Coastal Engineering Coastal Engineering Processes, theory and design practice Dominic Reeve, Andrew Chadwick and Christopher Fleming First published 2004 by Spon Press 2 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN Simultaneously published in the USA and Canada by Spon Press 270 Madison Avenue, New York, NY 10016 Spon Press is an imprint of the Taylor & Francis Group This edition published in the Taylor & Francis e-Library, 2005. “To purchase your own copy of this or any of Taylor & Francis or Routledge’s collection of thousands of eBooks please go to www.eBookstore.tandf.co.uk.” ª 2004 Dominic Reeve, Andrew Chadwick and Christopher Fleming All rights reserved. No part of this book may be reprinted or reproduced or utilised in any form or by any electronic, mechanical, or other means, now known or hereafter invented, including photocopying and recording, or in any information storage or retrieval system, without permission in writing from the publishers. British Library Cataloguing in Publication Data A catalogue record for this book is available from the British Library Library of Congress Cataloging in Publication Data Reeve, Dominic. Coastal engineering : processes, theory and design practice / Dominic Reeve, Andrew Chadwick and Christopher Fleming. p. cm. Includes bibliographical references and index. ISBN 0–415–26840–0 (hb: alk. paper) — ISBN 0–415–26841–9 (pb: alk. paper) 1. Coastal engineering. I. Chadwick, Andrew, 1960– II. Fleming, Christopher. III. Title. TC205.R44 2004 6270.58—dc22 2004001082 ISBN 0-203-64735-1 Master e-book ISBN ISBN 0-203-67558-4 (Adobe eReader Format) ISBN 0–415–26840–0 (hbk) ISBN 0–415–26841–9 (pbk) Under heaven nothing is more soft And yielding than water. Yet for attacking the solid and the strong, Nothing is better; It has no equal. – Lao Tsu (6th Century B.C.) Contents List of tables xiii List of figures xiv List of symbols xxi Preface xxvii 1 Introduction 1 1.1 The historical context 1 1.2 The coastal environment 3 1.2.1 Context 3 1.2.2 Beach origins 3 1.2.3 Time and space scales 4 1.2.4 The action of waves on beaches 4 1.2.5 Coastal features 5 1.2.6 Natural bays and coastal cells 6 1.2.7 Coastal zone management principles 11 1.2.8 Coastal defence principles 12 1.3 Understanding coastal system behaviour 13 1.3.1 Introduction 13 1.3.2 Recognising shoreline types 14 1.3.3 Influences upon coastal behaviour 16 1.3.4 Generic questions 17 1.4 Scope 19 2 Wave theory 21 2.1 Introduction 21 2.2 Small-amplitude wave theory 24 2.2.1 Derivation of the Airy wave equations 24 2.2.2 Water particle velocities, accelerations and paths 26 2.2.3 Pressure variation induced by wave motion 27 2.2.4 The influence of water depth on wave characteristics 28 viii Contents 2.2.5 Group velocity and energy propagation 29 2.2.6 Radiation stress (momentum flux) theory 31 2.3 Wave transformation and attenuation processes 32 2.3.1 Refraction 32 2.3.2 Shoaling 34 2.3.3 Combined refraction and shoaling 36 2.3.4 Numerical solution of the wave dispersion equation 38 2.3.5 Seabed friction 39 2.3.6 Wave–current interaction 40 2.3.7 The generalised refraction equations for numerical solution techniques 42 2.3.8 The wave conservation equation in wave ray form 42 2.3.9 Wave conservation equation and wave energy conservation equation in Cartesian coordinates 45 2.3.10 Wave reflection 45 2.3.11 Wave diffraction 49 2.3.12 Combined refraction and diffraction 52 2.4 Finite amplitude waves 53 2.5 Wave forces 54 2.6 Surf zone processes 56 2.6.1 A general description of the surf zone 56 2.6.2 Wave breaking 58 2.6.3 Wave set-down and set-up 61 2.6.4 Radiation stress components for oblique waves 63 2.6.5 Longshore currents 63 2.6.6 Infragravity waves 66 Further reading 68 3 Design wave specification 69 3.1 Introduction 69 3.2 Short-term wave statistics 69 3.2.1 Time domain analysis 69 3.2.2 Frequency domain analysis 75 3.3 Directional wave spectra 78 3.4 Wave energy spectra, the JONSWAP spectrum 80 3.4.1 Bretschneider spectrum 82 3.4.2 Pierson–Moskowitz spectrum 83 3.4.3 JONSWAP spectrum 84 3.5 Swell waves 85 3.6 Prediction of deep-water waves 86 3.7 Prediction of nearshore waves 88 Contents ix 3.7.1 Point prediction of wind-generated waves 88 3.7.2 The SMB method 89 3.7.3 The JONSWAP method 90 3.7.4 Further modifications and automated methods 91 3.8 The TMA spectrum 93 3.9 Numerical transformation of deep-water wave spectra 95 3.9.1 Spectral ray models 96 3.9.2 Mild-slope equation 97 3.9.3 Non-linear models 99 3.10 Long-term wave climate changes 100 Further reading 101 4 Coastal water level variations 102 4.1 Introduction 102 4.2 Astronomical tide generation 103 4.2.1 Diurnal inequality 106 4.2.2 Tidal species 107 4.2.3 Spring-neap tidal variation 108 4.2.4 Tidal ratio 109 4.3 Tide data 111 4.4 Harmonic analysis 113 4.5 Numerical prediction of tides 115 4.6 Theory of long-period waves 115 4.7 Tidal flow modelling 120 4.8 Storm surge 130 4.8.1 Basic storm surge equations 130 4.8.2 Numerical forecasting of storm surge 131 4.8.3 Oscillations in simple basins 133 4.9 Tsunamis 135 4.10 Long-term water level changes 137 4.10.1 Climatic fluctuations 137 4.10.2 Eustatic component 138 4.10.3 Isostatic component 139 4.10.4 Global climate change 139 Further reading 141 5 Coastal transport processes 142 5.1 Characteristics of coastal sediments 142 5.2 Sediment transport 143 5.2.1 Modes of transport 143 5.2.2 Description of the threshold of movement 145 5.2.3 Bedforms 146 5.2.4 Estimation of bed shear stress 147 5.2.5 The entrainment function (Shields parameter) 151 5.2.6 Bedload transport equations 154 xContents 5.2.7 A general description of the mechanics of suspended sediment transport 156 5.2.8 Suspended sediment concentration under currents 160 5.2.9 Suspended sediment concentration under waves and waves with currents 165 5.2.10 Total load transport formulae 166 5.2.11 Cross-shore transport on beaches 171 5.2.12 Longshore transport (‘littoral drift’) 172 5.2.13 Concluding notes on sediment transport 179 Further reading 179 6 Coastal morphology: analysis, modelling and prediction 181 6.1 Introduction 181 6.1.1 Baseline review 182 6.2 Beach profiles 185 6.2.1 Analysis of beach profile measurements 185 6.2.2 The empirical orthogonal function technique 185 6.2.3 Other methods 189 6.2.4 Equilibrium profiles and the depth of closure 191 6.2.5 Numerical prediction of beach profile response 192 6.3 Beach plan shape 198 6.3.1 Plan shape measurements 198 6.3.2 Equilibrium forms 200 6.3.3 Beach plan shape evolution equation 201 6.3.4 Analytical solutions 203 6.3.5 Numerical solutions 207 6.4 Nearshore morphology 212 6.4.1 Introduction 212 6.4.2 EOF methods for beaches and the nearshore bathymetry 214 6.4.3 Combined wave, tide and sediment transport models 216 6.5 Long-term prediction 217 6.5.1 Limits on predictability 217 6.5.2 Probabilistic methods 223 6.5.3 Systems approach 227 7 Design, reliability and risk 229 7.1 Design conditions 229 7.1.1 Introduction 229 7.1.2 Extreme values and return period 229 7.1.3 Distribution of extreme values 235 7.1.4 Calculation of marginal extremes 240 7.1.5 Dependence and joint probability 244 Contents xi 7.2 Reliability and risk 249 7.2.1 Risk assessment 249 7.2.2 Structures, damage mechanisms and modes of failure 257 7.2.3 Assessing the reliability of structures 263 7.2.4 Level I methods 266 7.2.5 Level II methods 267 7.2.6 Level III methods 274 7.2.7 Accounting for dependence 277 7.2.8 Accounting for uncertainty 282 8 Field measurements and physical models 284 8.1 The need for field measurements and physical models 284 8.2 Field investigations 285 8.3 Theory of physical models 300 8.3.1 Generic model types 300 8.3.2 Similitude 300 8.4 Short-wave hydrodynamic models 303 8.5 Long-wave hydrodynamic models 305 8.6 Coastal sediment transport models 305 9 Conceptual and detailed design 312 9.1 The wider context of design 312 9.2 Coastal structures 318 9.2.1 Groynes 322 9.2.2 Shore-connected breakwaters 330 9.2.3 Detached breakwaters 337 9.2.4 Port and harbour breakwaters 342 9.2.5 Floating breakwaters 347 9.2.6 Sea walls 348 9.2.7 Sills 351 9.3 Natural coastal structures 353 9.3.1 Beach nourishment 354 9.3.2 Dune management 356 9.3.3 Tidal flats and marshes 359 9.4 Design guidance notes 360 9.4.1 Wave run-up 361 9.4.2 Wave overtopping and crest elevation 362 9.4.3 Armour slope stability 373 9.4.4 Crest and lee slope armour 389 9.4.5 Rock grading 390 9.4.6 Underlayers and internal stability 391 9.4.7 Crown walls 397 xii Contents 9.4.8 Scour and toe stability 398 9.4.9 Design of sea walls 406 9.4.10 Beach nourishment design 408 9.5 Design example 413 References 421 Appendix A Summary of statistical concepts and terminology 439 Appendix B Maximum likelihood estimation 445 Appendix C Harmonic analysis results 451 Index 453 Tables 2.1 Wave generation: to show group wave speed 31 2.2 Tabular Solution for breaking waves 38 3.1 Wave heights and periods 74 4.1 The main tidal harmonics 108 4.2 Harmonic analysis for the main tidal harmonics 115 4.3 Recommended rates of sea level rise for England 141 5.1 Numerical solution for suspended sediment transport 164 5.2 Annualised wave climate 178 5.3 Longshore transport results 178 7.1 Simple bounds for systems 249 7.2 Example of functional analysis for generic types of rock defence 253 7.3 Damage mechanisms for sea defences 258 7.4 Application of MVA 271 7.5 Application of Level III method 276 8.1 Similitude ratios for Froude similarity 303 8.2 Scaling laws for Kamphius’s bedload models 306 9.1 Significance of primary variables 315 9.2 The United Kingdom strategic framework 317 9.3