 pm is in the “ fine grain class” , 74 pm to 75 mm in the “ coarse grain class.”

5.4. Mechanical Properties of Soil 5.4.1. General 1. The mechanical properties of soil must be obtained as data for investigating the stabilityf sinkage and changes in the foundations of fishery structures. 2. In the design of fishery structures the major mechanical properties are shear strength and compressibility of the soil. To understand these mechanical properties, the particle size composition of the soil is used and the subsoil is divided into sandy soils and cohesive soils. Explanation The mechanical properties of soil have a direct influence on calculations of bearing capacity, soil pressure, subsidence, etc., of the subsoil of fishery structures and they must be studied with care. As natural soil is generally not uniform, to calculate the mechanical property of the subsoil carrying out comprehensive tests to reach to conclusion is necessary.

- | C oarse soil grain |

C oarse grained class (material abcve 7 4 |im) is over 50%

lR

G ravelly soil | (G) Gravel (material 2 .0 -7 5 mm) within th e coarse grain is over 50%

}

* - S andy soil

Soil grain under 7 5 mm

Fine grain soil

(SJ Sandy class (material 74 p m -2 .0 mm) in the coarse grain class is over 50%

/ C T

C layey soil of fine grain d ass

(G -O )

O rganic soil of fine grain class

(G -V )

Volcanic ash of fine grain class

Silty gravel

(GM )

Silt of fine grain d a s s

Clayey gravel

(G C )

G ranular clayey s d l of fine grain clas

(GO)

O rganic soil of fine grain class

(GV)

Volcanic ash of fine grain class

( G ravel mixed with organic soil

Fine grain class 1 5 -5 0 %

U c 'S l

G ravel mixed with volcanic ash

R egarding classification of gravelly soil, the word “gravel” can be replaced by the word “sand” and by changing symbol G to S lO-2

GM

Silty gravel, gravel 1.92-2.16 mixed with sand and silt

Good

i io-3

SP

Sand or sandy soil: with 1.60-1.92 a poor granular distribution, fine grain content low/none

> 10~3 Good or bad dep­ ending on the density

SM

Silty sand: sand and silt 1.76-2.00 mixed

Good or bad de­ pending on the density

io-3-i50

qa (t/m2)

Requires strengthening

7-25

25—45

> 45

Notes: 1. When the subsoil water is either near or above the bottom of the foundation, the permissible values for maximum settlement is 2 inches (5.1 cm), provided the thickness of the sand layer is wider than the width of the solid foundation. 2. The weight of the structure considered to be uniformly distributed on the foundation. 3. When the depth of the rubble base is less than B/2 or when it is at a place where the subsoil water level is deeper than B/2, the permissible bearing strength has to be increased.

When the clayey soil is subjected to continuous loading, even when the value does not exceed the permissible bearing capacity, settlement cannot be ignored. Table 2.5.14. Permissible bearing capacity of day Consis­ tency of day

N

Very weak

>2

>0.25

Weak

2-4

0.25-0.5 7.1-14.2

Normal

4-8

05-1.0

Hard

8-15

1.0-2.0 285-57

Very hard

15-30

2.0-4.0

Dense

< 30

< 4.0

qu : qd : q^ : qa : q’a :

qds q“ ? 4.5

> 3.2

2.2-45

45-9.0

3.2-65

6.0-12

45-9.0

9.0-18

65-13

37-74

12-24

9.0-18

18-36

13-26

57-114

74-148

24-48

18-36

36-72

26-52

< 114

< 148

< 48

9.2

9.2-18.5 3.0-6.0

14.2-28.5 185-37

Direct compression (kg/cm2); Safe bearing capadty for long continuous foundation (1/m2); Safe bearing capadty for square foundation (t/m2); Long-term permissible bearing capadty (t/m2, F$ = 3); and Short-term permissible bearing capacity (t/m2, F$ = 2).

5.43. Cohesive strength of clayey soil To find the cohesive properties of clayey soil obtained (1) the value of maximum settlement and (2) the changes in the rate of settlement for the load. Explanation 1. As clayey soil has a high compressibility and permeability, slow consolidation by compression takes a long time. Hence, it is necessary to obtain

125 Table 2.5.15. Standard compression test and compression value Individual load stage

Total load stage

Relationship

Settlement vs. time curve

Ratio of voids vs. pore pressure

Cohesion value

Coefficient of compressibility (mv) Coefficient of cohesion (Cv) Coefficient of permeability (&)

Cohesion yield stress (Py) Compression index (Cc)

the maximum settlement and rate of settlement. To understand these carrying out compression tests on undisturbed soil samples taken at the site is necessary. 2. The various cohesion values of clayey soil can be obtained by the standard compression test (JIS A 1217). In the standard compression test a uniform weight is applied and removed every 24 hr on a confined clayey soil sample block, and the cohesion values obtained from this test are as shown in Table 2.5.15. These values are categorized into two types: 1) value obtained at each stage of loading; and 2 ) sum of the values obtained at all the loading stages. 3. The calculation procedure for the maximum value of settlement is indicated in Fig. 2.5.7.

Fig. 2.5.7. Procedure for calculating the limiting values of consolidation.

126

B

Fig. 2.5.8. Dispersal of pressure stress.

The increase in pressure at the center of various compressed layers of soil due to uniformly distributed load can be obtained using Fig. 2.5.8 and the following formula: _ % = ----------------------------------------------- (2-5.16)

1+115 i For loads from a breakwater refer to Fig. 2.5.9 and the following formula: &oz = qo(Ksi+Ks2)

(2.5.17)

Here coefficients Kii and Ks2 are obtained fromFig. 2.5.10.(Obtain a\b\, aj)2 from Fig. 2.5.9individually and convert them to Ksi and Ks2.) 4. Use Fig. 2.5.11 to obtain the rate of settlement. 5. The quantity of settlement cannot be estimated from the results of calculation alone but revising these after observations on settlement of nearby structures, constructions underway, etc. is necessary. The hyperbolic method b,

fll J

bi

T 02

S. Qo m

A > Cma : Coefficient of resistance, coefficient of absolute mass (ref. Table 4.1.2); A : Total area of fish cage obstructing the flow; K : The coefficient of restitution of foundation for the sea bed (in case bed is gravelly, as it is also related to the hardness of the sea bed); its value lies in the range of K = 3,000-5,000 tons/m2. Compute MIL and NIL using formula (4.1.4). Figure 4.1.1. shows the plots. 2. The impact oc when the fishes are released/lowered into the fish cage: In such a case the reaction from the foundation at the time it reaches the sea bed is R = IQ. The cumulative coefficient of restitution Kx can be determined from the cumulative effect of the coefficients of reaction of the individual panels, namely, K2, K3 . . . , etc., from formula (4.1.7): Ki = K-e

(4.1.6) (4.1.7)

— +— +— + . . . Ko Kx K2

In this case cfc is according to formula (4.1.8) o q - L+VU+M L = (o (eg—vv0)— V ' 4g V M = —— (Oa+Cm,wo) gV

(4.1.8)

157

3. Final velocity v at the sea bed: The final velocity v, in free fall on the surface or in the sea is obtained by the following: v, = (--l) ( 4 - 1 -9) CdA \wo / v - v jl-e x p L . . M o g / ^ ± ) I P (4.1.10) [

I

O g /W q + C ma) Vc

J J

In case water depth is greater than 10 m, the final velocity v is given by formula (4.1.9). In this formula vc : Velocity at the bottom end of cage; h : Water depth; A : Total area affected on the sea surface when the fish cages are lowered (total of each member); CD, Cma '■Coefficient of resistance, coefficient of absolute mass, respectively (according to Table 4.1.2).

158 Exp (x) refers to e*. In case a mobile or ship winch is used, in addition to the velocity of fall, the movement of the ship must also be considered and the vector or resultant velocity should be adopted. Always v j> 1.0 m/sec.

J

Tubular

tton

Designa-|

Table 4.1.2. Coefficient of resistance and coefficients of mass

Plate

Rhombic

>. CD

I

it

X

r t

Ha

l

2

5

10

20

40 S

l

CO

i

2

4

5

10

20

oo

CD

0 .6 3

0 .6 8

0 .7 4

0 .8 2

0 .9 0

1 .0

1 .0 5

2 .0

1 .1 2

1 .1 5

1.1 9

1 .2 0

1 .2 9

1 .5 0

2 .0

CM

2 .0

2 .0

At/(tta)

C MA

1 .0

1 .0

1 .0

Area

al

al

al

Volume

na2l/A

abl

na2l /

+ 1 . 0

4

Note: 1) As a rule the values given in the table can be used. But when using a value of C D outside this table reliable data should be used. 2) In case where the members are assembled in a complex manner, a reliable model experiment should be carried out to reduce the undercurrent side Cp.

1.5. Hydrodynamic Force Hydrodynamic force is due to impact of waves and currents. 1. Design Wave The various principles of the wave used in calculations for stability and for the structure of the established fabricated fish cages should be determined on the basis of reliable observation data or on computations based on wave data. a) When the wave observation data are available for a sufficient period for the sea zone under consideration calculate the various principles of the deep sea wave on the basis of the data mentioned in Part 2, Section 2.2, Computation of design wave.

159 b) If in the sea zone under consideration there are completed projects, such as harbors, fishery ports, etc., then the deep sea design wave adopted for these projects should, respectively, apply to these facilities as well. c) Because of the land configuration, if the methods (a) and (b) are inappropriate, then analyze the meteorological data (wind direction, wind velocity, fetch, duration) and use Part 2, Section 2.2.2, Computation of a wave, which considers land formation. On the above basis calculate the deep-sea wave for the sea zone under consideration. d) When the characteristics of the deep sea design wave have been determined, then compute the wave height transformation (changes in the wave direction and wave height) due to propagation caused by refraction, diffraction, shallow water effects, etc., of the wave till it reaches the project site in the sea zone using Part 2, Section 2.3, Transformation of the wave. Use the most critical wave in the design wave spectrum. e) The design wave is based on the significant wave. 2. Design Current Velocity The design current velocity can be obtained using the method in Part 2, Section 3.2. 3. Computation of Wave force If the wave depth h, at which the fish cage is installed is deeper than 1/2L (L = wave length), then the wave force must be considered. i) Nonbreaking zone The maximum wave force F of the wave can be obtained in the following manner: u = um sinO (4.1.11)

(4.1.12)

when

(4.1.1.3)

when Here Cm, Cd : Coefficient of apparent mass, coefficient of resistance force using values of Table 4.1.2;

160 A : Total affected area of the plane perpendicular to the direction of wave flow (sum total of each member); w>0 : Unit volume of sea water; h : Water depth; D : Height of fish cage; H, L, T : Weight height, wave length and wave period at the place of installation of cages. In the case of a large type fish cage which has a complex shape if the current velocity acting on it is taken as the same as the current on the upper section there can be a large difference. Therefore reliable hydraulic model experiments should be carried out. Model experiments for lower wave movement (irregular flow) should be used to obtain the coefficient of resistance CD and the coefficient of apparent mass CM (CMA + 1). But with the coefficient of resistance obtained by model experiments for uniform flow in the lower section, follow the next procedure to calculate the coefficient of virtual mass CM. With At as the total projected area of the surfaces in the direction of flow of uniform flow, obtain CD experimentally. The ratio of CD, the mean average coefficient of resistance of the members added up and CD, obtained by the experiments is Cd/ Cd = l/rD in this case Cm, the coefficient of apparent mass is CM = — = rM

Cm

(4.1.14)

n

here Cm is the total CM of the individual members. ii) Breaker zone In case of submerged fish cages established within the wave breaker zones the total wave force on them is calculated by the following formula F = 0.31 CdAwqH

(4.1.15)

the point at which F acts is the center of the diagram A. Here H, h : Breaker wave height and breaker water depth at the place the fish cages are installed; CD : Coefficient of effective area of resistance (value according to Table 4.1.2). Here the coefficient 0.31 is obtained by considering the velocity of advancement of the breaker wave as a steep wave. The propagation velocity is determined by model test and used in the formula to obtain the force acting on an object in the center of the flow.

161 4. Force of the Currents The current velocity uz acts on the upper portion of the installed fish cages. The force due to wave currents are calculated by the following formula: F = CdA wo Yg

which is considered as the maximum value of F is shown in Fig. 4.1.2. If this is used then: F = Cd A

(«2 + 0 2

can be obtained.

g

2

(4.1.21)

162

ob Fig. 4.1.2. The value of Q> when wave and ocean currents are mixed.

1.6. Strength of Members The bending moment, compression, tensile and shear stresses caused in the members of the fish cage structure are calculated for the design external force mentioned in sections 1.3-1.5, acting upon the cage. The intensity of stresses caused by these forces in the member must be below the safe permissible stresses in the materials. The bending moment, compression and tensile and shear stresses must be calculated for each fish cage structure. In areas where stress is concentrated, such as corners of angles a gusset plate can be inserted for extra strength. Explanation The stress on members is to be computed for each fish cage. But in the case of square cages use the values shown in Fig. 4.1.3 (in the case of flats) and Fig. 4.1.4 (in the case of angles) and carry out calculations for the member: q = b G-a = k o G a

(4.1.22)

163 Here a : cross section area of fish cage structural member; aG, aG, k : values according to formulas (4.1.3) and (4.1.8). The procedure for computing sizes of reinforced concrete members is as follows: 1. Calculate the bending and tensile and compressive stresses in the main beam; 2. Check for shear force; 3. If shear stress is beyond limits use extra stirrups; 4. When shear stress is within permissible limits only nominal stirrups for assembling the reinforcement are sufficient; 5. For the force caused due to impact at the bottom, on the fish cage the resistance intensity in the concrete should be taken (oct = 1/10 oca, aca the safe permissible stress in concrete for a short period);

a) Bending moment diagram

b) Axial force diagram

c) Shear force diagram

Fig. 4.1.3.

ZiqS

tj2 a) Bending moment diagram

b) Axial force diagram Fig. 4.1.4.

c) Shear force diagram

164 6. In case of factory produced precast concrete main beams, which are of a suitable strength for the structure, the highest value of 20 mm cover should be provided as a minimum. Keep cover above 25 mm for those made at the site. These standards can be followed for special construction till JIS are prepared for the same. 1.7. Stability of Fish Cages Fish cages can overturn or slip by the action of waves and currents on them. Explanation The wave force and the tidal force F can be obtained either from the formulas (4.1.13)-(4.1.16) or (4.1.17)-(4.1.21). The following conditions are to be fulfilled to ensure stability against force F. 1) Conditions for Preventing Slippage v

= V f K i - W o g) > 1 ,

(4123)

F Here W : Weight of empty fish cage; oG; vv0 : Unit weight of fish cage material and sea-water, respectively. Sps : Safety factor for stability against slipping; p : For gravel, the coefficient of friction between the fish cage and the sea-floor p. = 0.6. Passive soil pressure of the sand can be considered when the legs of the cage are buried in the sandy sea bed. 2) Conditions for Preventing Overturning Sps = F

. Jv_ ^ j 2 lA

(4.1.24)

Here lA : Vertical distance from sea bed to the center of pressure diagram or line of total force; ly : Horizontal distance to the centroid of the cage from the toe of the cage. Carrying out a representative investigation is necessary when the sealevel slopes, using the various values, by resolving and analysis in the direction of the normal and the tangent of the forces of gravity and buoyancy acting on the base, in the formulas (4.1.23) and (4.1.24). When the fish cage is placed on gravel, sand, soil or mud, care should be taken to ensure that there is no loss in its function due to erosion, burial,

165 subsidence, etc. Particular care should be taken against subsidence due to pressure and burial in sandy or gravelly coast. Sample Computation As shown in figure a square-type fish cage is lowered to a depth of 40 m. The force of impact when it touches the sea bed is given by the weight calculated at still-water level. This can be obtained for 2-layer and 3-layer stacks as well. However, the coefficient of restitution of the sea bed is K = 5000 tons/m2 and elastic constant of the fish cage, under the conditions shown in the figure is, Ko = 600 tons/m.

Fig. a, Square-type fish cage

Explanation Actual volume V = Actual volume of fish cage-(internal volume + window volume) + Volume of chamber; = 1.53 - | l . l 3 + | l .l 2 -

x 4 j x 0.2 x 6 | +

x -i- x 8

= 0.617 m3. Area obstructing the flow, perpendicular to the face = area within the window + opposite side area; A = 1.52- | l . l 2- ^ x 2 j

J+ 0.2x 1.1 x 4

.94 m2. Area obstructing the flow at 45° to the face of the cage; A = [ j 1.52- | l . l 2- — x 4 jj cos 45° x 2 + 0.2 x 1.1 x cos 45°x2

166 +[(1.5 cos 45°x 2 -0 .2 cos 45°x4)x0.2x2 + 0.2 cos 4 5 ° x 2 x l.l] = 2.74 m2. a) Obtain drop in speed At the time the cage reaches the surface of water. Obtain vc from formula (4.1.9) Obtain the coefficient of resistance CD, as the form of the parts of the fish cage members are square in shape, from Fig. 4.1.2 use CD = 2.0: ,4

2 x 9.8 x 0.617 I2A5 -1 2 x 1.94 1.03 = 2.07 m/sec

Obtain v from formula (4.1.10). From Fig. 4.1.2, the coefficient of absolute mass Cam is Cam = 1 v = 2.07 x

2x9.8x40x — -1 V _________ 1 1-03 )\ 2.45 + 1 : 2.072 1.03

1 - exp

1/2

= 2.07 m/sec If the water depth is more than 10 m then with v = vc the calculations of formula (4.1.9) alone are sufficient when it hits the water surface at an angle. From formula (4.1.9) '2 x 9.8 x 0.617 2.05 x 2.74 W V1.03 = 1.74 m/sec b) Obtain q? the computed weight at still water level, at the time of impact when it reaches the bottom obtain e from formula (4.1.4.): K = 500 kg/cm2 = 5000 t/m2 When it hits the surface perpendicular to surface, from formula (4.1.4): L=

9.8 x 5000 = 2.57 x 104 3 x 1.03 x 0.617

M = 9.8 x = 6.77 _ / 2.45 N

1 1.03

2.45 -1 1.03 + 1.01

-

2.0 x 1.94 x 2.072 4 x 0.617 = 7.24

167 Substitute these values in formula (4.1.5) 8l = ( — — — ) 3 = 6.56 x 10- 2 \2.57 x 104/ 2.57 x 104 x er3 - 6.77 x e, - 7.24 er + 1 = e, ---------------- i----------------- i---3 x 2.57 x 104 x er2 - 6.77 r = 1 8 2 = 6.69 x 10- 2 r = 2 8 2 = 6.69 x 1 0 ~ 2 = 8 If substituted in formula (4.1.3) then A

o G=

0.617

When it approaches at an angle From formula (4.1.4) L _ — 9.8 x 5000— _ 2 5? x 1 Q 4 3 x 1.03 x 0.617 no , 2.45 .\ 2.0x2.74 . M = 9.8 x ----- 1 x 1.742 1.03 / 4 x 0.617 = 6.79

N=( —

\ 1.03 = 5.11

+l.o) x — /

2

Substitute in formula (4.1.5) 5.11 U ex = ' *3 2.57 x 104j = 5.84 x 10-2 2.57 x 104 x er3 - 6.79 er - 5.11 E , + 1 " Er 3 x 2.57 x 104 x e, 2 - 6.79 r = 1 e2 = 5.99 x 10“ 2 r = 2 8 3 = 5.99 x 10-2 = 8 From formula (4.1.3) . 5000x^2 0.617 c) In case of stacking the cages in 2 layers From the above calculation of the reaction/?, in case of hitting at the surface of water can be found from formula (4.1.6) Ki = 5000 x 0.0669 = 335 ton/m

168 K2 = 6000 kg/cm = 600 ton/m From formula (4.1.7) Ki =

_1_

i

_1_

= 215 ton/m

600 + 335 Having obtained KL substitute in formula (4.1.8) 2 0 x 1 94 x 1 03 x 2 07^ L = (2.45 - 1.03) = 0.712 4 x 9.8 x 0.617 215 x 2 072 M= X (2.45 + 1.0 X 1.03) = 530.2 9.8x0.617 v ' oG= 0.712 + V0.7122 + 530.2 = 23.7 ton/m3 For the falling fish cage, the weight distribution is 23.7 tons/m3 and the falling fish cage experiences a concentrated load of R = 23.7 x 0.617 = 14.6 ton For (a) to (d) points, the calculations are the same when it hits at an angle. d) In the case of stacking of fish cages in 3 layers use formula (4.1.7) Kl = --------- ---------- = 158

2_+_L +2_ 600

335

600

Substituting values in formula (4.1.8) 2 0 x 2 74 x 1 03 x 1 74^ L = (2.45 - 1.03) = 0.713 v ' 4 x 9.8 x 0.617 M is M = 158 x 1/742 x (2 . 4 5 + 1.0 x 1.03) = 275.3 9.8x0.617 v } 6 g=0.713 + V0.7132 + 275.3 = 17.3 ton/m3 from formula (4.1.8). Example (Computation of maximum hydraulic force F acting on the fish cage) To obtain the wave force acting on the upper level of the fish cages in the case of 2 layered stacks of square fish cages shown in the figure below: Assume at the site of cage the water depth h = 40 m, wave height H = 5 m,

169 wave length L = 98.61 m, wave period T = 9.0 sec. Tidal current velocity 2 knots (= 1.0 m/sec). Keep the size of the fish cage same as aforementioned. When V = 0.617 m3 the flow is at an angle to the face of the fish cage A = 1.94 m2. Obtain the velocity of current on the uppermost section of the upper layer of the fish cages. From formula (4.1.11) 2x3.14x3 cosh 3.14 x 5.0 98.61 8F“ X 2 x 3.14 x 40 sinh 98.61 = 0.315 m/sec Uq = 1.0 m/sec —

From formula (4.1.12) Fd = 2.0 x 1.94 x 1.03 x (0.315)2 = 0 02Q2 2x9.8 x 0.617 x 1.03 x 0.315 = 0.016 Fm=2 x 3.14 x 1.0 9.8 x 8.0 1.0

= 3.17 0.315 0.016 = 0.396 P= 2 x 0.0202

a =

>t

r•»jp|oioioi T«/■>>>,f Fig. a.

Obtain S (= sin 0) from formula (4.1.18) S* + 2 x 3.17 x & +(3.172+ 0.3962- 1) S2- 2 x 3.17 x S - (3.17)2= 0

170 The solution is obtained from formula (4.1.20) 51 = 1 s _ 5 Si4 + 6.34S13 + 9.21S12- 6 .3 4 S i- 10.05 2 1 45j3 + 19.02S!2 + 18.42Sj - 6.34 52 = 0.995 = S Similarly If = 0, then 5 = - 0.984; when S = 0.995, C = ± 0.100; and when S = - 0.984, C = ± 0.178. To substitute values in first expression of the 4 solutions of formula (4.1.19) (S = 0.995, C = - 0.100); and (S = - 0.984, C = 0.178) then obtain the root for substituting the values in the formula No. 2 expression of formula (4.1.19): Substitutes = 0.995, C = - 0.100, 1 - 2 x (0.995)2 - 3.17 x (0.995) + 0.396 x ( - 0.100) = - 4.17 < 0 Substitutes = - 0.984, C = 0.178, 1 - 2 x (0.984)2 - 3.17 x (-0.984) + 0.396 x 0.178 = 2.25 > 0 Hence sin0 = 0.995 cosO = - 0.100 is the phase which has the maximum fluid force. If the maximum force F of the flow working on the fish cage is obtained by substituting in formula (4.1.17): F = 0.0202 x (0.995 + 3.17)2 - 0.016 x ( - 0.100) = 0.352 ton/m 1.8.

Floating Fish Cage

1.8.1. Objective and structure The relevant mechanical data of the structural design of the floating fish cage within the middle and upper layer of the sea zone are discussed here. Explanation The structural design should be prepared keeping in mind the following: 1. The floating fish cage is made of a single section and the fish cage members and the fish cage are made up of the floating units (main fish cage, subsidiary members), rope, anchor and the connecting section. The deterioration of the material and reduction in the cross-section, as a result of friction on

171 the various members, caused by all the external forces acting on these at the time of construction and occurring after it is placed, must be considered. 2. The buoyancy should be such that the upper section is supported at the fixed height as there will be no slackness in the anchor rope because of the hydraulic force of the current and wave. 3. If there is any slackness in the anchor rope then at the following stretch of the anchor rope a great shock occurs and causes damage to the connecting section or the anchor rope. To prevent this the required buoyancy acting on the upper section should be greater than the total downward vertical force. To support the upper portion of the floating fish cage at a certain point h above the sea bed, the required buoyancy N is h Fh + \~ F ih N>: + Fv / Vl - (h/l)2 V

(4.1.25) K J

Here I : length of anchor rope; Fh, Fv : horizontal and vertical components of the hydraulic force, caused only by the currents acting on the upper part of the floating section; Fm : horizontal force distribution caused by the hydraulic force of the current acting on the anchor rope only; and the excess buoyancy N, so that there is no slackness in the anchor rope is N > (Fw)mJ c oscp

(4.1.26)

Here the value of (F^)max and cp are according to formula (4.1.30) and formula (4.1.28), respectively. The required buoyancy is determined by formula (4.1.25) or formula (4.1.26) and the greater value of the two is taken. 4. The structure of the connecting section should be such that failure does not occur because of torsion and friction and only such material which does not deteriorate because of repeated loads should be used. 5. The anchor must be stable against action of all external forces where the floating cage is established. 6. The characteristic period of oscillation of the floating section must be the same as that of wave period. When the floating portion is freely oscillating in still water that period of oscillation should be assumed to be the character of the period (referred to below as characteristic period) of the floating fish cage. Under periodic external forces (wave force) similar to the characteristic period the floating section oscillates together and as the damage is caused by a great force acting on the anchor rope, the characteristic period must be the same as the wave period.

172 C m

-

05

For To the set period of the floating fish cage, with the force acting on the center of gravity of the float and anchor rope being considered as uniform and taking the forces to be converging at a point on the anchor rope, the oscillation is taking place only because of the anchor rope. In this case, the characteristic period T0 of the floating fish cage is given by formula (4.1.27): T0 > 2x { i . V (Cm +° g/ w2) 1 » g ' (l-oc/wo) Qg =

here

N

1

w0 VVqVq wo : unit weight of water; oG : apparent weight of total fishcage; Vq : apparent volume of fish cage.

(4.1.27) K '

173 Cma = 10

Fig. 4.1.5(b). Characteristic period of floating fish cage.

In general, the water depth at which a floating fish cage should be placed in a sea zone is 100-150 m or deeper and the cage itself should be placed within 30 m from surface. Figures 4.1.5a and 4.1.5b show the ratio o/p for the required buoyancy and the characteristic period for different anchor lengths obtained from formula (4.1.27). Moreover, in general, as in the open sea in the case of a characteristic period below To = 20 sec, there is a possibility of resonance and the design parameters to prevent this are shown in thick curved lines in the diagram of curves. 1.8.2. Design external force Investigation of all the external forces acting on the fish cage both at the time of construction and after its establishment is necessary to identify and evaluate the critical external force, but here only the external forces acting after establishment of the fish cage will be discussed 1. The virtual weight of the total fish cage oG is arrived at, considering the weight of the attached organisms, with the following formula: oG = (W+ WB)/V

174 Here W : Total weight of members, including anchor rope; WB : Weight of attached organisms; V0 : Apparent total volume of fish cage. 2. The hydraulic force is the force caused by currents and buoyancy. The calculation of the hydraulic forces caused by the current due to the flow is considered on the increased area of the member's cross section and the excess load caused due to the attached organisms. In order that the fish cage members do not resonate with the waves, the members are to be fixed at points of their flotation. The calculation considers the reduction in weight of the floating body caused by buoyancy. Explanation 1. The weight of the attached organism will differ depending on the species of the organism, the materials used for the floating (nets, buoys, rope), the sea zone in which it is placed and the depth at which it is placed. In general, as attached organisms, purple seaweed in the northern sea zone, and44jujitsubo, ’’ bekko seaweed in the southern sea zone of Japan are excellent. In relation to the water depth, there are differences depending on the region and on the material used for the floating fish cage, in the case of buoys, rings, etc., organisms adhere up to a depth of 50-60 m but with a net or rope they do not adhere at depths deeper than 40 m [5]. While actual measurement of the quantum of attached organisms is desirable in order to determine the weight of organisms, their weight can be calculated taking a value of density as approximately 8 kg/cm2 under submerged conditions (thickness of adhesion 0.07 m, specific gravity 1.4) [5]. 2. The buoyancy is fixed in relation to the vertical forces like dead weight of cage, weight of the various adherent organisms and the tension of the anchor rope for the water depth. 3. When the free oscillation period of the floating structure is not greater than that of the wave the angle of slope cp of the floating fish cage can be calculated by the following: tp = tan-1 (Fo/N) (4.1.28) F0 = ^ (2 CDiAj) u20 2g N = (wo-oG) V Here N : Required buoyancy; oG, vv0 : Weight per unit volume of floating fish cage, weight per unit volume of sea water;

175 A, : The area of the members of the floating fish cage which obstructs the flow; u0 : Velocity of tidal current. 4. When there is no sympathetic resonance from the floating fish cage in response to the waves acting on the various members and to the force of the current the maximum horizontal force is obtained by following the measures in Section 1.5 of this part. The maximum vertical force is created only by the wave and the same is discussed below. When the anchor rope is at an angle only due to hydraulic forces of the current acting on the floating fish cage and Fw is the hydraulic force in the direction of the anchor rope caused by the wave and, as the water depth at which the cage is placed increases, the maximum water particle, velocity of the deepsea wave in the direction of the anchor rope is vm if z is the measured water depth at which the floating fish cage hangs from the sea surface: T Fd = CoA ^ L vm2 2g Fm = CMV ^

(4.1.29)

vm gT

The maximum value of the wave forces (FV)max and the minimum value of (Fw)min are obtained from formula (4.1.30) when Fm > 2FD

(4.1.30)

1.8.3. Anchor rope tension The maximum tension in the anchor rope is due to currents, waves and additional buoyancy. Explanation The maximum tension in the anchor rope is obtained from formula (4.1.31) by taking the sum of equilibrium force of the flow, required buoyancy obtained from formula (4.1.28) and the change of tension in the direction of the anchor rope obtained from formulas (4.1.30) and (4.1.31):

176 Tm

= N /COS Cp + (i*V)max

(4.1.31)

N

Fig. 4.1.6a. Diagram of forces acting on a floating Fish cage. T m c o s 4 = 150m2 C = 0 .5 3

Fig. 43.12. Effective flow cross section area and sea water exchange quantities

bay entrance and the new bay entrance are added together and if the optimum bay entrance cross section of effective flow CA is ^'/t, = 0.95, then CA = 130 m2 from Fig. 4.3.12. However, the new water channel surface area A„ is obtained from the following formula: ^ _ CA-CqAo _ 130 m2-40 m2 _ 15Q m2 Cn 0.6 In this way, An = 150 m2 and, maintaining the water channel width at 50 m is desirable. The flow quantity of the new water channel will be obtained from the following formula: Qn =

Q = O ^ lS O m 2 x 2 x

CA

106 = j 3 9 x 10e m 3

130 m2

per unit area. The mean velocity U„ at the maximum cross section is given by formulas (4.3.10) and (4.3.11): _ 2Q„ = _ 0.56 m/sec U.

REFERENCES 1. Noboru Nakamura, E. Hakuseki and H. Saraki. 1966. Kaisui koryu ni

198

2. 3. 4.

5.

Kansuru kenkyu (Research on sea water exchange). Nogyo doboku shikenji hokoku, No. 4. Noboru Nakamura and S. Hagino. 1976. Kaisui koryu ni kansuru kenkyu (Research on sea water exchange). Dai 23 kaigan kogaku koen kai ronbunshu. Hiromi Nanshin. 1968. Ura no nai wan no kaisui koryu (Sea water exchange in a tidal inlet). Suisan doboku, Dai 5 kan, 1 go (Maritime Engineering Works, Vol. 5, No. 1). Yoshio Tohara. 1966. Chikutei hoshiki ni yoru wan no ichibu shimikiri to kaisui koryu ni tsuite (Regarding closing a section of a bay and sea water exchange by the embankment formula). Suisan Doboku, Dai 2 kan, 2 go (Maritime Engineering Works, Vol. 2, No. 2). Noboru Nakamura. 1979. Suisan doboku gaku (Study of Maritime Engineering Works). Kogyo jiji tsushinsha (Current Engineering Affairs Publishing Co.).

CHAPTER 4

USE OF TIDAL CURRENTS FOR SEA WATER EXCHANGE IN A HATCHERY

4.1. Objective Essential features for improving sea water flow and exchange using tidal current for continuous water exchange in a hatchery. Explanation A tidal continuous current water exchange in a hatchery, here refers to a place which has more than two entrance/exit points and besides a very short period when the flow in reversing, the flow is uniformly one way into the hatchery and out of the other exit. When constructing a new hatchery with structures such as, a breakwater, it is preferable to build one of this type. In this chapter, the procedure for obtaining the sea water exchange and flow in such a hatchery will be determined. 4.2. Optimum Parameters In a hatchery where the sea water flows

in from one side and flows out of the other, the maximum water level difference within and outside the bay is very

small. Explanation The calculation for a continuous water exchange type hatchery which has two openings is normally carried out by an analysis of irregular flow. However, when the water level difference between the inside and outside the bay is sufficiently small in relation to £, the open sea ebb and flood difference then the rate of exchange of the inside-outside water level differences is recorded as same and the calculation of the sea-water exchange is carried out as irregular flow in a channel for each hour [1, 2]. The above appropriate conditions are given by the following formula: IS \2 t _

200 Here S : Area of water surface in the hatchery; A : Area of cross section of flow of water inlet; C : Coefficient of discharge; g : Acceleration due to gravity; T : Tide period; Z, : Open sea tide range. As a rule when the area under consideration is a wide sea zone or the coastline or sea level formation is complicated then mathematical or hydraulic model experiments should be resorted to. 4.3. Sea Water Exchange Flows The sea water exchange flows should be explained by an equation of motion for each exchange inlet and by a differential equation for the total bay area. Explanation If the conditions in 4.2 appropriate parameters are fulfilled then the mean water level time changes within the hatcheries will be the same as in the open sea. The result will be the differential equation to fulfil the internal water level and the movement equation for each exchange inlet will be as follows: (4.4.2) qi = CAi V2g | h-h' | Here h, h' (Fw)max) When (2(Fj))max < (F^max)

(4.14.25)

345 (Fd)max = w0CjJCFHKd (FmU x = w ^.

"---------

^□DDZZfca^ Fig. 4.14.17. Method for four anchors.

2. have:

As shown in Fig. 4.14.17 when there are four anchors on the raft, we T _ 1 n-R-La ^ 2 VL?~/i2

a CQS q

(4.14.44)

Here a : The angle formed by the direction of the anchor rope with the side of the raft (ref. Fig. 4.14.17). 3) Anchor block and size of anchor Obtain after referring to Part 4, Section 13.5, Floating breakwater. REFERENCES 1. Noboru Nakamura. 1976. Uyoshoku shisetsn no sekkei ho, FAO suisan zosho kokusai kaigi ronbunshu (1) [Design methods of floating cultivation facilities. Papers of the FAO International Conference on Development of Marine Products (1)]. Suisan cho (Department of Marine Produces). 2. R. Miyazaki, et al. 1964. Kochi no ryutai teiko ni kansuru kenkyu (II) [Research on current resistance of cord nets (II)]. Joum. Tokyo Univ. Fish, Vol. 50, No. 2. 3. T. Taniwara, et al. Utai gyosho ni sayo suru haryoku ni tsuite (Regarding wave force on floating fish cages). Showa 50 nen nogyo doboku gakkai koen yoshi (Collection of Lectures of the Agricultural Civil Engineering Society Meeting in 1976). 4. Noboru Nakamura. 1971. Saibai gyogyo ni okeru suisan doboku geijutsu (Maritime Engineering Technology for Fish Cultivation). Kaiyo kaihatsu sentaa shuppan kyoku (Ocean Development Center Publishing Division).

358 5. Z. Ishida. 1975. Kochi ken ni okeru okiai hamachi yoshoku shisetsu no shiken ni tsuite (On experimental tests on offshore yellow tail cultivation facilities in kochi Prefecture). Suisan doboku (Maritime Engineering). Vol. 12, No. 1 (Consecutive volumes No. 12). December. 6. Noboru Nakamura, et al. 1976. Keiryu uko no shogeki ryoku enwa ni kansuru kenkyu (1) [Research on import reduction for floating anchors (1)]. Dai 23 kai kaigan kogaku koenkai ronbunshu (Collection of Research Papers of the 23rd Coastal Engineering Lecture Society). 7. O. Sato. 1973. Zoyoshoku shisetsu no setchi ni kansuru jakkan no mondai ten (Certain problems in establishing cultivation facilities). Suisan doboku (Maritime Engineering). Vol. 9, No. 2. 8. Y. Tohara, et al. 1974. Yumei kai nori gyojo ochushin to shita asai kai zoyoshoku gyojo no suiri ni tsuite (Regarding the hydrodynamics of shallow water fish cultivation with reference to the Laver fish grounds in the Yumei Sea). Report of Fishery Research Lab., Kyushu University, No. 2. 9. K. Fukui, et al. 1963. Teibo no tsunami taisako ni kansuru suiri gaku te ki kenkyu (Hydrographic Research for Measures to Protect Breakwaters from Tsunami). Nogyo doboku shiken jo hokoku (Report of Aquaculture Engineering Research Station). Dai 1 go (No. 1). 10. Y. Aida. Kozobutsu ni hataraku namiryoku (Wave force acting on structures). 1968 nendo suiko gaku ni kansuru ka ki kenshukai kogishu, 68-10 (Collection of Articles, Summer Research Workshop 1968 on Maritime Engineering 68-10). Society of Civil Construction. 11. Hiroshima ken nochi keizaibu suisanka (Marine Department, Agricultural Economics Division, Hiroshima Prefecture). Kaki yoshokuho (Methods for oyster cultivation). Kaki yoshoku shireezu I (Oyster Cultivation Series I). 1966. 12. Noboru Nakamura, 1976. Uyoshoku shisetsu no sekkeiho, FAO suisan zoyoshoku kaigi ronbunshu (I) [Design methods of floating cultiva­ tion facilities. Papers of the FAO International Conference on Develop­ ment of Marine Products (I)]. Suisan cho (Department of Marine Produces). 13. Noboru Nakamura, et al. 1977. Yoshoku kada no sekkei gairyoku ni kansuru kenkyu (Research on the external forces acting on a cultivation raft). Dai 24 kai kaigan kogaku koenkai ronbunshu (Collection of Papers of No. 24 Coastal Engineering Lecture Society). 14. Doboku gakkai hen (Society of Civil Engineering edited). Doboku kogaku handobukku (Handbook of Civil Engineering). 1974. 15. Gyowan kyokai hen (Cooperative Society of Fishing Harbors edited). Gyowan kozobutsu hyojun sekkei ho (Standard Design Rules for Fishery Harbor Construction). (1979 kaiteiban) (1979 Revised edition).

16. Nihon kowan kyokai (Japan Association of Ports and Harbors). Kowan kozobutsu sekkei hyojun (Standard Designs for Port and Harbor Construction). Dai 13 sho (Chapter 13). Showa 45 nen 4 gatsu (April, 1971). 17. T. Miyamoto. Gyokai gyohogaku (Study of Shellfish Culture). Kimbara shuppan kabushiki gaisha (Kimbara Publishing Co. Ltd.).

CHAPTER 15

IMPROVEMENT OF ESTUARINE AREA

15.1. Objective An estuarine area is a rich water zone which supports important fish moving up and down the sea and, hence, the closing of the river mouth can lead to great damage. Measures to prevent closing of the river mouth will be discussed. Explanation For fish, such as, salmon, trout, sweetfish which have the habit of moving upstream of the streamy water zones any obstructions upstream and downstream of river mouth can be very damaging for their life support. To ensure increase in the growth of these fish types, planning for the maintenance of the river mouth is necessary. Here various methods for maintaining river mouths will be discussed. 15.2. Mechanism of River Mouth Closure The gorge section of the river mouth is governed by the quantum of tidal flow in the river and the quantum of sand brought into the river mouth by waves and the river itself The section decreases or increases in size depending on the quantum of sand brought by the waves and the current of tidal flow. If the strength of ebb flow is weak then the sand accumulates at the mouth and closes the river mouth. On the other hand if the ebb current is strong the current flushes away the sand into the sea and the mouth section increases in area. Explanation 1. Variation in Cross Section of River Mouth The mechanism of closure of river mouth has been investigated and found to be governed by the quantity of sand brought in by the waves and the strength of river current to flush the sand out. If the river current is strong then the river mouth cross section increases in area, and the converse is true if the

361

Fig. 4.15.1. Shape of accumulated sand in river mouth.

current is weak. If the wave action is strong it brings up lot of sand and dumps it near the mouth where the waves are met by river current and thereby reduces the cross section of river. Thus, because of the stronger wave action and the consequent littoral drift, the sand spit on the downdrift side builds up and the river mouth makes its way by shifting updrift side from where the wave action is less. Finally it reaches a stage where the current is too weak even to make its way through because of losses of energy in negotiating the curves and meandering and the mouth gets completely closed. When the flow through the river is small, as shown in Fig. 4.15.1, the river bed takes a form almost the same as the front section of the bay during heavy wave action. The height of the sand bar/spit can reach the height of the water level at full tide. If the ebb tide discharge also decreases, the mouth gets completely choked in case the wave action is high. Total closure of the river mouth occurs if wind­ blown sand from the seaside, at low tide, adds to the sand spit formation. With the closure of the mouth the water level of the river rises when there is flow in the river, finally breaking through the sand spit and only then will the mouth open out. Besides, the formation of spit in the direction of the littoral drift takes place and the mouth migrates updrift. However, when the currents are too weak the mouth closes, and with the rise in water level at the river mouth the latter opens through the spit. As shown in Fig. 4.15.2, littoral drift will prevail in the direction of incidence of the wave. A sand bar will develop on the downdrift side of the river mouth because of the sweeping current. In this situation, migration of the mouth will set in. If the river, as shown in Fig. 4.15.5, has large-scale migration, the water level will rise at the beginning of the migration section. As a result, the rate of flow at the river mouth will reduce, making ciosure possible. The river mouth will once again return to its original state because of the prevailing current in the sand bar. 2. Limiting Velocities for Erosion The movement of sand caused by the current arises because of friction (shear) and viscosity of water at the bottom. The sand on the river bed does

362

Direction of prevailing wave

4 Movement of littoral sand

Fig. 4.15.2. Wave direction and development of sand spit

—

— —-

Migration of mouth

------------------- River mouth when water is discharged

Fig. 4.15.3. Development of sand spit and opening of river mouth when water is discharged.

not move when the current is weak, but on reaching the limiting velocities for erosion for the corresponding grain size, movement begins and, with increase in velocity the sand is moved up accompanied by a rapid increase in the rate of movement. As agitation of the water increases, the sand becomes suspended in water and evenly distributed over the water surface giving rise to muddy water. Du Bays was the first to study the limiting velocities for erosion. At present, many researchers are studying this problem. Their results are shown in Fig. 4.15.4. In the figure, the abscissa represents the ratio of the squares of the limiting velocities for erosion and the particle falling velocities and the ordinate shows, in a unit time and unit width the quantity of sand scoured qB which passes at eroding velocity u, and sand grain diameter d. The

363

0.3 4

6 8 1

2

3

u \ l { i ~ \ ) 9d)

4

6

8

10

10

Fig. 4.15.4. Comparison of the relationship of eroding velocities of sand.

density of the sand and water is a and p respectively, and g is the acceleration due to gravity. The relationships in the figure are for obtaining the eroding velocities of sand in the river and when the supply of sand is from upstream the sand bar/spit at the river mouth gets opened by the prevailing current and this process can be obtained from formula (4.15.1): q„ . K

( 4 .1 M

(r‘):

*

MKS units are used (m, kg, sec); qB : Sweeping current rate in unit width; K : Experimental constant (= 1.2); g : 9.8 m/sec2,

)

364 R : Hydraulic radius (= cross section of flowing water/length of a side, water depth in shallow river mouth); / : Gradient of flowing water (gradient of river bed which is affected by limiting velocities of downstream); o : Specific gravity of sand ('= 2.65); p : Specific gravity of water (= 1.0); d : Grain diameter of sand. 3. Estuarine Drift Sand The drift sand brought into the river mouth is related to the depth of the river. Following the discharge of water, deep erosion of the river bed leads to water logging and a rapid formation of sand bar/spit. These sand bars/spits take the shape of the front bay on both sides of the coast facing the sea, and drift sand is reduced. Depending on water discharge, the river mouth flow is reduced and drift sand collects. Figure 4.15.6 shows the return of the river mouth floor to its original state. 4. Conditions for Maintaining the River Mouth By comparing the strength of the flushing current and the drift in Sections 2 and 3, the conditions for maintaining the river mouth are obtained. In a river mouth, where closure occurs, as shown in the next section (4.15.3) the blockage can be prevented either by increasing the strength of the flushing current or reducing drift. However, as a rigorous estimate for the river mouth problem is difficult, measures should be taken gradually and normally. Construction

I cross section diagram

P

Fig. 4.15.5. Mechanism of scouring.

365

o &

i ■o i

(kg-m /day/m ) X 10~4 Fig. 4.15.6. Elements of the wave energy in the direction of the coast.

is carried out while observing the conditions. At a large river mouth which is affected by a tidal current the results obtained are shown in Fig. 4.15.7. Here, Q is the volume of the tidal prism and is shown by [(high tide; mean high tidal level-low tide; mean low tidal level) x (Area of the tidal spread at the mean tidal level)] and A represents the cross section area of the river mouth below the mean tidal level. The data for a stable cross section of the river mouth, considering both the drift sand movement caused by the tide and the strength of the flushing current of the river is exceedingly small. When the wave enters the shore at an angle, littoral drift occurs and because of this sand bars are formed at the river mouth. If the sand bar gradually increases naturally, the cross section of the flowing water will decrease. When the river current and the amount of littoral drift will be in a state of equilibrium, following which the development of the bar will stop. Figure 4.15.8 shows the cross section area A of the mouth after the development of a sand bar and the cross section A of water flow when there is no sand bar at the river mouth. The ratio A/Ai and the manner in which it changes depending on the nondimensional quantity Qx/ty for the coastal drift [3] are also shown in Fig. 4.15.8. The nondimensional ratio for the amount of coastal drift is given by

366

Fig. 4.15.7. Relationship between tidal prism and the area of cross section of river mouth.

Fig. 4.15.8. Relationship between quantum of littoral drift and mean maximum velocity of flushing current of the river and area of cross section of river mouth.

u*/ V{(a/p)-l}g propagation in the vicinity of fish bank (++), propagation away from fish bank (+), not connected with fish bank (-)

Swimming measured for 30 min to 1 hr

Maximum swimming speed

Hatchery

Distance moved is based on drift from landmark, biotelemetry

Distance covered

Water depth, water temperature, salinity, water quality, substrate are indicated under following heads: Standard propagation zone/limits of propagation zone

Egg diameter (longer axis)

Juvenile to preadult

From hatching to

Hatching (or incubation)

Standard distribution zone

Sexual generation, Preadult stage hatching, juvenile stage

Scientific name

Egg stage

Standard Japanese name

Animal

Stage of development

Name of species

Animal/plant

Proforma for animal species

1.3. Environmental Conditions for Propagation of Designated Species

Free moving/static spores, etc., period of development

Observations

Additional features

Enviromental conditions

Standard form

Male/female gametes

Mature gameto­ phyte

Standard distribution zone

Zygote of gametophore — premature

Premature stage

Period of reproduction Regional name in case of differences

Spores generated

Fully grown thallus

Representative nonedible living organisms which hinders development Form, shape or organ for adhesion

Nonedible living organisms

Organ for adhesion

Supplementary observations

Required degree of desiccation, endurance to drying

Endurance to waves, currents

Desiccation

Endurance

Water depth, water temperature, salinity, water quality, substrate, hydrography, intensity of illumination are shown in the manner given below: Standard propagation zone/limits of propagation zone

Male/female gamete producing stage

Reproduction

Stage of development

Standard size

Gametophyte

Standard Japanese name

Plant

Scientific name

Species

Flora and fauna

Proforma for plant species

383 Otaki’s Greenling Hexagrammos otakii Jordan Local name : Distribution : Period of reproduction :

Ainame Honshu-Hokkaido October to December

Parameter

Egg

Juvenile

Preadult

Adult

Standard size

1.8-2.2 mm

Total length: 7-70 mm

cf 12 cm Body length 10 cm 2 20 cm

Body length: 15-40 cm

Standard period

25 days (12°C)

Free swimming/ cfl year Juvenile: 60-80 2 2 years days

Egg character­ istics and food

Adherent, submerged

Plankton, benthic crustaceans

Shrimps, crabs, small fish

Shrimps, crabs, fish

Juvenile

Preadult

Adult

4 years

Conditions for propagation Parameter

Egg

Water depth, m

3-5/2-30

Water tempera­ ture, °C

12-15/10-25

Water quality

Highly trans­ parent/

Bottom matter

/Small stonesgravelly

Hydrography

Water zone of good tidal movement

/-150

/Gravelly

/Sandy mudgravelly

Preadult

Adult

Movement characteristics Parameter

Egg

Juvenile

Maximum free swimming speed

70 cm/sec

Hatchery

+++

Oxygen con­ sumption Obseivations

+++ 130 ml/kg h (22°C)

Seen in rainy places

384 Stone F lounder

Kareius bicoloratus Basilewsky Local name : Distribution : Period of reproduction :

Ishigare Honshu-Hokkaido coast December-January, Honshu

Development stages Parameter

Egg

Juvenile

Standard size

1.0-1.1 mm

Fingerling, total Total length: length: 3-11 mm; 7-20 cm Juveniles, total length: 1.2-6 cm

cf Body length: 20-30 cm 9 Body length: 30-50 cm

Standard period

6 days (10°C)

Fingerling: 50 days Juvenile: 3 months

2r-3 years

Egg characteristics and food

Free-floating, submerged

Copepods-larvae, Polychaetes, polychaetes mollusks

Shrimps, crabs, fish

Preadult

2 years

Adult

Conditions for propagation Parameter

Egg

Juvenile

Preadult

Adult

Water depth, m

30/10-16

20/10-30

5/1-20

20-40/5-70

Water tempera­ ture, °C

5-10/4-15.7

10-12/

Grain diameter, mm 0.125-0.5/ Mud-sand

Grain diameter, mm 0.125-0.5/ Mud-sand

Preadult

Adult

Salinity, %o

27-32.4/

Bottom matter

Movement characteristics Parameter

Egg

Juvenile

Oxygen con­ sumption Observations

26.0 ml/kg h (9.8°C) Weight of egg (ot) 22.5-24.3

In free floating period, aversion to light observed

385 M arbled Scorpionfish

Sebastiscus marmoratus (Cuvier and Valenciennes) Local name : Distribution : Period of reproduction :

Kasago Southern Hokkaido-Okinawa November-March

Development stages Parameter

Egg

Juvenile

Standard size

Fingerling: total length: 3.7-14 mm; Juvenile: total length: 1.5-2.0 mm

Standard period

Fingerling: 40 days

Egg char­ acteristics and food

Egg case

Preadult

Adult Total 16-20 cm

2 years Crustaceans

Fish, crustaceans

Preadult

Adult

Conditions for propagation Parameter

Egg

Juvenile

1-10

Water depth, m Water temperature, °C

Egg-laying 12-16/

15-21/

/-34

/30.7-35.0

Salinity %o

Stony-gravelly/

Bottom matter Movement characteristics Preadult

Adult

Hatchery

+++

+++

Oxygen consumption

55 ml/kg h (20°C)

Parameter

Egg

Juvenile

386 Schlegel’s Rockfish

Sebastes schlegeli Hilgendorf Local name : Distribution : Period o f reproduction :

Kurosoi Coastal zone of Japan April-June

Development stages Parameter

Egg

Juvenile

Standard size

Total length: 5-16 mm

Standard period

Fingerling: 25-30 days

Egg charac­ teristics and food

Egg case

Preadult

Adult Body length: 30-40 cm

Crustaceans, plankton

Fish, shrimps, crabs

Fish, shrimps, crabs

Juvenile

Preadult

Adult

40-60/

5-20/5-40

40-60/ 10-100

14-19/

8-12/

Condition for propagation Parameter

Egg

Water depth, m Water temperature, °C

14-17/

Salinity, %o

23.5-30.7/17.2-

Water quality

pH 8.1-8.4/

Bottom matter

Gravelly/

Gravelly/

Preadult

Adult

Movement characteristics Parameter

Egg

Juvenile

Sado Straits -* Tottori Coast

Distance covered ++

Hatchery Observations

Seen in seaweed

+++

Schlegel’s Porgy Accuithopagrus schlegeli (Bleeker) Local name Distribution : Period of reproduction :

Southern and Central Honshu May-August

Development stages Parameter

Egg

Juvenile

Preadult

Adult

Standard size

0.7-0.9 mm

Fingerling: total length: 2-10 mm; Juvenile: total length: 1-4 cm

Body length: 4-15 cm

C? Body length 17 40 cm ? Body / length 20

Standard period

40-45 h (20°C) Fingerling: 25 days, Juvenile: 3 months

2 years

3-4 years

Egg characteri­ stics and food

Free floating, submerged

Shrimps, crabs, Lam ell ibranches

Macrobenthons

Preadult

Adult

Crustaceans, plankton, Macrobenthons

Conditions for propagation Parameter

Egg

Water depth, m

Juvenile 2-5/

/-50 18-28/4-31

Water tempera­ ture, °C

14.5-22/1721

23-26/

Salinity, %o

31.3-33.4/

31-/

Water quality

SS, ppm /-100

Oxygen content, ml/1 /l-

Bottom matter

SS, ppm /-100

Sandy mud-fine sand/

Sandy mud-fine sand/

/Sandy mudgravelly

Juvenile

Preadult

Adult

Movement characteristics Parameter

Egg

140 cm/sec

Maximum free swimming speed ++

Hatchery Oxygen con­ sumption

518 ml/kg h (15-18°C)

Observations

Mainly at the bottom of seaweed areas

++ 169 ml/kg h (21.6°C)

Both male and female are similar up to 3-year-old fish.

388 Bluefin T una

Thunnus thynnus (Linn£) Local name Distribution : Period o f reproduction :

South sea-zone of Japan-Northeastern sea zone April-July

Development stages Parameter Egg

Juvenile

Preadult

Adult

Standard size

1.0-1.1 mm

Total length: 2.8-20 mm

Boby length: 3-150 cm

Body length: 160-250 cm

Standard period

About 24 h

1 month

1 month4 years

10-11 years

Egg char­ acteristics and food

Free floating, submerged

Copepods, juvenile fish

Fish, crustaceans, Fish, cephalopods cephalopods

Conditions for propagation Parameter

Egg

Juvenile

Preadult

Adult

Water depth, m

0-10/

0-10/ 0-50

20-50/ 0-50

20-50/ 0-20

Water tem­ perature, °C

22-27/ -28

24-28/ 22-

20-/ 14-28

15-20/ 5-30

Salinity, %o

32-35/ 30-

32-35/

28-35/

28-35/

Water quality

Oxygen content, ml/1 /3.7-6.8 pH/5.0-

Oxygen content, ml/1 4.0-6.0/ 1.0-

Oxygen content, ml/1 /4.0-6.0

Oxygen content, ml/1 /4.0-6.0

Juvenile

Preadult

Adult

Movement characteristics Parameter

Egg

4-5 km/day

Distance covered Hatchery

++ (-temporarily)

++ (-temporarily)

389 C hum Salm on

Oncorhynchus keta (Walbaum) Local name Distribution : Period of reproduction :

Chiba Prefecture, Honshu-North of Yamaguchi Prefecture September-January

Development stages Preadult

Adult

Parameter

Egg

Juvenile

Standard size

6.2-8.8 mm

Total length: 20-80 mm

Standard period

60 days (8°C)

Few days-2 months

C? 2-4 years 2 3-4 years

Egg characteris­ tics and food

Free floating, submerged

Zooplankton, insects

Zooplankton, juvenile squid

Macrozooplankton, pteropods, small fish

Juvenile

Preadult

Adult

Body length: 45-85 cm

Conditions for propagation Parameter

Egg

0-20/0-80

0-10/

Water depth, m Water tem­ perature, °C

5-8/4-12

4-10/-24

Water quality

Oxygen content, ml/1 -71 pH 6.1-6.5

Oxygen content, ml/1 -7/

Bottom matter

Grain diameter, mm 0.5-3.0/

Hydrography

Current speed, cm/sec 20-40/

-1 5 / -1.5-22.6

5-8/-1.5-20

Preadult

Adult

9-28 km/day

40 km/day

160-180 ml/kg h (10°C)

60.9-165.3 ml/kg h (9.0-15.3°C)

Movement characteristics Parameter

Egg

Juvenile

Distance covered Oxygen con­ sumption

9.5-25.7 ml/kg h (incubation, free floating)

Sea Bass Lateolabrax japonicus (Cuvier and Valenciennes) Local name : Distribution : Period o f reproduction :

Sukubi Coastal zone of Japan December-January

Development stages Parameter

Egg

Juvenile

Preadult

Standard size

1.2-1.4 mm

Fingerling: total length: 4.5-26 mm; Juvenile length: 2-4 cm

Body length: 5-20 cm

Standard period

108 h (15°C)

Egg char­ acteristics and food

Free floating, submerged

Adult c7*Body length 24.5 \ ? Body / length 34

1 year

1-7 years

Copepods

Mysids, shrimps, Crustaceans, plankton, mysids small fish

Conditions for propagation Parameter

Egg

Juvenile

Preadult

Adult

Water depth, m

0-5/

0-5/

5-58/

10-60/0-150

Water tem­ perature °C

15/ 12-20

15/15-20

15-20/ 15-24

10-28/ 5-30

Salinity, %o

/32.2-M.9

/5—35

/ l —35

Water quality

Oxygen content, ml/1 60-140/

Hydrography

Current velocity, cm/sec 65-75/

Movement characteristics Parameter

Egg

Juvenile

Preadult

Adult 65-75 cm/sec

Maximum free swimming speed Hatchery

++

Oxygen consumption

90-100 ml/kg h (12-25°C)

Observations

70 cm

Length under 5 Propagate in coastal sea-weed cm, upstream to freshwater zone areas

++ (winter period +++)

391 Brow n Puffer Fugu rubripes rubripes (Temminck and Schlegel) L ocal name Distribution : P eriod o f reproduction :

South and Central Hokkaido April-May

Development stages Parameter

Egg

Juvenile

Preadult

Adult

Standard size

1.2-1.4 mm

Total length: 2.6-45 mm

Total length: 4.5- ; Body length: 45 cm

Body length: 45-70 cm

Standard period

10 days (15-19°C)

60 days (fingerling: 30 days)

2 years

Egg char­ acteristics

Adherent, submerged

Crustacean, plankton

Shrimps, crabs, small fish

Shrimps, crabs, fish

Juvenile

Preadult

Adult

Conditions for propagation Parameter

Egg

Water depth, m

20/

Tidal zonebeach line/

Water tem­ perature, °C

15-19/

16-23/ 5-27

Salinity, %o

/Extensive salinity

Bottom matter

Grain diameter, mm 2-4/

Hydrography

Water zone of fast curmnt/

Observations

sandy mud/

Strong aversion to light

Distributed in steamy zones

16-23/5-27

392 B astard H alibut Paralichthys olivaceus (Temminck and Schlegel) L ocal name D istribution : P erio d o f reproduction :

Coastal zone of Japan March-May, Central Honshu

Development stages Parameter

Egg

Juvenile

Preadult

Standard size

0.8-1.0 mm

Fingerling: total length 2.2-13.5 mm; Juvenile: total length 1.4-5 cm

Total length: 5-30 cm

Standard period

65 h (15°C)

Fingerling: 40 days; Juvenile: 2 months

2 years

Egg char­ acteristics and food

Free floating, submerged

Fingerling: Mysids, shrimps, Fish, squids, Copepod larvae; small fish large crustaceans Juvenile: Mysids

Adult 4 _ /) + g, Here C