ENCYCLOPEDIA of HYDROLOGY

AND WATER RESOURCES

Kluwer Academic Encyclopedia of Earth Sciences Series

ENCYCLOPEDIA OF HYDROLOGY ANO WATER RESOURCES

Aim of the series

The Kluwer Academic Encyclopedia of Earth Sciences Series provides comprehensive and authoritative coverage of ali the main areas in the Earth Sciences. Each volume comprises a focused and carefuliy chosen coliection of contributions from leading names in the subject, with copious illustrations and detai1ed reference lists.

These books represent one of the world's 1eading reference resources for the Earth Sciences community. Previous volumes are being updated and new works published so that the volumes will continue to be essential reading for ali practising and research geologists, teachers and students.

Series Editor

Rhodes W. Fairbridge has helped edit 16 encyclopedias in the Kluwer Academic Encyclopedia of Earth Sciences Series (previously Chapman & Hali), as well as authoring over 300 other scientific publications. During his career he has worked as a petroleum geologist in the Middle East, been a W.W.II intelligence officer in the SW Pacific and led expeditions to the Sahara, Arctic Canada, Arctic Scandinavia, Brazii and New Guinea. He is now Emeritus Professor of Geology at Columbia University.

Volume Editor

Regina1d W. Herschy is the author of severa! other important hydrological works including Streamfiow Measurement, Chapman & Hali (second edition, 1995). He is Chairman of the International Standards Organisation's Subcommittee on Hydrometry, and is an Honorary Research Feliow at the University of Bristol's Department of Geography.

Previous volumes in the series

Schwartz: Encyclopedia of Beaches and Coasta! Environments, 1982 Finkl: Encyclopedia of Applied Geology, 1984 Oliver: Encyclopedia of Climatology, 1987 Finkl: Encyclopedia of Field and General Geology, 1988 Bowes: Encyclopedia of /gneous and Metamorphic Petrology, 1989 James: Encyclopedia of Solid Earth Geophysics, 1989

New and forthcoming volumes

Shirley: Encyclopedia of Planetary Sciences, 1997 Moores: Encyclopedia of European and Asian Regional Geology, 1997 Herschy: Encyclopedia of Hydrology and Water Resources, 1998 Alexander: Encyclopedia of Environmental Science Marshal: Encyclopedia of Geochemistry Gerrard: Encyclopedia of Geomorphology Finkl: Encyclopedia of Soi! Science and Technology 2ed

ENCYCLOPEDIA OF EARTH SCIENCES SERIES

ENCYCLOPEDIA of HYDROLOGY

AND WATER RESOURCES

edited by

REGINALD W. HERSCHY and RHODES W. FAIRBRIDGE

KLUWER ACADEMIC PUBLISHERS DORDRECHT/BOSTON/LONDON

Published by Kluwer Academic Publishers, P.O. Box 17, 3300 AA Dordrecht, The Netherlands

Sold and distributed in North, Central and South America by Kluwer Academic Publishhers, JOI Philip Drive, Norwell, MA 02061, U.S.A.

In ali other countries, sold and distributed by Kluwer Academic Publishers, P.O. Box 322, 3300 AH Dordrecht, The Netherlands.

First edition 1998 Reprinted with minor con·ections 1999

© 1998 Kluwer Academic Publishers

Typeset in 8/8Yzpt Times by Photoprint, Torquay, Devon

ISBN O 412 74060 5

Apart from any fair dealing for the purposes of research or private study, or criticism or review, as permitted under the UK Copyright Designs and Patents Act, 1988, this publication may not be reproduced, stored, or transmitted, in any form or by any means, without the prior permission in writing of the publishers, or in the case of reprographic reproduction only in accordance with the terms of the licences isued by the Copyright Licensing Agency in the UK, or in accordance with the terms of licences issued by the appropriate Reproduction Rights Organization outside the UK. Enquiries concerning reproduction outside the terms stated here should be sent to the publishers at the London address printed on this page.

The publisher makes no representation, express or implied, with regard to the accuracy of the information contained in this book and cannot accept any legal responsibility or liability for any errors or omissions that may be made.

A legal record for this book is available from the British Library

Library of Congress Catalog Card Number: 98-72142

8 Printed on permanent acid-free text paper, rnanufactured in accordance with ANSIINISO Z39.48-1992 and ANSIINISO Z39.48-1984 (Permanence of Paper)

"The man of science is of no country; ali mankind his countrymen"

James Smithson FRS (Founder of the Smithsonian Institution, 1846)

Contents

List of contributors xii Arai Sea 70 Foreword xvii R. W. Herschy

xviii Arid climates 70 Preface R. W. Durrenberger Acknowledgements xix Aridity indices 78 Selected international journals in hydrology and Stephen J. Stadler water resources XX Arid lands 83 Units, symbols and conversion factors xxii Peter G. Fookes Access to and accountability of water resources Arid zone hydrology 87 R. W. Herschy Denis A. Hughes Accuracy 3 Asia: climate 89 R. W. Herschy William A. Dando Accuracy of hydrodynamic approximations in hydrology: Atrnosphere 95 non-uniform, steady flow 11 C.G. Collier V.P. Singh and V. Aravamuthan Atmospheric processes associated with water in the atmosphere 96 Accuracy of hydrodynamic approximations in hydrology: C.G. Collier unsteady, uniform flow 26 Atrnospheric water vapor 98 V.P. Singh C.G. Collier Acidic deposition: acidification of surface waters 34 Australia: climate and water resources 98 M. Robbins Church Howard A. Bridgman Acid rain 36 Australian flood studies 109 John E. Oliver Elizabeth M. Shaw Activated sludge process: historical 38 Bernoulli energy equation 111 R. W. Herschy Philip G. Holland Activated sludge process 38 Biosphere 111 James R. Simpson Rhodes W. Fairbridge Africa: climate 43 Black Sea environment 111 John F. Griffiths R. W. Herschy Agroclimatology 50 Bottled water 112 Jen-Hu Chang R. W. Herschy Albedo and reflectivity 53 Caspian Sea 113 Samuel N. Goward R. W. Herschy Algal growth on lakes 56 Central America and West Indies: climate 113 R. W. Herschy George R. Rumney and John E. Oliver Alluvial valley engineering 56 Channelization and bank stabilization 117 Charles R. Kolb M.P. Mosley Amazon River 63 Chezy formula 121 Rhodes W. Fairbridge P.G. Holland Antarctic ozone hole 64 Chilgrove House well, UK 121 Jonathan Shanklin Terry J. Marsh Antecedent precipitation 69 Climate and climate change 122 Denis A. Hughes C.G. Collier Aquifer 69 Climate change and ancient civilization 130 Charlotte Schreiber Masatoshi M. Yoshino

viii CONTENTS

Climate change and the greenhouse effect 134 Drought management 214 R. W. Herschy Susan Walker

Climate data: sources 139 Droughts 215 Howard 1. Critchfield T.C. Sharma

Climate forecasting: monthly and seasonal 142 Echo sounding 222 Donald L. Gilman P.G. Holland

Clouds (cloud seeding) 143 El Nii'io 222 C.G. Collier William H. Quinn

Colebrook-White equation 144 Energy head 225 P.G. Holland P.G. Holland

Computer models 144 Entropy in environmental and water resources 225 Denis A. Hughes N.B. Harmancioglu and V.P. Singh

Conveyance 145 Environmental priorities for development: water 241 P.G. Holland R. W. Herschy

Correlation coefficient 145 Estuarine hydrology 244 A.H. Schumann R.E. Stevenson

Current metering 145 Europe, climate: a hydro1ogical perspective 248 P.G. Holland Keith R. Boucher

Cyanobacteria (b1ue-green algae) 147 Evaporation: measurement 264 Alan Howard W. C. Swinbank

Dams· 149 Evapotranspiration 266 Eric Best John E. Oliver

Dams: failure 153 Everglades, Florida, USA 271 R. W. Herschy Thomas D. Fontaine

Dams: world 155 Experimental basin 272 R. W. Herschy Mark Robinson

Danube River: hydrology and geography 159 Float 275 Petre Gâştescu P.G. Holland

panube River: development 161 Flood estimation: methods for developing countries 275 O. Starosolsdcy R. W. Herschy

Data processing in hydrology 162 Flood frequency analysis 279 Denis A. Hughes David Archer

De1taic plains 163 Flood hazard management 288 Charles R. Kolb Colin Green

Density for a minimum network of hydrological stations 172 Floods 293 World Meteorologica[ Organization Robert L. Wright

Desalination 174 Floods: largest in USA, China and the world 298 R. W. Herschy R. W. Herschy

Desert hydrology 176 Flood studies for the British Isles 300 Sharon E. Nicholson Elizabeth M. Shaw

Desertification 183 Flood studies worldwide 301 Sharon E. Nicholson Elizabeth M. Shaw

Deserts 186 F1oods: river and mu1ti-stage channe1s 302 Sharon E. Nicholson D.A. Ervine and A.B. MacLeod

Design ftood assessment 197 Floods: world's maximum observed 311 Elizabeth M. Shaw R. W. Herschy

Dew 197 Florida Bay: status and restoration 312 Rhodes W. Fairbridge and John E. Oliver David. T. Rudnick

Dewpoint 197 Flow measurement: new techno1ogy 313 Rhodes W. Fairbridge and John E. Oliver David W. Gibbard

Dew ponds 197 Flow through weirs, ftumes, orifices, sluices and pipes 319 R. W. Herschy R. W. Herschy

Drainage 202 Flume 330 Mark Robinson P.G. Holland

Drawdown, cone of depression 203 Fog and rnist 334 Charlotte Schreiber John A. Day

Drinking water and sanitation 204 Frequency analysis 335 R. W. Herschy World Meterological Organization

Drought 204 Frost 337 Donald Steila Benjamin Moulton

Drought in Western Europe, 1988-1992 211 Froude number 338 T.J. Marsh P.G. Holland

CONTENTS ix

Gauge (gage) 339 International rivers 432 P.G. Holland R.W Herschy

Gauging station 340 International standards in ftow measurement 440 P.G. Holland G.G. Robson

Ghyben-Herzberg theory 340 Irrigated land area: world 442 Ro ger J.M. De Wiest R.W Herschy

Global positioning system (GPS): overview 341 Irrigation and drainage 444 R.W Herschy World Meteorologica/ Organization

Global warming 342 Karst hydrology 447 R.W Herschy William Back

Greenhouse effect: general 342 Kissimmee River, Florida, USA 450 Zbigniew W Kundzewicz Louis A. Toth

Greenhouse effect 343 Lakes 451 A. lohn Arnfield Alee 1. Smith

Groundwater 345 L,ake Balaton, Hungary 454 Michael Price O. Starosolszky Groundwater: UK 348 Lake Chad 455 R.W Herschy J.H. Sircoulon Hydroclimatology 357 Lakes: effects on climate 455 Wayne M. Wendland Val L. Eichenlaub Hydrodynamics: porous media 360 Lakes, lake water 459 Adrian E. Scheidegger Petre Gâştescu Hydro-ecology: PHABSIM 361 Lakes: largest worldwide 461 R.W Herschy R.W Herschy Hydrogeology 363 Land-use change 466 F. C. Brassington A.H. Schumann Hydrogeology: history in USA 366 Limnology: definition 467 William Back Petre Gâştescu Hydrological cycle 367 Limnology 468 Robert M. Horden

Gerald A. Cale Hydrological mapping 371 Lough Neagh, UK 473 Gary D. Bishop and M. Robbins Church

P.G. Holland Hydrological services 374

Manning formula 475 World Meteorologica/ Organization P.G. Holland

Hydrological yearbooks 377 Maritime climate, oceanicity 475 T.J. Marsh Rhodes W Fairbridge and John E. Oliver

Hydrologists (600 sc-AD 1900) 378 Maritime zones 477 R.W Herschy Brian Goodall

Hydrology 400 Mathematical models 479 Ke ith Smith Zbigniew W Kundzewicz

Hydrology: coasta! terrain 404 Stuart A. Harris Maximum observed rainfalls 480

Hydrology: lakes and reservoirs 407 R.W Herschy

V.S. Vuglinsky Mean annual runoff: correlation with catchment characteristics 481

Hydrology: subsurface waters 407 R.W Herschy

Roger J.M. De Wiest Medicinal springs 481

Hydromechanics 410 Igho H. Kornblueh and Rhodes W Fairbridge

Michael E. McCormick Mediterranean climate 482

Hydrometeorology 411 Kamlesh P. Lulla

C.G. Collier Meteorology 483

Hydropower and energy-related projects 411 C.G. Collier

World Meteorologica/ Organization !y.Iixing 483

Hydrosphere 416 O. Starosolszky

Rhodes W Fairbridge Modeling of water resource systems 484

Infiltration: introduction 418 Susan Walker

A.H. Schumann Model predictions: uncertainty 486

Infi1tration 418 Keith Beven

J.R. Philip Models: distributed models of catchment hydrology 489

International databases 426 Keith Beven

World Meteorologica/ Organization Models: parameter estimation 492

International organizations involved with hydrology and Keith Beven

water resources 427 Monsoon climates 494 World Meteorologica/ Organization C.S. Ramage

X

Multi-parameter data loggers World Meteorologica/ Organization

Natura! disasters R.W Herschy

North America: climate George R. Rumney

Okeechobee Lake, Florida, USA: human impacts, research and lake restoration Nicholas G. Aumen and Karl E. Havens

Orographic precipitation James L. Guemsey

Paleohydrology Deborah Anthony and Ellen Wohl

Permafrost Troy 1. Pewe

Perrault, Pierre (1611-1680) J.H. Sircoulon

Popu1ation disp1acement due to dam construction R.W Herschy

Prandt1-von Karman equation P.G. Holland

Precipitation Louis ]. Battan

Precipitation distribution Orman E. Granger

Precipitation: source C.G. Collier

Probability of a hydrological event occurring in a given time interval World Meteorologica/ Organization

Qinghaihu Lake, China ling Yueling and Cui Dewei

Radar: precipitation-measuring (weather) radar in Europe R.W Herschy

Rain C.G. Collier

Raingauge Mark Robinson

Rain shadow: general A.H. Schumann

Rain shadow Sharon E. Nicholson

Razim-Sinoie 1ake complex, Romania Petre Gâştescu

Relative humidity Rhodes W Fairbridge

Remote sensing (1) Gareth Roberts

Remote sensing (2) Jean- Yves Scanvic and Philippe Dutartre

Remote sensing data: use in hydrological modeling Catherine Ottle

Reservoir capacity estimation World Meteorologica! Organization

Reynolds number P.G. Holland

River engineering G. Pender

Rivers R.W Herschy

River pollution prevention: historical R.W Herschy

Sahel region: climate and hydrology J.H. Sircoulon

CONTENTS

496

497

498

505

506

508

511

523

523

524

524

525

530

530

532

539

540

548

549

549

549

551

552

557

559

564

569

569

571

584

585

Saltwater wedge P.G. Holland

Sand dunes Sharon E. Nicholson

Sanitation and clean water R.W Herschy

Satellite hydrology: present trends and outstanding needs Eric C. Barrett

Savanna Sharon E. Nicholson

Sea level: mean Clifford Embleton

Seiche P.G. Holland

Semiarid regions David 1. Burdon

Sewage treatment: general introduction Diane Ireland

Sewage treatment processes R.W Herschy

Sink, sinkhole, swallow hole Rhodes W Fairbridge

Snow measurement David Archer

Snow C.G. Collier

Snowfall and snow cover: recent variations in northem high latitudes, present status of research and relevance to the climate change problem Pavel Ya. Groisman

Soi! and water management Robert L. Wright

South America Rhodes W. Fairbridge

Springs O.M. Hackett

Stage-discharge relation R.W Herschy

Storms: brief definitions R. W. Herschy

Streamftow measurement R.W Herschy

Surfacewater yield calculation Susan Walker

Suspended sediment monitoring: use of acoustic Doppler current profiler Giinther Reichel

Thames Barrier R.W Herschy

Thames, River T.J. Marsh

Thames W ater Ring Main R.W Herschy

Thiessen polygon A.H. Schumann

Trafalgar Square borehole, London, UK T.J. Marsh

Tree-rings in hydrological studies Thomas M. Yanosky and Malcolm K. Cleaveland

Tree-rings: Fortingall yew tree, UK R.W Herschy

United States Geo1ogical Survey: National Water-Use Information Program R.W Herschy

587

587

588

596

599

600

601

601

607

608

617

618

621

624

626

628

629

631

634

635

637

638

645

647

648

648

649

650

655

657

Unit hydrograph method in UK ftood studies Elizabeth M. Shaw Unsteady ftow model for computing streamftow United States Geological Survey

Urban hydrology Philip E. LaMoreaux and Lois D. George

Velocity-area method R.W Herschy W ater on Earth and other planets Rhodes W Fairbridge Water agencies: national and international Arthur J. Askew

WaterAid R.W Herschy W ater allocation and use R.W Herschy

Water availability and river water quality R.W Herschy W ater balan ce Robert M. Hordon Water budget analysis Robert A. Muller and John M. Grymes III W ater: categories Rhodes W Fairbridge Water charges (UK): abstractions and discharges R.W Herschy W ater di vining (1) F. C. Brassington

Water divining (2) R.W Herschy Waterfalls R.W Herschy

Water inventory V. Vuglinsky Water movement in unsaturated soils J.R. Philip

Water quality for drinking: WHO guidelines R.W Herschy

Water resources: introduction J.A. Cale

CONTENTS xi

659 Water resources: international 716 V.S. Vuglinsky

660 Water resources: dictionary of basic terms 717 P.G. Holland and R. W Herschy

666 Water resources: Europe 732

668 R.W Herschy

Water resources: integrated river basin management 748

671 David H. Newsome

Water resources: natural quality 749 673 R.W Herschy

Water resources: quality assessment 749 674 R.W Herschy

Water resources: surface and groundwater 757 676 R.W Herschy

Water: substance and solvent 762 677 Donald Langmuir and H.L. Bames

679 Water table 765 Michael Price

681 Water treatment: potable water 765 Peter Price

687 Water use 770 Philip Turton

688 Water use in the USA 775 R.W Herschy

689 Weathering 784

690 Rhodes W Fairbridge

W eber number 785 695 P.G. Holland

Weir: ftow measurement 785 698 P.G. Holland

World water balance 787 699 R.W Herschy

Y angtze Three Gorges Dam, China 791 706 R.W Herschy

712 Author index 793 Subject index 797

Contributors

Deborah Anthony College of Natural Resources Department of Earth Resources Colorado State University Fort Collins, CO 80523, USA

V. Aravamuthan Department of Civil Engineering Louisiana State University Baton Rouge, LA 70803-6405, USA

David Archer 2 Welburn Clase Ovingham, NE42 6BD, UK

A. John Arnfield Department of Geography, Ohio State University 103 Bricker Hall, 190 North Oval Mall Columbus, OH 43210-1361, USA

Arthur J. Askew World Meteorologica! Organization CH 1211, Geneva 2, Switzerland

Nicholas G. Aumen Okeechobee Systems Research Division South Florida Water Management District PO Box 24680 West Palm Beach, FL, 33416-4680, USA

William Back United States Geological Survey Reston, V A 22092, USA

Hubert L. Bames Earth and Mineral Sciences Pennsylvania State University, 235B Deike Building University Park, PA 16802, USA

Eric C. Barrett Remote Sensing Centre, Department of Geography University of Bristol Bristol BS8 1SS, UK

Louis J. Battan ( deceased)

Eric J. Best Canberra College of Advanced Education, PO Box 1, Belconnen ACT 2616, Australia

Keith Beven Institute of Environmental and Biologica! Sciences Lancaster University Lancaster LAI 4YQ, UK

Gary D. Bishop US Environmental Protection Agency 200 SW 35th Street Corvellis, OR, USA

Keith R. Boucher Department of Geography Loughborough University of Technology Loughborough LEII 3TU, UK

F.C. Brassington 12 Culcheth Hall Drive, Culcheth Warrington WA3 4PS, UK

Howard A. Bridgman Department of Geography University of Newcastle Newcastle, NSW 2308, Australia

David J. Burdon Food and Agricultura! Organization of the United

Nations via DelleTerme di Caracella Rome, Italy

M. Robbins Church US Environmental Protection Agency 200 SW 35th Street Corvellis, OR, USA

Jen-Hu Chang Department of Geography University of Hawaii, Porteus Hali 445, 2424 Maile Way Honolulu, Hawaii 96822, USA

Malcolm K. Cleaveland Department of Geography University of Arkansas Fayetteville, AR 72701, USA

Gerald A. Cole Department of Zoology Arizona State University Tem pe, AZ 85281, USA

J.A. Cole 3 Grangefield W ay, Aldwick Bognor Regis, P021 4EG, UK

C.G. Collier Department of Civil Engineering Telford Research Institute Salford University Salford, M5 4WT, UK

Howard J. Critchfield Office of the State Climatologist Western Washington University Bellingham, W A 98225, USA

Cui Dewei Hydrological Service of Qinghai Province 82, Kunlun Road, Xining People' s Republic of China

William A Dando Department of Geography University of North Dakota Grand Forks, ND 58201, USA

John A. Day 609 North Cowls McMinnville, OR 97128, USA

R.W. Durrenberger 6233 East Catalina Drive Scottsdale, AZ 85251, USA

Philippe Dutartre BRGM, BP 6009 45060 Orleans, Cedex 2, France

CONTRIBUTORS

Val L. Eichenlaub Department of Geography Western Michigan University Kalamazoo, MI 49008, USA

Clifford Embleton (deceased)

D.A. Ervine Department of Civil Engineering University of Glasgow, Oakfield Avenue Glasgow, Gl2 8LT, UK

Rhodes W. Fairbridge 420 Riverside Drive, Apt 2-B New York, NY 10025, USA

Thomas D. Fontaine Department of Research South Flori da W ater Management District West Palm Beach, FL 33416--4680, USA

Peter G. Fookes Winters Wood, 47 Crescent Road Caterham, CR3 6LH, UK

Petre Gâştescu Institute of Geography, Romanian Academy Dimitrie Racovita, 12 Bucharest 70307, Romania

Lois D. George Alabama Geological Survey, PO Drawer O University, AL 35486, USA

David W. Gibbard Kingsworthy, Winchester S023 7QA, UK

Donald L. Gilman W /NMC51, National Oceanic and Atmospheric

Administration National Weather Service Washington, DC, USA

Brian Goodall Department of Geography University of Reading, Whiteknights Reading, RG6 2AB, UK

Samuel N. Goward Department of Geography, Social Sciences Building University of Maryland College Park, MD 20742, USA

Orman E. Granger Department of Geography University of California Berkeley, CA 94720, USA

xiii

xiv CONTRIBUTORS

Colin Green Flood Hazard Research Centre Middlesex University, Queensway Enfield, EN3 4SF, UK

John F. Griffiths Texas A and M University College of Geosciences College Station, TX 77843, USA

Pavel Y a. Groisman Department of Geology and Geography University of Massachusetts at Amherst Amherst, MA 01003-0026, USA

John M. Grymes III Southem Regional Climate Center Department of Geography and Anthropology Louisiana State University Baton Rouge, LA 70803-4105, USA

Jarnes L. Guemsey Department of Geography and Geology Indiania State University Terre Haute, IN 47809, USA

O.M. Hackett US Geological Survey Washington, DC 20242, USA

N.B. Harmancioglu Department of Civil Engineering Louisiana State University Baton Rouge, LA 70803-6405, USA

Stuart A. Harris Department of Geography University of Calgary, Canada

Karl E. Havens Okeechobee Systems Research Division South Florida Water Management District PO Box 24680 West Palm Beach, FL 33416-4680, USA

R.W. Herschy 2, Queensborough Drive Reading, RG4 7JA, UK

P.G. Holland 21, Glencregagh Road Belfast, BT8 4FZ, UK

Robert M. Hordon Department of Geography Rutgers University New Brunswick, NJ 08903, USA

Alan Howard Department of Geography University of Reading, Whiteknights Reading, RG6 2AB, UK

Denis A. Hughes Institute for Water Research Rhodes University Grahamstown, PO Box 94, South Africa

Diane Ireland 14, Southlands, Kirkharn Preston PR4 2TR, UK

Jing Yueling Hydrological Service of Qinghai Province 82 Kunlun Road, Xining People's Republic of China

Charles R. Kolb (deceased)

Igho H. Komblueh Department of Physical Medicine University of Pennsylvania Philadelphia, PA 19146, USA

Zbigniew W. Kundzewicz World Meteorologica} Organization CH 1211, Geneva 2, Switzerland

Philip E. LaMoreaux Philip E. LaMoreaux and Associates Inc. PO Box 2310 Tuscaloosa, AL 35403, USA

Donald Langmuir Colorado School of Mines 129 S. Eldridge Way, Golden Colorado 80401, USA

Kamlesh P. Lulla Department of Geography and Geology Indiana State University Terre Haute, IN 47809, USA

A.B. MacLeod Department of Civil Engineering University of Glasgow, Oakfield Avenue Glasgow, 012 8LT, UK

T.J. Marsh Institute of Hydrology Wallingford, OX10 8BB, UK

Michael E. McCormick Department of Ocean Engineering US Naval Academy Annapolis, MD 21402, USA

CONTRIBUTORS

M.P. Mosley W ater and Soil Science Centre Ministry of W orks and Development PO Box 1479 Christchurch, New Zealand

Benjamin Moulton Department of Geography and Geology Indiana State University Terre Haute, IN 47809, USA

Robert A. Muller Southern Region Climate Center Department of Geography and Anthropology Louisiana State University Baton Rouge, LA 70803, USA

David H. Newsome CNS Scientific & Engineering Services 5 Alderney Court, Montagu Street Reading, RG1 4JN, UK

Sharon E. Nicholson Department of Meteorology Florida State University 404 Love Building 3034 Tallahasse, FL 32306, USA

John E. Oliver Department of Geography, Geology and Anthropology Indiana State University Terre Haute, IN 47809, USA

Catherine Ottle CRPE, Centre Universitaire 10/12 Avenue de l'Europe Velizy, 78140, France

G. Pender Department of Civil Engineering University of Glasgow, Oakfield Avenue Glasgow, G12 8LT, UK

Troy L. Pewe 538 East Fairmont Drive Tempe, AZ 85282, USA

J.R. Philip Centre for Environmental Mechanics CSIRO, GPO Box 821 Canberra, ACT 2601, Australia

Michael Price PRIS, University of Reading PO Box 227, Reading, RG6 2AB, UK

Peter Price 6 Aldford Close, Bromborough Wirral, L63 OPT, UK

William H. Quinn School of Oceanography Oregon State University Corvallis, OR 97331, USA

C.S. Ramage Department of Meteorology University of Hawaii 2525 Correa Road Honolulu, HI 96822, USA

Giinther Reichel Gumpendorferstrasse 72/7 1060 Vienna, Austria

Gareth Roberts Institute of Hydrology Wallingford, OX10 8BB, UK

Mark Robinson Institute of Hydrology Wallingford, OXlO 8BB, UK

G.G. Robson British Standards Institution 389 Chiswick High Road London, W4 4AL, UK

David T. Rudnick Everglades Systems Research Division South Flori da W ater Management District PO Box 24680 West Palm Beach, FL 33416-4680, USA

George R. Rumney 3, Ridge Road Groton Long Point, CT 06340, USA

Jean-Yves Scanvic BRGM, PO Box 6009 A venue de Concyr, Orleans Cedex 2, 45060, France

Adrian E. Scheidegger Institut fiir Geophysik Technische Universităt Wien Gusshausstrasse 27-29 Vienna, A 1040, Austria

Charlotte Schreiber Department of Earth Science Queens College Flushing, NY 11367, USA

A.H. Schumann Institute of Hydrology Ruhr University Bochum Universităt Str. 150 44801 Bochum, Germany

XV

xvi

J onathan Shanklin British Antartic Survey Cambridge, CB3 OET, UK

T.C. Sharma School of Environmental Studies PO Box 3900, Moi University Eldoret, Kenya

Elizabeth M. Shaw The Meadows, Castle Park, Hornby Lancaster, LA2 8SB, UK

James R. Simpson Westbank, New Ridley, Stocksfield Northumberland, NE43 7RQ, UK

V.P. Singh Department of Civil Engineering Louisiana State University Baton Rouge, LA 70803-6405, USA

J.H. Sircoulon French National Committee (IAHS) Orstom, 213 Rue Lafayette, Paris, Cedex 75480, France

Alee J. Smith Department of Geology University College London, UK

Keith Smith School of Natural Sciences University of Stirling Stirling, FK9 4LA, UK

Stephen J. Stadler Department of Geography Oklahoma State University Stillwater, OK 74078, USA

b. Starosolszky VITUKI, Water Resources Research Centre PLC 1095 Budapest IX Kvassay Jenă UT, Hungary

Donald Steila Department of Geography and Earth Sciences University of North Carolina Unce Station Charlotte, NC 28223, USA

R.E. Stevenson Scripps Institute of Oceanography La Jolla, CA 92037, USA

W.C. Swinbank (deceased)

CONTRIBUTORS

Louis A. Toth Department of Research South Florida Water Management District West Palm Beach, FL 3341~680, USA

Philip Turton 16, Matlock Road Reading, RG4 7BS, UK

United States Geological Survey National Center, Mail Stop 415 Reston, V A 22092, USA

V.S. Vuglinsky State Hydrological Institute 23 Second Line 19905 St Petersburg, Russia

Susan Walker The Environment Agency PO Box 12, Richard Fairclough House Knutsford Road Warrington, WA4 lHG, UK

Wayne M. Wendland Climatology Section Illinois State Water Survey Champaign, IL, USA

Roger J.M. De Wiest Departrnent of Geological Engineering Princeton University Princeton, NJ 08540, USA

Ellen Wohl College of Natural Resources Department of Earth Resources Colorado State University Fort Collins, CO 80523, USA

World Meteorologica! Organization CH 1211, Geneva 2, Switzerland

Robert L. Wright Department of Geography University of Sheffield Sheffield, SlO 2TN, UK

Thomas M. Yanosky United States Geological Survey National Center, Mailstop 415 Reston, V A 22092, USA

Masatoshi M. Y oshino Institute of Geoscience University of Tsukuba Ibaraki, 305, Japan

Foreword

In my pos1t10n over the last few years as Chief Hydrologist of the US Geological Survey, I have seen the increasing scarcity of the available water resources of the United States and those of the world. Users compete for a renewable resource that is becoming stressed in many locations. These stresses include demands for water for agricultura}, industrial and domestic uses as well as demands for water in streams for purposes of preserving or enhancing habitat and water quality. Information is needed by those engineers and hydrologists and by informed lay persons in order better to utlilize and allocate water.

In the Encyclopedia of Hydrology and Water Re­sources, the editors have assembled the combined efforts of both practitioners and academics, who as world experts have provided some of the latest information in their fields. These diverse sources of knowledge have resulted in a reference work that should prove to be most useful as we move into the twenty-first century.

Of particular utility is the inclusion of water resources as well as the more traditional science of hydrology.

This encyclopedia covers many aspects of hydrology and water resources, including water pollution.

It is difficult for members of a busy general audience to quickly tind up-to-date, summarized information on hydrology and water resources. Planners, policy makers, regulators and decision makers are the primary audience for this source of information.

In many parts of the world people face conflict and difficult choices as they consider how to manage their water resources. Many of these problem areas are given excellent coverage in the encyclopedia, which describes the situations in terms of water resources availability, water quality and management options.

With pleasure I recommend the Encyclopedia of Hydrology and Water Resources to those that need quick, authoritative information in these fields. This reference should prove particularly useful to the applied hydrolo­gist and to those in academia.

Robert M. Hirsch Chief Hydrologist, United States Geological Survey

Preface

The hydrological cycle is the source and substance of life on Earth. It took a thousand years to explain its concept and yet we still do not fully understand it. However we have come a long way from the concept of the early philosophers that the formation of rivers was due to sea water being forced · somehow into huge cavems in the mountains.

In the world today, millions of people die each year because of poor water management and over 25 coun­tries are still classified as water-scarce countries affect­ing human activity, health and growth. This encyclo­pedia does not pretend to embrace all aspects of the subject of hydrology and water resources; to do so would require severa! volumes. However, it contains an eclectic selection of numerous topics linked by the common thread of hydrology and water resources in the service of humanity. This volume is essentially a potpourri of miscellany that follow an applied theme where each topic may be considered an apophereta, something to be savored for the information it contains. Because it is not possible to consider every aspect of the subject in a reference work of this level and with a mandate so broad, the encyclopedia represents an attempt to provide an overview of diverse topics through a sample of a wide range of interrelated topics.

All entries are in alphabetical order with the length largely related to the importance of the topic. The reader may tind that the same topic may be dealt with from various viewpoints in a number of different entries.

To tind a particular topic, it is best to look first for that subject in its alphabetical context. Beyond that, the index and cross references will provide further guidance to the subject in question. The comprehensive index at

the back of the volume will list, for a given term or name, every page in the book where that item appears. This is a fine way to tind a subject presented in many different contexts. On the other hand, the cross refer­ences at the end of each entry act as a guide to other related entries. Wherever possible, extensive lists of references are appended to each entry. The opportunity was taken of examining previous encyclopedias in the series for suitable entries on hydrology and water resources and a selection of these was considered and updated where necessary. Due acknowledgement is therefore made to the authors and publishers for permis­sion to publish these contributions in this volume. The encyclopedias utilized were:

Geomorphology, 1968. Reinhold Book Corporation, New York.

Geochemistry and Environmental Sciences, 1972. Dowden Hutchinson & Ross Inc, Stroudsburg, PA.

Applied Geology, 1984. Van Nostrand Reinhold Company, New York.

Climatology, 1987. Van Nostrand Reinhold Company, New York.

The creation of this encyclopedia, like others in the series, would not have been possible without the wholehearted cooperation of our contributors; there are over 114 of them in this volume and 17 different countries are represented.

Rhodes W. Fairbridge, Series Editor Reginald W. Herschy, Volume Editor

Acknowledgements

The editors are deeply grateful to the following authors, publishers and organizations for granting permission to quote from books and papers published by them.

• Ashtec Europe Ltd, UK • A.A. Balkema, Rotterdam • C.V. Beadon, UK • Asit K. Biswas, UK • British Society of Dowsers, UK • British Standards Institution, London • Chapman & Hali, London • Chartered Institution of Water and Environmental

Management, London • CRC Press Inc./Lewis Publishers, USA • Department of the Environment, Water Directorate,

UK • J.C.I. Dooge, Ireland • EARSeL, Paris • Elsevier Science Ltd, Oxford, UK • Environment Agency, UK • The European Environment Agency; The Dobris

Assessment, Copenhagen

• Sir Hugh Fish, UK • Foundation for Water Research, UK • Geological Society of America, Boulder, USA • Institute of Hydrology/ODA, UK • Institution of Civil Engineers, London • International Association of Hydrological Sciences • International Bottled Water Association, USA • International Commission on Large Dams, Paris • International Desalination Association, USA • International Standards Organization, Geneva • International Water Supply Association, London • Smithsonian Institution, Washington, DC • Sterling Publications, London • UK Groundwater Forum, W allingford, UK • United Nations, New York • United States Geological Survey, Reston, USA • WaterAid, London • John Wiley and Sons, New York • World Bank, Washington, DC • World Health Organization, Geneva • World Meteorologica! Organization, Geneva

Selected international journals in hydrology and water resources

Advances in Water Resources Elsevier Science, Oxford, UK Advances in Water Science PRC, Beijing Agriculture and Forest Meteorology Elsevier Science, Amsterdam Agricultura/ Water Management Elsevier Science, Amsterdam Applied Hydrogeology (/AH) Verlag Heinz Hesse, Hanover,

Germany Aqua Blackwell, Oxford Aqua Fennica Aqua Fennica, Finland Aquatic Conservation John Wiley, Chichester, UK Bulgarian Journal of Meteorology and Hydrology Bulgarian

Academy of Science, Sofia, Bulgaria Bulletin of The American Meteorologica/ Society AMS Boston,

USA Bulletin de Liaison du Comite Interafricain d'Etudes Hydrauliques

Orston, Paris Ceres (FAO) FAO, Rome Climate Monitor University of East Anglia, UK Climate Change Kluwer, Dordrecht, Netherlands Dams and Reservoirs British Dam Society of ICE, London Danish Hydraulics DHI, Horsholm, Denmark Deutsche Gewasser Kundliche Mitteilungen Schriftleitung, Koblenz Earth Surface Processes and Landforms John Wiley, Chichester,

UK Ecologica/ Monitoring Elsevier, Amsterdam Environmental Science and Technology American Chemical Society,

Ohio, USA Environmetrics John Wiley, Chichester, UK Geographical Journal Royal Geographical Society, London Global Planetary Change Elsevier Science, Amsterdam Groundwater Groundwater Pub. Co., Westerville, Ohio Groundwater Monitoring & Remediation Groundwater Pub. Co.,

Westerville, Ohio Houille Blanche Soc. Hydrotechnique de France, Paris Hydrogeologie BRGM, Orleans, France Hydrogeology Journal Verlag Heinz Heise, Hanover, Germany Hydrological Processes John Wiley, Chichester, UK Hydrological Sciences Journal IAHS, Wallingford, UK Hydrology and Earth System Sciences EGS, Katlenburg-Lindau

Germany Hydroplus Levallois Penet, France Hydrotitles Geosystems, Oxford, UK ICID Journal ICID, New Delhi, India International Journal of Climatology John Wiley, Chichester, UK International Journal of Geographical lnformation Systems Taylor

and Francis, London International Journal an Hydropower and Dams Aqua-Media

International, UK

International Journal of Remote Sensing Taylor and Francis, London

International Joumal of Water Resources Development Carfax, Oxford, UK

International Water Power and Dam Construction: Wilmington Business Pub., UK

lrrigation Science Springer-Verlag, Heidelberg, Germany Journal of American Water Resources Association A WRA, Hendon,

VA, USA Journal of Applied Ecology Blackwell Science, Oxford Journal of Applied Hydrology (India) Association of Hydrology,

Visakhapatnam, India Journal of Applied Meteorology American Meteorologica! Society,

Boston, MA, USA Journal of Atmospheric Sciences American Meteorologica! Society,

Boston, MA, USA Journal of Climate American Meteorologica! Society, Boston, MA,

USA Journal of Contaminant Hydrology Elsevier Science, Amsterdam Journal of Environmental Engineering (ASCE) American Society of

Civil Engineers, New York Journal of Hydraulic Research IAHR, Delft, Netherlands Journal of Hydrology Elsevier Science, Amsterdam Joumal of Hydrology (New Zealand) New Zealand Hydrological

Society, W ellington Joumal of Hydroscience and Hydraulic Engineering (Japan)

Japanese Society of Civil Engineers, Tokyo Joumal of the Chartered Institution of Water and Environmental

Management CIWEM, London Journal of Irrigation and Drainage Engineering (ASCE) American

Society of Civil Engineers, New York Journal of Meteorology Artetech Pub. Co., UK Joumal of Water Resources Planning and Management (ASCE)

Americas Society of Civil Engineers, New York Land and Water International (Netherlands) NEDECO, The Hague Monthly Weather Review American Meteorologica! Society, Boston,

MA, USA New Civil Engineer Thomas Telford (ICE), London Nordic Hydrology Nordic Association for Hydrology, Lyngby Proceedings of the Institution of Civil Engineers ICE, London Rivers SEL and Associates, Colorado, USA Russian Meteorology and Hydrology Allerton Press, New York Soil Science Williams and Wilkins, Baltimore, USA Soil Science Society of America Joumal SSSA, Madison, WI, USA Stochastic Hydrology and Hydraulics Springer International,

Heidelberg, Germany Transactions American Geophysical Union - EOS American

Geophysical Union, Washington, DC

INTERNATIONAL )OURNALS IN HYDROLOGY AND WATER RESOURCES xxi

Transactions of the lnstitution of Engines of Australia, Civil Engineering Institution of Engineers of Australia, Barton

Water Air and Soi/ Pollution Kluwer, Netherlands Water and Atmosphere NIW A, New Zealand Water and Environment International Argus Business Media UK Water International IA WQ, IL, USA Water Quality International IA WQ, London Water Research Pergamon Press Water Resources Bulletin American Water Resources Association,

VA, USA Water Resources Joumal (UNESCAP) United Nations, Bangkok Water Resources Management Kluwer, Netherlands Water Resources Research Amer. Geophysical Union, Washington,

DC Water SA South African Water Research Committee, Pretoria

Water Science and Technology (IA WQ) Elsevier Science, Oxford Waterlines Intermediate Technology Pub, London Waterwav (UNESCO IHP) UNESCO, Paris Weather.Royal Meteorologica!, Society, UK WMO Bulletin WMO, Geneva World Climate News WMO, Geneva World Water and Environmental Engineering Faversham House

Group, UK

R.W. Herschy

Source

The Institute of Hydrology (UK) Library.

Units, symbols and conversion factors

Standard units are used for the measurement of length, area, volume, velocity, discharge, density, mass, pressure, gravitational acceleration and temperature. The Systeme International d'Unites (SI), as estab­lished by the International Organization for Standardization in 1960, is generally used throughout this volume, but the English system ( customary units) is used where appropriate.

SI units

Historical note

The idea of decima! units of measurement was conceived by Simon Stevin (1548-1620), who also developed the even more important concept of decima! fractions. Decima! units were also considered in the early days of the French Academie des Sciences founded in 1666, but the adoption of decima! weights and measures was part of the general increase in administrative activity in Europe which followed the French Revolution. The statesman Talleyrand aimed at the establishment of a system of international decima! units of weights and measures 'a tous les temps, a tous les peuples'. On the advice of the scientists of his day, these were based on the meter as the unit of length and the gram as the unit of mass. The meter was intended to be one ten-millionth part of the distance from the North Pole to the equator at sea level, and passing through Paiis; the gram was to be the mass of 1 cubic centimeter of water at its maximum density, at a temperature of approximately 4°C. A system of prefixes was developed to indicate powers of ten of the units, thus providing a flexible and convenient means of expression for a wide range of magnitudes and avoiding the need to use very large or very small numerica! values. The prefixes also enabled the units of different sizes to be memorized with ease.

Although the decima! units were primaiily devised as a benefit to industry and commerce, scientists soon realized their advantage and they were adopted in scientific and technical circles in continental Europe and in the UK. In 1832 Gauss arbitrarily chose length, mass and time as three 'fundamental' or base quantities and showed that magnetic flux could be calculated in terms of these; in 1851 Weber extended the theory to include ali electrica! quantities. Duiing the period 1861-1867 the British Association Committee on Standards of Electrica! Resistance adopted the electromagnetic units as outlined by Weber and !ater also adopted a system of 'practica!' units (the ohm, am pere and joule ), each of which was related by some power of ten to the corresponding unit of the fundamental system. In 1873 a further BA Committee recommended the general adoption by ali scientists of the centimeter, the gram and the second as the units of measurement for the three 'fundamental' quantities, thus establishing the CGS system of units. In 1901 Professor Giorgi proposed that the base units be changed to the meter, the kilogram and the second (the MKS

system) and to these he added an electrica! base unit. The Inter­national Electrotechnical Commission adopted MKS in 1935 but the choice of the ampere as the electiical base unit was not made until 1950, giving the MKSA (or Giorgi) system covering both mechanics and electromagnetism.

Following the signing of the Metre Convention in Paris in 1875, the Conference Generale des Poids et Mesures (CGPM) has been responsible for ali international matters concerning the meter and the kilogram and with metrological studies in relation to these quantities; this responsibility was widened in 1921 to cover ali units of measure­ment. The CGPM meets in Paris and under its authority to deal with scientific aspects of its work are the Comite International des Poids et Mesures (CIPM) assisted by various Consultative Committees, and the Bureau International des Poids et Mesures (BIPM). The labor­atories of BIPM at Sevres are the repository of the prototype kilogram and the former prototype meter. The kilogram is still defined in terms of the international prototype at Sevres but the meter is now defined in terms of a specified number of wavelengths of a particular radiation of light.

At its tenth meeting, in 1954, the CGPM adopted a coherent system of units based on the four MKSA units together with the kelvin as the unit of tempera ture and the candela as the unit of luminous intensity. The eleventh CGPM in 1960 formally gave it the full title 'Systeme International d'Unites' for which the abbreviation is 'SI' in ali languages. At the fourteenth CGPM, in 1971, the mole (symbol moi) was adopted as the unit for amount of substance and as the seventh base unit. Two additional special names (and symbols) were also adopted as foliows: pascal (Pa) for newton per square meter and siemens (S) for reciproca! ohm. At the fifteenth CGPM, in 1975, two further special names (and symbols) were adopted: becquerel (Bq) for reciproca! second and gray ( Gy) for joule per kilogram, as well as the additional prefixes peta (P) for 1015 and exa (E) for 1018•

The International System of Units (SI)

This system includes three classes of units:

• base units; • supplementary units; • derived units.

Together these fmm the coherent system of SI units.

Base units

The SI is founded on the seven base units listed in Table 1.

Supplementary units The CGPM has not yet classified certain units of the SI as either base units or derived units.

UNJTS, SYMBOLS ANO CONVERSJON FACTORS

Table 1 Ba se un its

Quantity

Length Mass Time Electric current Thermodynamic temperature Amount of substance Luminous intensity

Table 2 Supplementary units

Name of base SI unit

meter kilogram second am pere kelvin mole candela

Quantity Name of supplementary SI unit

Plane angle Solid angle

radian steradian

Symbol

m kg

A K moi cd

Symbol

rad sr

These units, listed in Table 2, are called 'supplementary units' and may be regarded either as base units or as derived units.

Table 4 Prefixes

Factor by which the unit is multiplied

1018 1015 1012 109

106

103 IO' JOI w-1 w-2 w-J w-6 w-9 10-12 10-1s w-~~

xxiii

Prefix

Name Symbol

exa E pe ta p tera T giga G mega M kilo k hecto h deca da deci d centi c milli m micro IL nano n pica o femto f atto a

Derived units Derived units are expressed in terms of base units and/or supple­mentary units by multiplication and division; for example, the SI unit for velocity is meter per second (m s-1) and the SI unit for angular velocity is radian per second (rad s- 1).

multiples and submultiples are formed by adding prefix symbols to the symbol g.

Examples of multiples of SI units include:

lcm3 =(I0-2 m)3 =10-6 m3

For some of the derived SI units, special narnes and symbols exist; those approved by the CGPM are listed in Table 3.

j J.LS-1 = (10-6s)-1 = 106s-1 1 mm2 s- 1 = oo-3 m)2 s- 1 = w-6 m2 s-1

Compound prefixes should not be used; for example, use nm (nanometer) and not 'mJ.Lm'.

It may sometimes be advantageous to express derived units in terms of other derived units having special names; for example, the SI unit for electric dipole moment is usually expressed as C m, but can be expressed as A s m. Use of SI units and their multiples

Multiples of SI units The prefixes given in Table 4 (SI prefixes) are used to form names and symbols of multiples (decima! multiples and submultiples) of the SI units.

The choice of the appropriate multiple (decima! multiple or sub­multiple) of an SI unit is governed by convenience, the multiple chosen for a particular application being the one which will lead to numerica! values within a practica! range.

The symbol of a prefix is considered to be combined with the unit symbol to which it is directly attached, forming with it a symbol for a new unit which can be provided with a positive or negative exponent and which can be combined with other unit symbols to form symbols for compound units. Note: because the name of the base unit kilogram already contains the SI prefix kilo, the names of decima! multiples and submultiples of the unit of mass are formed by adding appropriate prefixes to the word gram. Likewise, symbols for the

The multiple can usually be chosen so that the numerica! values

Table 3 Derived units

Quantity

Frequency Force Pressure, stress Energy, work, quantity of heat Power Electricity charge, quantity of electricity Electric potential, potential difference, electromoti ve force Electric capacitance Electric resistance Electric conductance Magnetic flux, flux of magnetic induction Magnetic flux density, magnetic induction lnductance Luminous flux Illuminance Activity (radioactive) Absorbed dose (of ionizing radiation)

will be between 0.1 and 1000, for example:

1.2Xl04 N canbewrittenas 12kN 0.003 94 m can be written as 3.94 mm 1401 Pa can be written as 1.401 kPa 3.1 X w-s s can be written as 31 ns

However, in a table of values for the same quantity or in a

Name of derived SI unit

hertz newton pascal joule watt coulomb voit farad ohm siemens weber tesla henry lumen lux becquerel gray

Symbol

Hz N Pa 1 w c V F Q s Wb T H lm lx Bq Gy

Expressed in terms of base or supplementary SI units or in terms of other

derived SI units

1 Hz = 1 s- 1

1 N = 1 kg m s-2

1 Pa= 1 N m-2

11=!Nm 1 W = 1 1 s-1

1C=1As 1 V = 1 1C = 1 W A-i 1 F = 1 cv-1

1 n = 1 vA-1

1 s = 1 n-1

1Wb=!VS 1 T = 1 Wb m-2

1 H= 1 Wb K 1

1 lm = 1 cd sr 1 lx = 1 lm m-2

1 Bq = 1 s-1

1 Gy = 1 1 kg-1

xxiv UNITS, SYMBOLS ANO CONVERSION FACTORS

Table 5 Units of practica! importance

Quantity Name of unit Unit symbol De finition

Time Minute min 1 min=60 s bour h 1 h=60 min day d ld=24h

plane angle degree 1 o= ('ITl/180) rad minute 1' = (1/60) 0

second 1" = (1160)' volume liter Il= l dm3

mass tonne lt=l03 kg

discussion of such values within a given context, it is generally better to use the same multiple for all items, even when some of the numerica! values will be outside the range 0.1-1000. For certain quantities in particular applications, the same multiple is customarily used throughout; for example the millimeter is used for dimensions in most engineering drawings.

It is recommended that only one prefix should be used in forming a multiple of a compound SI unit.

Errors in calculations can be avoided more easily if all values are expressed in SI units, prefixes being replaced by powers of 10.

Rules for writing unit symbols Unit symbols should be printed in roman (upright) type (irrespective of the type used in the rest of the text), should remain unaltered in the plural, should be written without a final full stop (period, point) and should be placed after the complete numerica! value in the expression for a quantity, leaving a clear space between the numerica! value and the unit symbol.

Unit symbols should be written in lowercase letters except that the first letter is written in upper case when the name of the unit is derived from a proper name. Example include:

m meter s second A ampere Wb weber

A compound unit formed by multiplication of two or more units may be indicated in one of the following ways:

N·m,N.m,Nm

Note that when using a unit symbol which coincides with the symbol for a prefix, special care should be taken to avoid confusion. The unit newton meter for torque should be written, for example, N mor m·N to avoid confusion with mN, the millinewton.

When a compound unit is formed by dividing one unit by another, this may be indicated in one of the following ways:

~. m/s or by writing the product of m and s- 1, for example as s ms-1.

In no case should more than one solidus (as in m/s) on the same line be included in such a combination unless parentheses are inserted to avoid ali ambiguity. In complicated cases, negative powers or parentheses should be used.

Non-SI units which may be used together with the SI units and their multiples

There are certain units outside the SI which are nevertheless recognized by the CIPM as having to be retained either because of their practica! importance (Table 5) or because of their use in specialized fields.

Prefixes given in Table 4 may be attached to many of the units given in Table 5; for example, milliter, ml; megaelectronvolt, MeV.

In a Jimited number of cases, compound units are formed with the units given in Table 5 together with SI units and their multiples; for example, kg/h; km/h.

Table 6 Basic units used in hydrology and water resources with conversion factors

Length

Are a

Volume

Velocity

Discharge (flow rate)

Density

Mass

Pressure (head of water)

1 m = 3.2808 ft l ft = 0.3048 m l in = 25.4 mm 1 mile = 1.6093 km 1 km = 0.6214 mile 1 mm = 0.0394 in l cm = 0.3937 in

l in2 = 645.2 mm2

1 ft2 = 0.0929 m2

1 mile2 = 2.590 km2

1 mile2 = 259 ha 1 acre = 4047 m2

1 acre = 0.4047 ha 1 ha = 2.4710 acres 1 km2 = 0.3861 mile2

1 cm2 = 0.1550 in2

1 m2 = 10.763 ft2

1 m3 = 10001 1 ft3 = 28.321 1 ft3 = 0.02832 m3

1 ft3 = 6.23 gal 1 ft3 = 7.4805 gal US 1 gal = 4.5461 1 gal = 0.00455 m3

1 gal = 0.1605 ft3

1 gal = 1.201 gal us 1 gal US = 3.78511 1 gal US = 0.003785 m3

1 cm3 = 0.06102 in3

1 acre-ft = 1233 m3

1 m s-1 = 3.2808 ft s-1

1 ft s-1 = 0.3048 m s-1

1 mile h-1 = 1.6093 km h-1

1 mile h-1 = 0.447 m s-1

1 m3 s-1 = 86.400 Mld 1 m3 s-1 = 35.3147 ft3 s-1

1 m3 s-1 = 19.00526 Mgd 1 Mld = O.Ql15 m3 s-1

1 Mld = 11.574 1 s-1

1 Mld = 0.22 Mgd 1 M1d = 0.26 Mgd US 1 ls-1 = 0.019 Mgd 1 Mgd = 4.546 Mld 1 Mgd = 0.0526 m3 s-1

1 Mgd = 52.616 1 s-1

1 Mgd = 4546 m3 d-1

1 ft3 s-1 = 0.0283 m3 s-1

1 ft3 s-1 = 28.32 1 s-1

1 Mgd US = 3785 m3 d-1

1 Mgd US = 0.0438 1 m3 s-1

1 ft3 s-1 mi1e-2 = 0.01094 m3 s-1 km-2

Water

1 lb 1 lb 1 ton 1 ton

1 mmHg

= 1000 kg m-3

= 453.6 g = 0.4536 kg

1016.05 kg 1.016 tonne

1.333 X 102 Pa

Gravitational acceleration (g) 9.807 m s-2 = 32.175 ft s-2

Temperature 9 (Fahrenheit temperature in °F) = S(Celsius temperature in °C) + 32

Temperature difference 9 (Temperature difference in °F) = 5(Temperature difference in oq

UNITS, SYMBOLS ANO CONVERSION FACTORS XXV

Table 7 Symbols, units and conversion factors (WMO)

II III IV V VI VII

Units Conversion

Item Element Symbol Recommended Also in use factor' Remarks

1 Acceleration due to gravity g m s-2 ft s-2 0.305 ISO 2 Albedo r Expressed as a decima! 3 Area ( cross-sectional) drainage bas in) A mz ft2 0.0929 ISO

km2 acre 0.00405 ISO ha 0.01 mile2 2.59

4 Chemical quality mg J-1 ppm -1 For dilute solutions 5 Chezy coefficient [ v(RhSt112] c m'/2 5-1 ft 112 s-1 0.552 ISO 6 Conveyance K m3 s-1 ftl s-1 0.0283 ISO 7 Degree day D degree day degree day Conversion Col. IV is based on oc

formula oc = 519 scale and Col. V on °F (°F- 32) scale

8 Density p kg m-3 Jb n-3 16.0185 ISO 9 Depth, diameter, thickness d m ft 0.305 ISO

cm in 2.54 10 Discharge (river ftow) (wells) Q m3 s-' ft3 s-' 0.0283 ISO

Qwe 1 s-1 gal (US) min-1 0.063 (unit area QA- 1, or partial) q m3 s-1 km2 ft3 s-1 mile-2 0.0109 ISO

1 s-1 km-2 10.9 11 Drawdown s m ft 0.305

cm 30.5 12 Dynamic viscosity, (absolute) 11 N s m-2 ISO

Pa, s, kg m-1 s-1 also in use

13 Evaporation E mm In 25.4 14 Evapotranspiration ET mrn in 25.4 15 Fraude number Fr Dimensionless number ISO 16 Head, elevation z m ft 0.305 ISO 17 Head, pressure hp m kg (force) cm-2 10.00

lb (force) in-2 0.705 18 Head, static (water level) h cm ft 30.05 ISO

m 0.305 = z + hp h

19 Head, total H m ft 0.305 ISO

20 =z+hp+hv Head, velocity hv cm ft 30.5

m 0.305 = v2(2gtl

21 Hydraulic conductivity (permeability) K cm s-1 m d-1 0.00116 ft min-1 0.508

22 Hydraulic diffusity = TL" 1 D cm2 s-1

23 Hydraulic radius = AP;;,1 Rh m ft 0.305 ISO 24 Ice thickness d. cm In 2.54 25 Infiltration !" mm In 25.4 26 Infiltration rate /f mm h-1 in h-1 25.4 27 Intrinsic permeability k 10-8 cm2 Darcy 0.987 28 Kinematic viscosity V mz s-1 ft2 s-1 0.0929 ISO 29 Length cm m 2.54 ISO

m ft 0.305 km mile 1.609

30 Manning's coefficient = R~13 S112 v-1 n s m-113 s ft-113 1.486 ISO lin = k roughness coefficient can also be used

31 Mass m kg lb 0.454 ISO g oz 28.35

32 Porosity n % cr. may also be used if needed

33 Precipitation p mm in 25.4 34 Precipitation intensity /p mm h-1 in h-1 25.4

xxvi UNJTS, SYMBOLS ANO CONVERSION FACTORS

Table 7 Continued

II III IV V VI

Units Conversion

Item Element Symbol Recommended Also in use factor'

35 Pressure p Pa hPa !00.0 mm Hg !33.3 in Hg 3386.0

36 Radiationb ( quantity of radiant energy R J m-2 ly 4.!86X 104

per unit area) 37 Radiation intensityb (flux per unit area) /R J m-2 s-I ly min- 1 697.6 38 Radius of influence r2 m ft 0.305 39 Recession coefficient c, Expressed as a decima! 40 Relative humidity (moisture) u % 4! Reynolds number Re Dimensionless number 42 Runoff R mm in 25.4 43 Sediment concentration c, kg m-3 ppm Depends on

density 44 Sediment discharge Q, t d-1 ton (US) d-1 0.907 45 Shear stress T Pa 46 Slope (hydraulic, basin) s Dimensionless number 47 Snow cover An % 48 Snow depth dn cm in 2.54 49 Snow melt M mm in 25.4

50 Soi! moisture u, %volume %mass Depends on density

5! Soi! moisture deficiency U' s mm in 25.4 52 Specific capacity = Qwe s-1 c, m2 s-I ft2 s- 1 0.0929 53 Specific conductance K J.LS cm-1

54 Specific yield Y, Expressed as decima! 55 Storage s m3 ft3 0.0283 56 Storage coefficient (groundwater) Cs Expressed as a decima! 57 Sunshine n/N Expressed as a decima!

58 Surface tension (J N m- 1

59 Temperature e oc oF Conversion formula oc = ~ (°F- 32)

60 Total dissolved solids 111d mg J-I ppm -1 61 Transmissi vity T mz d-I ft2 d-1 0.0929 62 Vapor pressure e Pa hPa 100.0

mmHg 133.3 3386.0

63 Velocity ( water) V m s-1 ft s-1 0.305 64 Volume V m3 ft3 0.0283

acre ft 1230.0 65 Water equivalent of snow w. mm in 25.4 66 Weber number we Dimensionless number 67 Wetted perimeter pw m ft 0.305 68 Width (cross-section, basin) b m ft 0.305

km mile 1.609 69 Wind speed u m s-1 km h-1 0.278

mile h- 1 0.447 k. (or kt) 0.514

70 Activity (amount of radioactivity) A Bq (Becquerel) Ci (Curie) 3.7 X 1010

71 Radiation fluence (or energy fluence) F 1 m-2 erg cm-2 103

72 Radiation flux intensity ( or energy flux 1 J m-2 s-I erg cm-2 s-1 103

intensity)

NOTE: Where international symbols exist these have been used where appropriate and are indicated as ISO in the last column. 'Col. IV = Conversion factor (Col. VI) X Col. V.

VII

Remarks

See also Head, pressure

ISO

ISO ISO

Normally expressed as daily

at e = 25°C

Actual (n)/possible (N) hours ISO ISO t also in use

For dilute solutions

ISO ISO

ISO

IAEA IA EA IA EA

b General terms. For detailed terminology and symbols see the WMO Guide to Meterological Instruments and Metlwds of Observation (WMO) No. 8).

UNITS, SYMBOLS ANO CONVERSION FACTORS xxvii

Definitions of SI base units and supplementary units

Base units

Metre The meter is the length equal to 1 650 763.73 wavelengths in vacuum of the radiation corresponding to the transition between the levels 2p 10 and 5d5 of the 86K.r atom.

Kilogram The kilogram is the unit of mass; it is equal to the mass of the international prototype of the kilogram.

Second The second is the duration of 9 192 631 770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the mcs atom.

Ampere The ampere is that constant current which, if maintained in two straight parallel conductors of infinite length, of negligible circular cross-section, and placed 1 meter apart in vacuum, would produce between these conductors a force equal to 2 X 10-7 newton per meter of length.

Kelvin The kelvin, unit of thermodynamic temperature, is the fraction 1/273.16 of the thermodynamic temperature of the triple point of water.

The Thirteenth CGPM (1967, Resolution 3) a!so decided that the kelvin and its symbol K should be used to express an interval or a difference of temperature. In addition to the thermodynamic tem­perature (symbol T) expressed in kelvins, use is also made of Celsius temperature (symbol t) defined by the equation t = T- T" where T0 = 273.15 K by definition.

The Celsius temperature is in general expressed in degrees Celsius (symbol "C). The unit 'degree Celsius' is thus equal to the unit 'kelvin' and an interval or a difference of Celsius temperature may also be expressed in degrees Celsius.

Mole The mole is the amount of substance of a system which contains as many elementary entities as there are atoms in 0.012 kilogram of 12C. When the mole is used, the elementary entities must be specified and may be atoms, molecules, ions, electrons, other particles/or specified groups of such particles.

Candela The candela is the luminous intensity, in the perpendicular direction, of a surface of 1/600 000 square meter of a black body at the tempera ture of freezing platinum under a pressure of 101 325 newtons per square meter.

Supplementary units

Radian The radian is the angle between two radii of a circle which cut off on the circumference an arc equal in length to the radius.

Steradian The steradian is the solid angle which, having its vertex in the center of a sphere, cuts off an area of the surface of the sphere equal to that of a square with sides of length equal to the radius of the sphere.

Units used in hydrology and water resources

Table 6 Iists the basic units used in hydrology and water resources, together with conversion factors.

Table 8 Misce/laneous symbols

Item Element Symbol Remarks

Concentration c ISO 2 Coefficient (in general) c ISO 3 Difference ~ ISO, values expressed in

same units 4 Inftow 1 5 Lag time ~~ Various units 6 Load L 7 Number of (or rank) 111 ISO 8 Outftow o 9 Recharge f See Infiltration in Table 7

10 Total number N

Table 9 Recommended units appearing in Table 7

Item Element Symbol Remarks

1 centimeter cm ISO 2 day d ISO 3 degree Celsius "C ISO 4 gram g ISO 5 hectare ha 6 hectopascal hPa ISO 7 hour h ISO 8 joule J ISO 9 kilogram kg ISO

10 kilometer km ISO Il knot kn, kt 12 liter 1 ISO 13 meter m ISO 14 microsiemens J.LS 15 milligram mg ISO 16 millimeter mm ISO 17 minute min ISO 18 newton N ISO 19 parts per million ppm 20 pascal Pa ISO 21 percentage % 22 second ISO 23 tonne (metric ton) ISO 24 year a ISO 25 bequerel Bq IAEA

Recommended symbols, units and conversion factors Table 7 lists symbols, units and conversion factors recommended by the WMO. Table 8, lists some miscellaneous symbols and Table 9 gives the recommended units appearing in Table 7.

Source World Meteorologica! Organization, 1994. Guide to Hydrological

Practices, 5th edn. WMO, Geneva.

Bibliography BS 5555, 1993. SI Units. British Standards Institution, London. Herschy, R.W., 1995. Streamjlow Measurement, Chapman & Hali,

London. ISO 1000, 1992 SI units.