Stream HydrologyAn Introduction for EcologistsSecond EditionNancy D. GordonThomas A. McMahonBrian L. FinlaysonCentre for Environmental Applied Hydrology,The University of MelbourneChristopher J. GippelFluvial Systems Pty LtdRory J. NathanSinclair Knight Merz Pty LtdStream HydrologyStream HydrologyAn Introduction for EcologistsSecond EditionNancy D. GordonThomas A. McMahonBrian L. FinlaysonCentre for Environmental Applied Hydrology,The University of MelbourneChristopher J. GippelFluvial Systems Pty LtdRory J. NathanSinclair Knight Merz Pty LtdCopyright # 2004 John Wiley & Sons Ltd, The Atrium, Southern Gate, Chichester,West Sussex PO19 8SQ, EnglandTelephone (+44) 1243 779777Email (for orders and customer service enquiries): cs-books@wiley.co.ukVisit our Home Page on www.wileyeurope.com or www.wiley.comAll Rights Reserved. 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If professional advice or other expertassistance is required, the services of a competent professional should be sought.Other Wiley Editorial OfcesJohn Wiley & Sons Inc., 111 River Street, Hoboken, NJ 07030, USAJossey-Bass, 989 Market Street, San Francisco, CA 94103-1741, USAWiley-VCH Verlag GmbH, Boschstr. 12, D-69469 Weinheim, GermanyJohn Wiley & Sons Australia Ltd, 33 Park Road, Milton, Queensland 4064, AustraliaJohn Wiley & Sons (Asia) Pte Ltd, 2 Clementi Loop #02-01, Jin Xing Distripark, Singapore 129809John Wiley & Sons Canada Ltd, 22 Worcester Road, Etobicoke, Ontario, Canada M9W 1L1Wiley also publishes its books in a variety of electronic formats. Some content that appears in print may not be available in electronicbooks.Library of Congress Cataloging-in-Publication Data:Stream hydrology : an introduction for ecologists / by Nancy D. Gordon ... [et al.]. 2nd ed.p. cm.Rev. ed. of: Stream hydrology / Nancy D. Gordon, Thomas A. McMahon, Brian L. Finlayson. c 1992.Includes bibliographical references and index.ISBN 0-470-84357-8 (cloth : alk. paper) ISBN 0-470-84358-6 (pbk. : alk. paper)1. Rivers. 2. Hydrology. 3. Stream ecology. I. Gordon, Nancy D. Stream hydrology.GB1205.G65 2004551.48/3dc22 2004005074British Library Cataloguing in Publication DataA catalogue record for this book is available from the British LibraryISBN 0-470-84357-8 (HB)ISBN 0-470-84358-6 (PB)Typeset in 9/11pt Times by Thomson Press (India) Limited, New DelhiPrinted and bound in Great Britain by Antony Rowe Ltd, Chippenham, WiltshireThis book is printed on acid-free paper responsibly manufactured from sustainable forestry in which at least two trees are plantedfor each one used for paper production.ContentsPreface to the Second Edition xiPreface to the First Edition xiii1 Introducing the Medium 11.1 Water as a Fluid 11.2 The Physics of Fluids 11.3 Physical Properties of Water 31.3.1 Density and Related Measures 31.3.2 Viscosity and the No-slip Condition 51.3.3 Surface Tension 51.3.4 Thermal Properties 71.3.5 Entrained Air and Dissolved Oxygen 82 How to Study a Stream 112.1 Focusing on Physical Habitat 112.2 The Planning Process 162.2.1 General 162.2.2 What Is the Question? 172.2.3 Choosing Your Method: The Study Design 172.2.4 Collecting Information: The Value of a Pilot Study 182.2.5 Analysing and Presenting the Results 182.3 Strategic Sampling 192.3.1 Population, Sample and Other Vocabulary of the Trade 192.3.2 The Errors of Our Ways 202.3.3 Considerations in Choosing a Sampling Design 212.3.4 Partitioning the Stream 222.3.5 Basic Sampling Designs 232.3.6 Sample Size 272.4 Know Your Limitations 272.5 Examples of How and How Not to Conduct a Study (by M. Keough) 283 Potential Sources of Data (How to Avoid Reinventing the Weir) 313.1 Data Types 313.2 Physical Data Sources, Format and Quality 313.2.1 Where to Look for Data and What You Are Likely to Find 313.2.2 Data Quality 333.2.3 How to Fill in a Streamow Record 363.3 Maps: Finding Those Spatial Places 373.3.1 What Types of Maps Are Useful? 373.3.2 Map Interpretation 413.3.3 Revision, Accuracy and Standardization of Maps 433.4 Photographs and Other Remotely Sensed Data 433.4.1 What Is Remote Sensing? 433.4.2 Photographs 443.4.3 Other Remote Sensing Imagery 453.4.4 Sources of Imagery 463.4.5 Interpretation, Classication and Ground Truthing of Imagery 474 Getting to Know Your Stream 494.1 General Character 494.1.1 Preliminary Introductions 494.1.2 Putting the Stream Channel and Its Catchment into Context 494.1.3 Initial Assessments of the State of a Stream 504.1.4 An Example of a River Condition Survey: The Index of Stream Condition, Victoria, Australia 544.2 Catchment Characteristics 564.2.1 General 564.2.2 Delimiting and Measuring the Catchment Area 564.2.3 Stream Length 584.2.4 Stream Patterns 594.2.5 Stream Orders 614.2.6 Miscellaneous Morphometric Measures 634.3 Streamow Hydrographs 654.3.1 Denitions 654.3.2 Hydrograph Separation 664.3.3 Factors Inuencing the Hydrograph Shape 674.3.4 Recession Curve Analysis 684.4 How Does This Stream Measure Up? 684.4.1 General 684.4.2 Annual Statistics 694.4.3 Monthly Statistics 714.4.4 Daily Statistics 714.4.5 A Method for Describing Hydrological Predictability: Colwells Indices 715 How to Have a Field Day and Still Collect Some Useful Information 755.1 Venturing into the Field 755.2 Surveying: A Brief Introduction 765.2.1 General 765.2.2 Horizontal Distance 765.2.3 Vertical Distance 775.2.4 Slope 785.2.5 The Full Contingent of Co-ordinates, Including Methods of Mapping 795.3 Methods of Measuring Areal Extent 845.3.1 General 845.3.2 Visual Estimation of Percentage Cover 845.3.3 Point Intercept Method 845.3.4 Line Intercept Method 855.3.5 Grids 875.4 Surveying Streams 875.4.1 General 875.4.2 Cross-sectional Proles 875.4.3 Channel Slope and Thalweg Prole 885.4.4 Bed Surface Materials 895.4.5 Mapping the Stream Reach 89vi Contents5.5 Measurement of Water Level or Stage 905.5.1 General 905.5.2 The Staff Gauge 905.5.3 Maximum Stage Recorders or Crest Gauges 905.5.4 Automatic Recorders 905.5.5 Depth to the Water Table: Piezometry 915.6 Measurement of Discharge (Streamow) 925.6.1 General 925.6.2 Volumetric Measurement 925.6.3 Velocity-area Method 935.6.4 Dilution Gauging Methods 965.6.5 Stream Gauging 985.6.6 Slope-area Method of Estimating Discharge 1015.7 Substrates and Sediments: Sampling and Monitoring Methods 1045.7.1 General 1045.7.2 Bank Material Sampling (Soil Sampling) 1055.7.3 Bed Material Sampling 1055.7.4 Sampling Suspended Sediments 1065.7.5 Sampling Bedload Sediments 1105.7.6 Erosion and Scour 1135.8 Substrates and Sediments: Analysis of Physical Properties 1145.8.1 General 1145.8.2 Soil Moisture Content, Gravimetric Method 1145.8.3 Sediment Concentration 1145.8.4 Particle Size 1155.8.5 Presentation of Particle Size Data 1195.8.6 Particle Shape: Roundness, Sphericity 1215.8.7 Particle Arrangement and Other Miscellaneous Bulk Properties 1225.9 Water Quality 1256 Water at Rest and in Motion 1276.1 General 1276.2 Hydrostatics: the Restful Nature of Water 1276.2.1 Pressure 1276.2.2 Buoyancy 1296.3 Studying the Flow of Fluids 1306.3.1 Steady and Unsteady Flow 1306.3.2 Streamlines 1306.3.3 Conserving Mass: The Principle of Continuity 1316.3.4 Energy Relationships and the Bernoulli Equation 1316.4 Narrowing the Focus: Flow of a Viscous Fluid 1326.4.1 Laminar and Turbulent Flow 1326.4.2 Flow Past Solid Surfaces: The Boundary Layer 1366.5 The Microenvironment: Flow Near Solid Surfaces 1416.5.1 General 1416.5.2 Describing the Velocity Prole and Boundary Layer Thickness near a Solid Surface 1416.5.3 Shear Stress and Drag Forces 1436.5.4 Flow around Bluff Bodies 1466.5.5 Lift 1526.5.6 Methods of Microvelocity Measurement 1536.6 Open-channel Hydraulics: The Macro-environment 1556.6.1 But First, A Few Denitions 155Contents vii6.6.2 Introduction to Hydraulics 1556.6.3 The Variations of Velocity in Natural Channels 1566.6.4 Energy Relationships in Streams 1596.6.5 Shear Stress and the Uniform Flow Equations of Chezy and Manning 1636.6.6 Water-surface Proles in Gradually Varied Flow 1656.6.7 Hydraulic Jumps and Drops, Alias Rapidly Varied Flow 1677 Its Sedimentary, Watson! 1697.1 Introduction to Stream Channels, Streambeds and Transported Materials 1697.1.1 General 1697.1.2 Making Up a Channel Bed 1697.1.3 What Sort of Debris Is Transported? 1707.1.4 Sediment Distribution and Discharge 1727.1.5 Ecological Implications 1737.2 Stream-shaping Processes 1747.2.1 A Note about Stream Power 1747.2.2 Adjustments and Equilibrium 1767.2.3 Balancing Slope, Streamow, and Sediment Size and Load 1777.2.4 Floods and Floodplain Formation 1787.2.5 Channel-forming Discharges 1797.2.6 Fluvial Geometry 1807.3 The Ins and Outs of Channel Topography 1827.3.1 Channel Patterns 1827.3.2 Pools, Rifes and Steps 1857.3.3 Bars 1867.3.4 Dunes, Ripples and Flat Beds of Sand 1877.4 Sediment Motion 1897.4.1 Erosion, Transport and Deposition 1897.4.2 Deviations from Ideal 1907.4.3 Predicting a Particles Get Up and Go 1917.5 Sediment Yield from a Catchment 1957.5.1 Sediment Sources and Sinks 1957.5.2 Sediment Yield Variations 1977.5.3 Computing Sediment Discharge and Yield from Measured Concentrations 1987.5.4 The Estimation of Sediment Discharge from Streamow 1998 Dissecting Data with a Statistical Scope 2018.1 Introduction 2018.1.1 General 2018.1.2 Floods and Droughts 2018.1.3 Data Considerations 2038.1.4 Putting Statistics into a Proper Perspective 2038.2 Streamow Frequency Analysis 2048.2.1 General Concepts 2048.2.2 Probability and Average Recurrence Intervals 2048.2.3 The Data Series 2058.2.4 Graphical Methods: The Probability Plot 2078.2.5 Fitting Probability Distributions 2088.2.6 A Few Good Probability Distributions 2108.2.7 Zeros and How to Treat Them 2128.2.8 Goodness, The Distribution Fits! 2148.2.9 Interpreting Frequency Curves 214viii Contents8.3 Flow-duration Curves 2158.3.1 General 2158.3.2 Constructing Flow-duration Curves 2168.3.3 Interpretation and Indices 2178.4 Flow Spell Analysis 2188.5 Extrapolating from the Known to the Unknown 2198.5.1 General 2198.5.2 Transposing Data from Gauging Stations to Less-endowed Sites 2208.5.3 Regionalization 2218.6 Numerical Taxonomy: Multivariate Analysis Techniques 2248.6.1 General 2248.6.2 Similarity/Dissimilarity Indices 2258.6.3 Ordination 2258.6.4 Classication 2288.6.5 Other Sources of Information on Numerical Taxonomy 2319 Putting It All Together: Assessing Stream Health, Stream Classication,Environmental Flows and Rehabilitation 2339.1 Putting Theories into Practice 2339.2 Understanding Stream Values 2379.2.1 What Are Stream Values? 2379.2.2 Ecological Potential 2379.2.3 The Role of Science in the Stream Health Policy Debate 2389.3 Assessing Stream Health 2399.3.1 Introduction 2399.3.2 Describing Reach Condition 2409.3.3 Physico-chemical Assessment 2419.3.4 Habitat Assessment 2429.3.5 Hydrological Assessment 2479.3.6 Bioassessment 2499.3.7 Types of Stream Health Monitoring Program 2619.3.8 Selecting a Method for Measuring Stream Health 2619.4 The Use of Stream Classication in Management 2629.4.1 Introduction 2629.4.2 Ecological Classication Models Based on Energetics, Structure, Function andDynamics of Rivers 2639.4.3 Geomorphological Classication Models Based on River Process and Structure 2679.4.4 Hydrologically Based Classication 2739.4.5 Water Quality-based Classication 2759.4.6 Combined Physical-chemical-ecological Classication Models 2769.4.7 Ecoregions and Multi-scale Classication 2779.4.8 Wetland Classication 2789.4.9 Estuary Classication 2819.4.10 Classication of Conservation Value of Rivers 2829.4.11 Designated Use Classication 2839.4.12 Summary 2869.5 Assessing Instream Environmental Flows 2869.5.1 Introduction 2869.5.2 Instream and Environmental Flows Dened 2879.5.3 Three Basic Assumptions of Environmental Flows Assessment 2889.5.4 Forms of Environmental Flow Assessment 2909.5.5 Hydrological Methods 291Contents ix9.5.6 Hydraulic Rating Methods 2939.5.7 Habitat Rating Methods 2959.5.8 Holistic Methods 2999.5.9 Other Approaches 3029.5.10 Implementation and Evaluation of Environmental Flows 3129.5.11 Summary 3189.6 Stream Rehabilitation 3199.6.1 The Basis of Stream Rehabilitation 3199.6.2 Addressing Biotic Factors 3269.6.3 Correction of Physical Limiting Factors 3309.6.4 Rehabilitation of Channel Form 3339.6.5 Instream Habitat Improvement Structures 3459.6.6 Evaluation of a Range of Stream Rehabilitation Projects 3499.6.7 Some Reections on Stream Rehabilitation 357Appendix Basic Statistics 359References 371Index 423x ContentsPreface to the Second EditionOne of the main purposes in writing the rst edition of thisbook in 1992 was to help improve communication bet-ween the disciplines of streamecology andriver engineeringand to foster a sense of co-operation in these interdisci-plinary efforts. We would like to think that we played apart, however small, in assisting the tremendous growth ininterdisciplinary and multidisciplinary research and appli-cation that followed over the next decade. But thisphenomenon was inevitable anyway; academics, policymakers andmanagers alike hadrecognisedthat river manage-ment could not take the next step forward unless thevarious experts got together and problems were assessedand solved from a broad perspective. An engineer, geomor-phologist and ecologist will still have a different emphasiswhen conceptualising a stream, but these days each view-point is cognisant of, and is informed by, the others.This second edition was a long time in its gestation. Theeld of river research and management has been evolvingso rapidly that it was difcult for us to decide when was anappropriate time to update the book. The backgroundinformation did not present a real problem, as most of itis grounded in long established principles of hydrologyand uid mechanics. However, the real growth area was inthe application of science to stream management; the trialand error approach is no longer acceptable. We feel thatnow is a good time to take stock of these developments.Many countries have implemented new river laws thatrequire managers to at least maintain the current levels ofstream health and be highly accountable for their actions.The ecosystem concept, which originated in ecology as aresearch paradigm, has now been transferred to the realmof public policy; physico-chemical characteristics are stillimportant, but we now speak of stream health andmeasure it in terms of water quality, habitat availabilityand suitability, energy sources, hydrology, and the biotathemselves. Introduction of the European Union WaterFramework Directive in December 2000 has already led towidespread changes in assessment of stream health inEurope. Stream classication is now a routine rst stepthat simplies the inherent complexity of stream systems,helping to facilitate many aspects of the managementprocess. Research has clearly established the impacts ofow regulation, and the last decade has seen considerablegrowth in research and assessment of environmental owneeds. River rehabilitation is now one of the central themesof the river management industry. One of our objectives inwriting this second edition is to bring some methodologi-cal order to these developments. Another objective is tocritically evaluate the level of success and failure in effortsto rehabilitate streams. This could not have been done inthe rst edition, because sofewexamples existed at that time.In this second edition we maintain an emphasis on thephysical environment. Information has been drawn fromthe elds of geomorphology, hydrology and uid mechanics,with examples given to highlight the information ofbiological relevance. Chapters 18, which include toolsfor studying and describing streams, have been updated bythe original authors. Chapter 9, which reviews rivermanagement applications, has been totally re-written byDr. Chris Gippel of Fluvial Systems Pty Ltd. In this nalchapter, we could not avoid venturing a little further intothe biological realm, and we also drew on a much widerrange of source material. Readers expecting mathematicalderivations will still be disappointed; we concentrate onpresenting principles and demonstrating their practicaluse.The software package, AQUAPAK (readers of the rstedition will be familiar with the original version) has beencompletely updated by the original author Dr Rory Nathanof Sinclair Knight Merz Pty Ltd. AQUAPAK can bedownloaded at http://www.skmconsulting.com/aquapakand runs in Windows. AQUAPAK has been tailor madefor the readers of this book and assumes no prior knowl-edge on the part of the user other than basic computerkeyboard skills. More advanced users may wish toinvestigate the Catchment Modelling Toolkit availableon-line from the Cooperative Research Centre for Catch-ment Hydrology at http://www.toolkit.net.au/cgi-bin/WebObjects/toolkit.It is clear now that many mistakes have been made instream management in the past, leading to what we nowcall stream degradation. This is a retrospective view,because at the time, river managers were acting underthe impression that their work would improve the value ofthe river from the perspective of the prevailing dominantsocial view. Other failed works were simply ill-informedfrom the technical perspective. Streams are now managedfor a wider range of values, and advances made in streammanagement technology certainly hold the promise ofecologically healthier and economically more valuablestreams for the future. But we have to remember thatstream management is far from simple, and an ill-informed approach, regardless of the best intentions, canfail to produce the expected outcomes. So, as well aslearning more about river processes, developing methodsfor rehabilitation and playing a leading role in implement-ing science-based management, river professionals have aresponsibility to provide honest evaluations of the relativesuccess of works. New knowledge so generated can thenbe used to improve the next generation of river manage-ment. At one extreme some may still hold the view thatfundamental science does not have much of a role to playin the practical domain of the on-ground river manager,while at the other extreme, some researchers mightstill be content to explore rivers with little thought aboutthe implications of how the new knowledge might assistpractical management or policy development. We hopethat this book provides a resource and inspiration to fellowriver management professionals, academics and studentswhose outlook and passion lies some where between, orwho are working to bridge these perspectives.Web sites referenced in the book are current as of thedate of publication but may be subject to change in thefuture. Any mention of commercial web sites does notconstitute endorsement of a product.ACKNOWLEDGEMENTSThe authors would like to express appreciation to anumber of individuals for their contributions during theevolution of this text. Mr. Andrew Douch created many ofthe original drawings and diagrams for Chapters 46 in therst edition. The diagrams in this edition were re-drawn ornewly prepared by Chandra Jayasuriya and Fatima Basicof the School of Anthropology, Geography and Environ-mental Studies, the University of Melbourne. We aregrateful to Dr Michael Keough of the Department ofZoology, University of Melbourne, for producing therealistic examples of Section 2.5. Many individuals,listed in the rst edition, provided general guidance andreviews of draft materials that helped focus the scope ofthe book and greatly added to its accuracy and applic-ability. Their assistance is again acknowledged. Severalreviewers provided suggestions for improvement whichadded to the quality of this second edition.We are very appreciative of the professionalism andhelpfulness of the people at John Wiley & Sons, especiallySally Wilkinson, Keily Larkin and Susan Barclay and tothe team of Thomson Press (India) Ltd.Jyoti Narula,Sanjay Jaiswal, M.S. Junaidi, C.P. Kushwaha and UdayanGhoshwho greatly contributed to the quality of the nalproduct.The work which led to the production of the rst editionof this book was supported by funds provided by the thenAustralian Water Research Advisory Council, now Landand Water Australia.COPYRIGHTED MATERIALSWe are grateful to the following organizations, individualsand publishers for permission to reproduce copyrightedmaterial(s):Addison Wesley, Alberta Environment, American Asso-ciation of Petroleum Geologists, American FisheriesSociety, American Geophysical Union, American Societyof Civil Engineers (ASCE), American Water ResourcesAssociation, ANZECC, Birkhauser Verlag AG, BlackwellScience, British Columbia Forest Service, Butterworth-Heinemann, Canadian Water Resources Association,Carfax Publishing Ltd., Colorado State University, Crown(State of Victoria), CSIRO Publishing, Department ofPrimary Industries, Geological Survey of Victoria, Depart-ment of Sustainability and Environment, Department ofthe Environment and Heritage, Diputacio de Barcelona,East Gippsland Catchment Management Authority,Elsevier, EPA, Federal Environmental Agency, FreshwaterResearch Unit, Geological Society of America, Harper-Collins Publishers, Hodder and Stoughton, HoughtonMifin Company, Institution of Engineers, John Wiley& Sons Ltd., John Wiley & Sons Inc., Land and WaterAustralia, Macmillan, McGraw-Hill, Michigan Depart-ment of Natural Resources, National Park Service, NRCResearch Press, NSW Department of Infrastructure, Plan-ning and Natural Resources, Ontario Ministry of NaturalResources, Oxford University Press, P. Cardiyaletta, Pear-son, Pollution Control Department, Princeton UniversityPress, Rellim Technical Publications, R. L. Folk, RoyalSociety for the Protection of Birds, Scottish EnvironmentProtection Agency, SEPM Society for Sedimentary Geol-ogy, Springer-Verlag GmbH & Co. KG, Stanley Schumm,Swedish Environmental Protection Agency, Texas WaterDevelopment Board, The Living Murray, The RoyalSociety of New Zealand, The University of Melbourne,UNEP, UNESCO, USDA, U.S. Army Corps of Engineers,U.S. Federal Interagency Subcommittee on Sedimen-tation, U.S. Fish and Wildlife, USGS, Van NostrandReinhold International, Washington Department ofEcology, Water Resources Publications, LLC, WaterStudies Centre, Wildlands Hydrology, WHO, WorldMeteorological Organisation, Worldbank.xii Preface to the Second EditionPreface to the First EditionIn interdisciplinary applications of stream hydrology,biologists and engineers interact in the solution of anumber of problems such as the rehabilitation of streams,the design of operating procedures and shways for dams,the classication of streams for environmental valuesand the simulation of eld hydraulic characteristics inlaboratory umes to study ow patterns around obstaclesand organisms. One of the main purposes in writing thisbook was to help improve communication between thetwo disciplines and foster a sense of co-operation in theseinterdisciplinary efforts.On the surface, the denitions of ecology and hydrol-ogy sound very similar: ecology is the study of theinterrelationships between organisms and their environ-ment and with each other, and hydrology is the study ofthe interrelationships and interactions between water andits environment in the hydrological cycle. In general,ecology is a more descriptive and experimental scienceand hydrology is more predictive and analytical. Thisfundamental difference inuences the way streams arestudied and perceived in the two disciplines.For example, a diagram of an ecologists view of astream might appear as follows:Here, the focus is on the aquatic biota, their interrela-tions, and the physical and chemical factors which affectthem. An engineering hydrologist, on the other hand,might view the same stream much differently, perhapsmore like this:In this image, the physical dimensions of the streamhave been simplied into a few numbers from whichestimates can be made of how the stream will respondunder different ow conditions.Neither view is superior to the other; each representsonly a fraction of all there is to know about the stream.Interdisciplinary interaction offers a way of merging theinformation contained in the different views into a morecomplete picture. It is often at the interface betweendisciplines, in fact, that new ideas are generated andprogress is made. Perhaps like a stereo pair, new dimen-sions will be revealed when the images are successfullysuperimposed.The emphasis of this text is on the physical environ-ment. Information has been drawn from the elds ofgeomorphology, hydrology and uid mechanics, withexamples given to highlight the information of biologicalrelevance. Mathematical derivations have been omitted;instead, the intent was to provide an intuitive understand-ing of the principles, demonstrate their practical use andleave the mathematics to a computer. A software package,AQUAPAK, has been provided for this purpose. Omissionsand simplications were necessary in conveying the widerange of subject matter. We can only resort to the blanketstatement that everything is more complicated than ourdescription of it, and that ours is merely another view ofstreams.A practical approach has been taken, with the chapteron eld techniques forming a central part of the text. Inother chapters, examples have been given so that theprinciples can be applied more readily. Field studies inthe Acheron River Basin, located approximately 100 kmto the east of Melbourne, provided information for# benthic macro- invertebrates = 10 000/m2 pH = 7.2 TDS = 220 mg/l DO = 8.3 mg/l1V = 0.4 m/sA = 2.5 m2n = 0.08 = 125 N/m25examples throughout the book. We did this to maintaincontinuity, as well as to illustrate how we went aboutgetting to know this river system.The process of getting to know a stream is not unlikethat of a doctor learning about a patient and his or herhealth. A conscientious doctor will look beyond thecharts, images and the results of various tests to obtain asense of what causes the patients health to be what it is.In the same manner, hydrological data, aerial photographs,channel surveys and water quality analyses only measuresymptoms of a streams condition, and, as with humanhealth, the underlying causes are complex and nebulous.Just as patients are more than the sum of their con-nective tissues and blood vessels, streams, too, should beviewed holistically as a continuum from source to seaand as systems which interact with the surroundingenvironment. This book presents methods for diagnosingthe physical condition of streams. Criteria for establishingwhat constitutes physical health are yet to be developed.As Leopold (1960) advocated over 30 years ago, bench-mark stations free from grazing and other human inu-ences are needed in order to evaluate the effects ofhumans on ecologic and geologic change. Interdisciplin-ary studies are essential for establishing these baselineconditions, for determining the sensitivity of a givenstream to stress and for developing appropriate rehabi-litation procedures to cure those streams which arefound to be in poor condition.xiv Preface to the First Edition1Introducing the Medium1.1 Water as a FluidWater is a widespread, life-sustaining substance, compris-ing some 5090% of living materials and covering nearlythree-fourths of the Earths surface. Of the Earths totalmoisture, however, about 97% is contained in the oceansand less than 0.0002% ows through its rivers andstreams. Water is recycled globally, with the relative pro-portions of ice, water vapour, fresh water and salt waterchanging as the earth warms and cools. Scientists formerlybelieved that the total amount of water on Earth wasessentially constant, but new evidence points to a smallinux of water from snowball comets (Pielou, 1998).Water is a substance with many unique chemical andphysical properties. Unlike most substances that contractwhen frozen, water expands, allowing ice to oat on thesurfaces of lakes and streams. It is found as a liquid attemperatures common to most places on Earth. With itsgreat heat capacity it can absorb or lose a large amount ofenergy before showing a change in temperature. As auniversal solvent, it dissolves gases, nutrients and miner-als. Its internal cohesion gives rise to surface tension, whichallows water striders to traverse a pools surface or evenrun upstream. Because of its physical properties, a quitedifferent set of environmental conditions is presented toamoebae and sh that both live in the same waters.Depending on the temperature, water can exist as eithera liquid, a gas (water vapour) or a solid (ice). Combina-tions such as steam-air mixtures or water with entrainedair fall into a specialized category called two-phase ows.The general term uid describes both gases and liquids,examples being oxygen, motor oil, liquid glass andmercury. The differences between uids and solids arenot always obvious. Fluids ow readily under the slightestof forces; they do not have a denite shape and vesselsare required to contain them. Solids are substances that areconsidered to have both a denite volume and a deniteshape. Thus, the line is drawn between molasses as a uidand gelatin as a solid.Liquids are distinguished from gases by their cohesive-ness. Whether sitting in a laboratory beaker or in a frogpond, a liquid will have a denite volume. It will also havea free surface, which is horizontal when the uid is at rest.A gas, in contrast, does not have a denite volume, andwill expand to ll a container enclosing it.The next section will introduce some basic principles ofphysics and the system of units used in the text. Theseconcepts are applied to the description of physical pro-perties of water in Section 1.3.1.2 The Physics of FluidsThe properties and motion of a uid, such as water, aremeasured in terms of four basic quantities: mass, length,time and temperature. The magnitudes of these quantities(e.g. how hot or how large) are expressed in units. In theInternational System of Units (SI), the fundamental orbase units are given asv kilogram (kg)mass,v metre (m)length,v second (s)time,v Kelvin (K)temperature.In studies of aquatic systems, absolute temperatures arenot normally of interest, and for the purposes of this text,temperature will be expressed in C (Celsius), where273.15 K=0 C, and a change of 1 C is the same as achange of 1 K.The metre was originally proposed as 107of the lengthof the meridian through Paris (Blackman, 1969). It is nowdened in terms of the wavelength of a specic type oforange light. The unit of time, the second, is dened byStream Hydrology: An Introduction for Ecologists, Second Edition.Nancy D. Gordon, Thomas A. McMahon, Brian L. Finlayson, Christopher J. Gippel, Rory J. Nathan#2004 John Wiley & Sons, Ltd ISBNs: 0-470-84357-8 (HB); 0-470-84358-6 (PB)an atomic standard based on caesium. The unit of masswas originally based on the mass of a certain volume ofwater at prescribed conditions. Thus, conveniently, a litre(0.001 m3) of water at 4 C has a mass of about 1 kg.Whereas these base units are all dened in reference tosome standard, there are other quantities, such as velocity,for which standards are impractical. These quantities haveunits that are dened in terms of the base units and arethus called derived units. Some of the quantities asso-ciated with the area of physics known as mechanics,which are relevant to the study of water, will be discussed.A summary of both fundamental and derived units, theirdimensions and associated symbols, is given in Table 1.1.For tables of conversion factors and other informationrelevant to water resource studies, Van Haverens (1986)handbook is a highly useful reference.VelocityMotion is dened as a change of position. Speed refersto the rate at which the position changes with time, i.e.if a raft oats 500 m downstream in 5.5 min, then itsaverage speed is about 1.5 m/s. Technically, velocity refersto the speed in a given direction; however, in ordinaryspeech, no distinction is usually made between velocityand speed.Discharge or StreamowDischarge, or streamow, is the rate at which a volume ofwater ows past a point over some unit of time. In the SIsystem it is expressed in metres cubed per second (m3/s).For example, if a small spring lled a 0.01 m3bucket in2 s, its discharge would be 0.005 m3/s. Discharge is nor-mally symbolized by Q.AccelerationAcceleration is the rate at which velocity changes withtime. An object dropped off a cliff on Earth will accelerateat 9.807 m/s2(this gravitational acceleration (g) variesslightly with position on the Earths surface). The distanceh covered by a dropped object (starting at zero velocity) ish = 12gt2(1.1)where t is the time in seconds from when it was droppedand h is in metres.ForceForce is described in terms of its effects. It may cause anobject to change its direction of motion, to stop or start, torise or fall. By Newtons second law of motion, force isproportional to mass multiplied by acceleration. In the SITable 1.1. Common quantities used in the description of uids. Adapted from Vogel, Steven; Life in Moving Fluids. #1981 byWillard Grant Press, 1994 revised Princeton University Press. Reprinted by permission of Princeton University Press2 Stream Hydrology: An Introduction for Ecologists[Text not available in this electronic edition.]system, the unit of force is the Newton (N), dened as theforce necessary to accelerate 1 kg at 1 m/s2:Force (N) = Mass (kg) acceleration (ms2) (1.2)A very small Newtons apple with a mass of 0.102 kgexperiences a gravitational force on Earth of about 1 N.The term weight does not appear in the SI system, andcan create confusion particularly when converting fromthe Imperial to the SI system. Mass is an expression of theamount of matter in something, whether a brick, a balloonor a bucket of water. Weight is a gravitational force. IfNewtons apple were taken to the moon, it would still havea mass of 0.102 kg, but its weight (the force due togravity) would be considerably reduced. On Earth, if anAmerican buys 2.2 pounds (lb) of apples at the super-market to make a pie and an Australian buys 1 kg ofapples at the greengrocer to make apple slices, they willboth get the same amount of produce. In this case, thedistinction between mass and weight does not matter.However, to a researcher studying the behaviour of uids,the distinction is essential!PressureThe pressure at any point is the force per unit area actingupon the point. For example, a human of 70 kg standingon the top of an empty aluminium can with a surface areaof 0.002 m2would exert a pressure of70 9.8070.002 ~ 343 000 Nm2or 343 kilopascals (kPa)probably sufcient to crush it.Shear Stress and Shear ForceShear stress, like pressure, is force per unit area. Thedifference is in the direction in which the force is applied.In pressure, the force acts perpendicular to a surface, ,whereas a shear force acts parallel to it, . For example, aglob of liquid soap rubbed between the hands experiencesshearing forces. Shear stress is the shearing force dividedby the area over which it acts. For the soap, the shearingforce acts over the surface area where the soap contactsthe hand. Shear stress, symbolized by t (tau), has the sameunit as pressure, N/m2.Energy and WorkEnergy and work have the same units. Work is a quantitydescribed by the application of a force over some distance,measured in the direction of the force:Work (Nm or J) = Force (N) distance (m) (1.3)For example, if a force of 500 N is required to push awaterlogged log 10 m across a pond, then the amount ofwork done is 5000 N m or 5 kilojoules (kJ).Energy is the capacity for doing work. Thus, thequantity of work that something (or someone) can do isa measure of its energy; e.g. it would take about 700 kJfor a person of average ability to swim 1 km. Energy isusually symbolized by (omega).PowerPower is the amount of work done per unit time:Power (Js or Watts) = Work (J)time (s) (1.4)Power is usually symbolized by . (lower case omega). Fora ow of water, Q, falling over a height, h, the relevantformula for calculating power is. = jgQh (1.5)where . has units of Watts, Q has units of m3/s, h is inmetres, j (rho) is the density of water (kg/m3) and g is theacceleration due to gravity (m/s2). As an approximation,this can be simplied to. = 10Qh (1.6)with . in kilowatts. Thus, if a waterfall of 10 m height isowing at 1.0 m3/s, the power of the falling water is100 kW. If the ow were diverted into a small hydro-electric plant rather than over the waterfall, much of thiswater power could be converted to electrical power.Because of losses associated with the turbine, electricalgenerator and diversion works, efciencies of 70% arecommon. In this example, then, approximately 70 kW ofelectricity could be produced.1.3 Physical Properties of Water1.3.1 Density and Related MeasuresDensityBecause the formlessness of water makes mass anawkward quantity, density, or mass per unit volume, istypically used instead. Density is normally symbolized byj and in the SI system it is expressed in kilograms percubic metre (kg/m3).Introducing the Medium 3Pressure can be assumed to have an insignicant effecton the density of water for most hydrological applications.However, water density does change with temperature,decreasing as the temperature increases above 4 C (i.e.tepid water oats on top of colder water). Water densityreaches a maximum at 4 C under normal atmosphericpressure. As the temperature decreases below 4 C, waterbecomes less dense, and upon freezing, it expands (iceoats). The densities of selected uids at different tem-peratures are listed in Table 1.2.Materials dissolved or suspended in water, such as saltor sediment or air, will also affect its density. Thus, freshwater will oat above salt water in estuarine environmentsor where saline groundwater enters a stream. Density isreduced in the frothy whitewater of rapids, under water-falls or in other areas where large quantities of air areentrained in the water. Swimmers have more troublestaying aoat or propelling themselves in these regions;hence, sh tend to jump towards their upstream destina-tions from less-aerated areas (Hynes, 1970).Specic WeightSpecic weight is a non-SI measure, but is commonly usedin practice in the Imperial system in place of density.Usually symbolized by (gamma), specic weight isequal to the product of density and gravitational acceleration,jg. Thus, in the Imperial system, where the specicweight of water (at 4 C) is 62.4 lb/ft3, one can calculatethe weight of water in a 10 ft3aquarium as 62.4 10 =640 lb. This measure will not be used in this text, and isincluded here only because it appears so often in theliterature.Relative DensityRelative density is usually dened as the ratio of the densityof a given substance to that of water at 4C. It is thus adimensionless quantity (it has no units). For example, therelative density of quartz is about 2.68. Relative density isequivalent to specic gravity, used in the Imperial system,where specic gravity is dened as the ratio of the specicweight of a substance to that of water.Example 1.1Calculate (a) the mass of a 5 L volume of 15 C freshwater and (b) the gravitational force (weight) it experi-ences on Earth:(a) (5 L) .001 m3L 999.1 kgm3 = 5.0 kg(b) 5.0 kg 9.807ms2 = 49.0kg ms2 = 49.0 NTable 1.2. Values of some uid properties at atmospheric pressure. Adapted from Douglas et al. (1983) and Vogel (1981),by permission of Longman Group, UK, and Princeton University Press, respectivelyDynamic KinematicDensity, j viscosity, j viscosity, i(C) (kg/m3) (Ns/m2) (m2/s)Fresh water 0a999.9 1.792 1031.792 1064 1000.0 1.568 1031.568 10610 999.7 1.308 1031.308 10615 999.1 1.140 1031.141 10620 998.2 1.005 1031.007 10625 997.1 0.894 1030.897 10630 995.7 0.801 1030.804 10640 992.2 0.656 1030.661 106Sea waterb0 1028 1.89 1031.84 10620 1024 1.072 1031.047 106Air 0 1.293 17.09 10613.22 10620 1.205 18.08 10615.00 10640 1.128 19.04 10616.88 106SAE 30 oil 20 933 0.26 0.279 103Glycerine 20 1263 1.5 1.190 103Mercury 20 13 546 1.554 1030.115 106aIce at 0C has a density of 917.bSea water of salinity 35 %. The salinity of sea water varies from place to place.4 Stream Hydrology: An Introduction for Ecologists1.3.2 Viscosity and the No-slip ConditionViscosity is a property that is intuitively associated withmotor oil and the relative rates with which honey andwater pour out of a jar. It is related to how rapidly a uidcan be deformed. When a hand-cranked ice cream makeris empty the handle can be turned relatively easily. If it isthen lled with water, the amount of effort increases, andif the water is replaced with molasses, the handle becomesextremely difcult to turn. Viscosity, or more precisely,dynamic or absolute viscosity, is a measure of this increas-ing resistance to turning. It has units of Newton secondsper square metre (Ns/m2) and is symbolized by j (mu).Of interest to aquatic organisms and aquatic researchers isthe fact that there is almost no liquid with viscosity lowerthan that of water (Purcell, 1977).The dynamic viscosity of water is strongly temperaturedependent. Colder water is more syrupy than warmerwater. For this reason, it takes less effort for a waterboatman to row across a tepid backyard pond in summerthan the equivalent distance in a frigid high-country lake.It also takes more work for wind to produce waves on awater surface when the water is colder. Dynamic viscosityof fresh water can be calculated directly from tempera-ture using the Poiseulle relationship, given as follows(Stelczer, 1987):j = 0.0018(1 0.0337T 0.00022T2) (1.7)Eq. (1.7) will give slightly different values than thoselisted in Table 1.2 for fresh water. It should be noted thatsalt water has a higher dynamic viscosity than fresh waterat the same temperature. Vogel (1981) describes instru-ments for measuring the viscosity of uids for whichpublished values are not available.The inuence of viscosity is perhaps most signicant inthe region where uids come into contact with solids. It ishere that uids experience the equivalent of friction,which develops entirely within the uid. When a solidslides across another solid, like shoes across a carpet,friction occurs at the interface between the two solids.When a uid encounters a solid, however, the uid sticksto it. There is no movement at the interface. According tothis no-slip condition, at the point where a viscous uidcontacts a solid surface like a cobble on a streambed or ascale on a sh, its velocity is the same as that of the solid.Thus, when water ows by a stationary solid object, thevelocity of the water is zero where it contacts the solidsurface, increasing to some maximum value in the freestreamthe region free of the inuence of the solidboundary.Kinematic viscosity, symbolized by i (nu), is the ratioof dynamic viscosity to density:Kinematic viscosity (i) = Dynamic viscosity (j)Density (j) (1.8)where i has units of m2s. This ratio shows up frequentlyin important measures such as the Reynolds number, andis another way of describing how easily uids ow. Thequantity was introduced by engineers to simplify theexpression of viscosity (kinematic viscosity has dimen-sions only of length and time).From Table 1.2 it can be seen that the kinematicviscosities of air and water are much more similar thantheir relative dynamic viscosities. The similarities in thebehaviour of air and water make it convenient to model aircurrents, chimney plumes or aircraft in water tanks (afterapplying appropriate scaling factors).1.3.3 Surface TensionA whirligig beetle darting across the surface of a pool,beads of dew on a waxy leaf, the curve of water spillingover a weir and the creep of water upwards from thegroundwater table into ne-grained soilsare all illustra-tions of the phenomenon, surface tension. Surface tensioncan be regarded as the stretching force per unit length (orenergy per unit area) required to form a lm or mem-brane at the airwater interface (Streeter and Wylie,1979). It is symbolized by o (sigma), and has units ofNewton per metre (N/m).Surface tension of water in contact with air results fromthe attraction of water molecules to each other. Within abody of water, a water molecule is attracted by themolecules surrounding it on all sides, but molecules atthe surface are only attracted by those beneath them.Therefore, there is a net pull downwards which putstension on the water surface. The surface region undertension is commonly known as the surface lm. Becausethis lm is under tension, any change in shape whichwould add more surface area (and further increase thetension) is resisted. Water drops and submerged airbubbles, as examples of airwater interfaces, are almostperfectly spherical because a sphere has less surface areaper unit of volume than other shapes.The surface tension of water is temperature-dependent.It decreases as temperature rises by the following relation-ship (Stelczer, 1987):o = 0.0755 0.000 156 9T (1.9)Introducing the Medium 5Surface tension also affects whether a droplet will beadup or spread out on a solid surface. The angle of contactbetween a liquid and a solid is related not only to thecohesion of the water molecules (attraction to each other),but also to the adhesion of the liquid to the solid. If thiscontact angle (0 in Figure 1.1(a)) is less than 90, theliquid is said to wet the solid. If the angle is greater than90, the liquid is non-wetting.Water is wetting to a clean glass surface or a bar of soapbut does not wet wax (White, 1986). Non-wettable objectswith a higher density than water can be supported by thesurface lm up to a certain point. For example in water at18 C, a dry sewing needle of 0.2 g will oat, whereas at50 C, it will sink. Near sandy streambanks, patches ofne dry sand may likewise be supported by the watersurface. Insects that dart around on the water surface tendto have a waxy coating which functions as a waterrepellant (Vogel, 1988).Adding a wetting agent such as detergent to the waterwill reduce the surface tension, making it more difcultfor mosquitoes to attach to the surface lm from theunderside or for water-striding insects to walk across it. Ifa baby duck is placed in a tub of soapy water, the water-repelling oil in its feathers dissolves, releasing air trappedwithin the feathers, and it sinks (Bolemon, 1989). Cor-morants do not have water-repellent feathers, and mustspread their wings out to dry after diving for sh.Wetting agents are added to liquid pesticides to makethem spread out and cover more surface area on plantleaves. Similarly, laundry detergents reduce surface ten-sion, allowing water to penetrate more readily through dryclothes (Vogel, 1988).Another important implication of surface tension is thatpressure within a droplet of water in airor within an airbubble under wateris higher than the pressure outside.The increase in pressure is given by (White, 1986)p = 2or (1.10)where p is the increase in pressure (in N/m2) due tosurface tension and r is the radius (in metres) of theFigure 1.1. Effects of surface tension (a) on the angle of contact, 0, in wetting and non-wetting liquids and (b) on capillarity incircular glass tubes of radius r, where h is capillary rise or depression6 Stream Hydrology: An Introduction for Ecologistsdroplet or bubble. It can be seen that the pressure becomeslarger as the radius gets smaller. Because of the increasedpressure, the air held in small bubbles will tend to go intosolution and the bubble will shrink. Thus, very small airbubbles will quickly collapse and disappear. Vogel (1988)offers a fascinating discussion on how bubbles form atscratched surfaces in beer glasses and other biologicallyrelated implications of surface tension.Capillarity is another phenomenon caused by surfacetension. Capillarity, which causes water to rise in plantstems, soil pores and thin glass tubes, results from bothadhesion and cohesion. Its height is positive (capillaryrise) if liquids are wetting and negative (capillary depres-sion) if liquids are non-wetting, as shown in Figure 1.1(b).Also, the meniscus (curve of the liquids surface) isconcave for wetting liquids and convex for non-wetting.The formula for capillary rise (or depression), h (m), is(White, 1986)h = 2ocos 0jgr (1.11)where r is the radius (m) of the tube or the mean radius ofsoil pores, j is the density of the water (kg/m3) and theother symbols have been explained earlier in this section.From Eq. (1.11) it can be seen that capillarity decreasesas the tube or pore radius gets bigger. For water in glasstubes with diameters over about 12 mm, capillary actionbecomes negligible (Daugherty et al., 1985). It can also beseen that h is positive for 0 < 90 (wetting liquids) andnegative for 0 90 (non-wetting). For open-water sur-faces and soil pores the simplication 0 = 0 is usuallymade so that the (cos 0) term drops off (Stelczer, 1987). Insoils, organic matter and certain mineral types canincrease the contact angle above 90, in which case thesoil will not wet. For example, soils can become hydro-phobic after intense res, preventing water from inltrat-ing (Branson et al., 1981).1.3.4 Thermal PropertiesTemperature has an effect on other properties of water,such as density, viscosity and dissolved oxygen concen-tration. Temperatures vary seasonally in streams and withthe water source (e.g. snowmelt or industrial outfall).Because of turbulence, the thermal stratication charac-teristic of lakes is uncommon in streams and they respondmore quickly to changes in air temperature. Biologically,temperature has an important inuence on decompositionand metabolic rates, and thermal cues may exist forreproduction or migration; therefore, aquatic organismswill survive and thrive within specic temperature ranges.Streams, as a rule, exist between the temperatureextremes of ice oes and boiling hot springs. Pure waterfreezes at 0 C and boils at 100 C. The presence ofdissolved solids raises the boiling point and depressesthe freezing point as compared with pure water. Sinceaquatic organisms normally concentrate salts in differentproportions to those in the surrounding solution, theirboiling and freezing temperatures will be differentfrom those of the surrounding medium, and some primi-tive organisms such as blue-green algae and bacteria cantolerate great extremes of temperature.In studies of aquatic systems, temperature data aresometimes converted to degree-days to correlate tempera-ture with snowmelt, plant germination times or develop-mental times for aquatic insects, wheredegree-days = nTavg (1.12)Here, n is the number of days from a given starting dateand Tavg is the mean daily temperature above some base,usually 0C (Linsley et al., 1975b). Four days withindividual mean temperatures of 20, 25, 25 and 30Cwould therefore represent 100 degree-days above 0C.The amount of heat a body of water absorbs depends onthe amount of heat transferred to it from the air andstreambanks, as well as the thermal capacity of the water.The thermal capacity of water is very high in comparisonwith other substances, meaning that it can absorb a largeamount of heat before its temperature increases substan-tially. Thermal capacity, Tc, has units of J/C, and isdened as (Stelczer, 1987)Tc = cM (1.13)where M is the mass of water (kg) and c is the specicheat of the water (J/kg C). Specic heat is the amountof heat required to raise the temperature of a unitmass of water by 1 C. As shown in Table 1.3, it isTable 1.3. Values of specic heat for water at varioustemperatures. From Stelczer (1987), Reproduced bypermission of Water Resources Publications, LLCWater temperature (C) Specic heat (J/kgC)Ice 2.0390 4.20610 4.19120 4.18130 4.17640 4.17750 4.183Introducing the Medium 7temperature-dependent, reaching a minimum at 30 C.Thus, a kilogram of water at 10 C would require 4.19 Jof heat energy to raise its temperature to 11 C.Energy is released when water freezes, a fact known bycitrus fruit growers who spray their trees with water toprotect them from frost damage. The latent heat of fusion,the energy needed to melt ice or the energy which mustbe taken away for it to freeze, is 335 kJ/kg for water at0 C.At the other extreme, additional energy is requiredwhen water reaches the boiling point to get it to vaporize.Vaporization reduces the temperature of the remainingwater. The latent heat of vaporization for water at 100 Cis 2256 kJ/kg. These latent heat values are relatively highin the natural world and are caused by hydrogen bonding.Hydrogen bonding is also responsible for the unusualbehaviour of water density near the freezing point.1.3.5 Entrained Air and Dissolved OxygenDissolved oxygen (DO) is actually a chemical property ofwater, but is included because it is affected by physicalproperties such as temperature and turbulence, andbecause of its biological relevance. Oxygen enters waterby diffusion at the interface between air and water at thesurface of a stream or at the surface of air bubbles. It canalso be produced from the photosynthesis of aquaticplants.Entrainment of air under waterfalls and in the frothywhitewater of rapids increases the amount of interfacearea where diffusion can occur. Most of this entrained airsoon escapes, however, and it is the escape of these airbubbles which produces the roar of rapids and themurmur of meandering brooks (Newbury, 1984). Theamount of air remaining in the water is determined bythe gas-absorbing capacity of water, which is dependentupon temperature and ambient pressure.Under normal atmospheric pressure and a temperatureof 20 C, water will contain about 2% (by volume)dissolved air (Stelczer, 1987). As temperatures rise, thegas-absorbing capacity of water decreases rapidly, reach-ing zero at 100 C. Although the concentration of oxygen(O2) in the atmosphere is about 21%, oxygen is moreTable 1.4. Dissolved oxygen saturation concentrations atatmospheric pressure 760 mmHg and zero salinity.Generated from USGS DOTABLES program (USGS, 2001),Reproduced by permission of U.S. Geological SurveyWater temperature (C) Oxygen saturation (mg/L)0 14.65 12.710 11.315 10.120 9.125 8.230 7.540 6.4Distance downstreamDissolved oxygen (DO)Critical point of minimum DOOxygen deficitSaturationlevelRe-aeration fromatmosphereContinuous sourceof organic matterFigure 1.2. Dissolved oxygen sag curve8 Stream Hydrology: An Introduction for Ecologistssoluble in water than nitrogen, and dissolved air containsfrom 33% to 35% O2, depending on the temperatureafact which has no doubt played an evolutionary role in thedimensions of gills and other respiratory mechanisms.The maximum amount of dissolved oxygen that watercan hold at a given temperature, atmospheric pressureand salinity is termed oxygen saturation. Table 1.4 givesoxygen saturation values for a range of water tempera-tures.The amount of DO actually present in the water can beexpressed as a percentage of the saturation value (% sat)%sat = Actual DO concentrationSaturation concentration 100 (1.14)Concentrations are usually given in milligrams per litre(mg/L). For example, if a 20C water sample has a DOcontent of 8.2 mg/L, then %sat =(8.2/9.05) 100 =90.6%.Organic matter in streams is assimilated by bacteria thatuse dissolved oxygen for the aerobic processing of organicmaterials. An increase in the amount of organic matter(e.g. sewage, detritus stirred up by dredging or anoverload of autumn leaves in temperate climate zones)stimulates bacterial growth. If the organic load is extre-mely excessive, nearly all the dissolved oxygen can beused up by the bacteria, leading to anaerobic conditions.In these streams, conditions can become unfavourable toforms of aquatic life sensitive to oxygen levels (Best andRoss, 1977).The process of de-oxygenation and re-aeration ofstreams produces a pattern in the DO concentrationknown as the dissolved oxygen sag, rst described byStreeter and Phelps in 1925 (Clark et al., 1977). A sagcurve is illustrated in Figure 1.2, representing the dis-solved oxygen decit (amount below saturation level) as itvaries with distance downstream. A light organic load andadequate aeration will only cause a slight dip in the curvewith a quick recovery, whereas a heavy load and low re-aeration rate may cause DO to decrease to 0%, fromwhich it recovers only slowly. Equations for estimating thesag curve are given by Clark et al. (1977, pp. 296298),and require eld studies to determine the degree oforganic pollution and the re-aeration characteristics ofthe stream.Introducing the Medium 92How to Study a Stream2.1 Focusing on Physical HabitatBefore beginning, the denitions of the terms river, streamand catchment should be claried. In general, rivers arelarger paths of moving water (i.e. too large to wade orjump across) and streams or creeks are smaller. Thisrelative denition will be retained, but the word streamwill be used as a generic term for owing waters through-out the text. A catchment is the area above a specic pointon a stream from which water drains towards the stream.Catchments and their characteristics will be describedfurther in Chapter 3.At the interface between aquatic ecology and hydrol-ogy, studies of streams fall roughly into the followingcategories:1. Description or classication of aquatic habitats basedon their biota and environmental characteristics.Descriptions of the owing environment are alsoneeded for simulating the same conditions in labora-tory umes.2. Monitoring programs to determine variability in thenatural environment over time or to detect some trenddue to environmental deterioration or recovery (Green,1979).3. Comparison of conditions at one place/time withconditions at another place/time; e.g. comparingeffects of management or of some experimental treat-ment, either between sites or at the same site atdifferent times (Platts et al., 1987).4. Development of relationships between variables, e.g.local water velocity and blacky larvae populations, orcatchment area and stream width, in order to estimateor predict one from the other(s).A variety of factors control the abundance, distributionand productivity of stream-dwelling organisms such ascompetition for space, predation, chemical water quality,temperature, nutrient supplies, the presence of waterfallsor dams and ow variability. An individual species willhave a range of tolerance to any given factor, with somefactors more critical than others. Thus, studies of streamsmay involve the measurement and analysis of biological,chemical and physical parameters. The emphasis through-out this text, however, will be on physical habitat: thosefactors which form the structure within which an organ-ism makes its home. Physical factors are generally morepredictable, less variable and more easily measured thanbiological or chemical ones, and are thus preferable forgeneral, consistent descriptions of streams.Following is a discussion of the physical factors whichare of the most ecological signicance: streamow, cur-rent (velocity), channel shape, substrate and temperature.Dissolved oxygen and salinity, although chemical factors,have been included since they are inuenced by physicalfactors, they have high ecological relevance and they canbe measured relatively easily. Vegetation has also beenincluded as a related factor because of its inuence on thephysical nature of streams. These factors should beconsidered when planning a stream study (Section 2.2)and developing a sampling design (Sections 2.32.5).More information on the effects of physical factors onthe distribution of biota can be obtained from texts onaquatic biology or stream ecology such as Allan (2001),Barnes and Mann (1980), Bayly and Williams (1973),Brown (1971), DeDeckker and Williams (1986), Fontaineand Bartell (1983), Goldman and Horne (1983), Hynes(1970), Maitland (1978), Moss (1988), Resh and Rosen-berg (1984), Townsend (1980), Uhlmann (1979) andWelch (1935).Stream Hydrology: An Introduction for Ecologists, Second Edition.Nancy D. Gordon, Thomas A. McMahon, Brian L. Finlayson, Christopher J. Gippel, Rory J. Nathan#2004 John Wiley & Sons, Ltd ISBNs: 0-470-84357-8 (HB); 0-470-84358-6 (PB)StreamowAs a general trend, streamow increases and channels getlarger in the downstream direction. Patterns of physicalhabitats are created along a stream and within the pools,rifes and boulder clusters within particular streamreaches. These habitats and their inhabitants vary withpatterns of streamow. Ephemeral streams (Section 4.1.3),for example, usually (but not always) support differentspecies than perennial streams. Snowmelt-fed and spring-fed streams generally have more predictable and lessvariable ow patterns than rainfall-fed ones, and theirora and fauna will be different. In highly variablestreams, organisms may require more exibility in theirfeeding, growth and/or reproductive behaviours. Fishcommunity patterns also tend to be inuenced more bythe streamow in variable streams, and more by biologicalfactors such as competition, predation or food resources instable streams (Pusey and Arthington, 1990).Floods and droughts can have signicant impacts onriverine species. Periodic scouring of banksides and inun-dation of oodplains regulate plant growth and nutrientinput to the stream. Patterns of ooding affect the dis-tribution of plant species within the stream and along agradient from the rivers edge to upland areas. Prolongedooding of wetlands is needed for waterbirds to feed, restand reproduce. The survival of juvenile sh may alsodepend on the inundation of oodplains, billabongs andbackwaters. Moreover, oods serve as a signal for somesh species that it is time to spawn. Floods turn overrocks, altering the conguration of the streambed andresetting the ecosystem by allowing a succession oforganisms to re-colonize the substrate.During low ows, temperature and salinity levels mayrise, and plant growth within the channel can increase.Some species may rely on low ow periods for a part oftheir life history; for others, it is a time of stress. Thestream may dry to a series of scattered pools connectedonly by sub-surface ows, limiting movement andincreasing predation and competition for nutrients andspace within the remaining waters. Intermittent streamsexperience a greater range of physical and chemicalvariation (e.g. in temperature and dissolved oxygenlevels), and thus support unique biologic communities.These streams generally have a lower species richness ascompared to perennial ones (Lake et al., 1985). To copewith temporary waters, some organisms have developedspecial adaptations, such as dormant phases, which allowthem to survive. Some larvae of aquatic insects, forexample, burrow deep into the streambed to nd sufcientmoisture. Other species have drought-resistant eggs orspores and quick regenerative powers for the time whenfavourable conditions return. If only part of a stream runsdry, the affected reaches can be re-populated from remain-ing pools or upstream tributaries. Williams (1987) pro-vides additional information on the ecology of intermittentstreams.Streamow is a particularly important factor in thestudy of regulated waters, where modications to naturalow patterns can have marked effects on the streams oraand fauna.CurrentAs stated by Hynes (1970, p. 121), current is the mostsignicant characteristic of running water, and it is in theiradaptations to constantly owing water that many streamanimals differ from their still-water relatives. Somespecies have an innate demand for high water velocities,relying on them to provide a continual replenishment ofnutrients and oxygen, to carry away waste products and toassist in the dispersal of the species. At a given tempera-ture, the metabolic rate of plants and animals is generallyhigher in running water than in still water (Hynes, 1970).However, it takes a great deal of energy to maintainposition in swift waters, and most inhabitants of thesezones have special mechanisms for avoiding or with-standing the current.On average, water velocity tends to increase in thedownstream direction, even though mountain torrents givethe impression of high speeds in comparison to the moresluggish-looking lowland streams. Within a particularregion, however, local variations create a mosaic ofpatterns which support species with different preferences.The velocities actually encountered, then, are of morerelevance than average velocities (Armour et al., 1983).As ow levels increase, velocity patterns will shift, for-cing organisms to nd refuge in calmer backwaters,behind rocks or snags, within vegetation stands or beneaththe streambed.At a ner scale, the leaves and stems of plants or thearrangements of rocks can vary the local ow environ-ment, creating micro-habitats for other organisms. Mov-ing even closer to the surfaces of these features, very smallanimals such as protozoans can live in a thin uid layer ofnear-zero velocity. Complex communities of bacteria,fungi, protozoans and other microscopic organismsform biolms on surfaces within the stream, whichconstantly grow and slough off under the inuence ofthe current.A factor related to velocity patterns is turbulence, whichis important in the aeration of waters and the ability of astream to carry sediments. Turbulence has a buffetingeffect on organisms exposed to the current. Near the12 Stream Hydrology: An Introduction for Ecologistsstreambed, organisms may feed at the edges of smallturbulent vortices that stir up the substrate and circulatefoodstuffs.Current affects the distribution of sediments on thestreambed through its inuence on lift and drag forces.Organisms subject to these same forces often show mor-phological adaptations such as streamlined or attenedbodies or the presence of hooks or suckers for clinging tothe substrate. Blacky larvae (Diptera: Simuliidae), char-acteristic of very fast waters, attach to the substrate withhooks and have a silk lifeline with which to reelthemselves in when they are dislodged. Stream-dwellingmollusc species have heavier, thicker shells than still-water forms, perhaps for ballast as well as protection frommoving stones (Hynes, 1970). Species of sh which mustnegotiate strong currents tend to be streamlined, whereasthose which spend almost all of their time near thestreambed are more attened from top to bottom (Town-send, 1980).Species unable to tolerate high currents may use beha-vioural mechanisms to escape by burrowing into thestreambed, hiding under rocks or building shelters. Fishand eels utilize the dead water regions behind rocks forshelter, moving in short bursts from one to the next.The distribution of current within a stream can beconsiderably affected by channel modications such asde-snagging or straightening. The comparison of velocitydistributions in modied and unmodied streams is valu-able in stream rehabilitation work.Water Depth and WidthA streams depth and width is related to the amount ofwater owing through it. However, variations in channelform such as pools and rifes, wide meander loops andsand bars will create variation in water width and deptheven where the streamow is the same.Water depth has an inuence on water temperature,since shallow water tends to heat up and cool down morerapidly. It affects light penetration (more so in turbidwaters), inuencing the depth at which aquatic plantshave enough energy for photosynthesis. Hydrostatic pres-sures also increase with depth, affecting the internal gasspaces in both plants and animals.Depth affects the distribution of benthic invertebrates,with most preferring relatively shallow depths (Wesche,1985). Both depth and width affect the physical spacingbetween predator and prey species. In general, larger shprefer to live in pools and smaller sh in shallower water.Depth may become a limiting factor for sh migrationwhen the water is too shallow for passage. Changes inwater level can also affect the survival of species (e.g. bystranding sh or eggs, or inundating seedlings at thewrong time).According to Pennak (1971), the width of a streamdetermines much of its biology. Migrating birds mayrequire open riverine corridors for navigation and a certainwidth of water not obstructed by trees for landing andtake-off. For resting and nesting, some waterbirds need awater barrier of a certain width to protect them frompredators. Mammals such as beavers also have specicrequirements for width, depth and slope (Statzner et al.,1988). For terrestrial animals, width and depth will affecttheir ability to migrate from one side of a stream to theother.Geomorphologically, width increases in the down-stream direction and the shading of streams by over-hanging streamside vegetation decreases. Thus, asstreams increase in width downstream, organic inputfrom riparian vegetation becomes less signicant andinstream photosynthesis increases.SubstrateIn a stream, substrate usually refers to the particles onthe streambed, both organic and inorganic. Inorganicparticle sizes generally decrease in the downstream direc-tion. On a more local scale, larger particles (gravel,cobble) are associated with faster currents and smallerparticles (sand, silt, clay) with slower ones. Generally,streambeds composed of smaller particles are less stable,but this will also depend on the mix of particle sizes andshapes. Studies of substrate composition should considerthe average and range of particle sizes, the degree ofpacking or imbeddedness and the irregularity or roundnessof individual particles.Substrate is a major factor controlling the occurrence ofbenthic (bottom-dwelling) animals. A fairly sharp distinc-tion exists between the types of fauna found on hardstreambeds such as bedrock or large stones and soft onescomposed of shifting sands. Slow-growing algae, forexample, require stable substrates such as large boulders(Hynes, 1970). Additionally, a whole complex of micro-fauna can occur quite deep within streambeds (in thehyporheic zone). These may carry out most or all of theirlife histories underground.In general, lowland streams with unstable beds tend tohave a lower diversity of aquatic animals. Aquatic plants,however, may prefer ner substrates, the plants thenbecoming substrates for other organisms. Silt substratesmay support high populations of burrowing animals,particularly if the silt is rich in organic matter. Freshwatermussels, for example, mostly occur in silty or sandybeds. Clay substrates typically become compacted intoHow to Study a Stream 13hardpan (Pennak, 1971), supporting little except encrust-ing algae and snails.The greatest numbers of species are usually associatedwith complex substrates of stone, gravels and sand. Themix of coarser particles in rifes provides the richestaquatic insect habitat, and is considered the sh foodproduction zone in upland streams. Larger substratematerials provide rmer anchoring surfaces for aquaticinsects and more shelter is available in the form ofcrevices and irregular-shaped stones. Crustaceans suchas freshwater craysh also require rock crevices for shelter.Fish require substrates that provide shelter from thecurrent, places for hiding from predators and sites fordepositing and incubating eggs. Salmonids, for example,dig nest-like redds in gravel substrates by lifting particleswith a vacuum-generating sweep of their tails. Successfulincubation of the deposited eggs depends on circulation ofwater through the gravels to supply oxygen and carryaway waste products.Streambed particles are subject to dislodgement duringoods, from dredging or other human disturbances and toa much lesser extent when the activities of bottom-feedingsh or burrowing animals stir up sediments. Suspendedsediments reduce light penetration and thus plant growth;they can also damage the gills of insects and sh. Largergrains in suspension can have a sandblasting effect onorganisms, and rolling stones can crush or scour awaybenthic plants and animals.The composition of stream substrates can be altered bysediment inuxes from upland erosion and by channelmodication. Excessive siltation of gravel and cobblebeds can lead to suffocation of sh eggs and aquaticinsect larvae and can affect aquatic plant densities. This,in turn, can result in changes in mollusc, crustacean andsh populations. Generally, these changes tend to cause ashift towards downstream conditions (i.e. unstable beds ofne materials), effectively extending lowland river eco-systems further upstream.TemperatureIn general, water temperature increases in the downstreamdirection, to a point where the water reaches an equili-brium with air temperatures. Water temperature changesboth seasonally and daily, but to a lesser degree than airtemperature. Seasonal uctuations tend to be more extreme inlowland streams whereas daily uctuations may be moreextreme in the smaller, upland ones, especially where theyare unprotected by vegetation or other cover. In temperateor cold climates, upstream reaches may actually remainwarmer in the winter than those downstream, particularlywhen these upper reaches are spring-fed.Local variations in shade, wind, stream depth, watersources (e.g. hot springs) and the presence of impound-ments will alter the general trends caused by geographicalposition. Many organisms take advantage of these localvariations. For example, Wesche (1985) cites studieswhich have shown that some trout species select spawningsites in areas with groundwater seepage, where the war-mer waters protect eggs from freezing and reduce hatch-ing times.When water cools (above 4 C), it becomes denser andsinks. In most stream reaches, turbulence keeps the waterwell mixed, but temperature stratication can occur wherewaters are more stagnant, such as in deep pools. One ofthe unique properties of water is that it is less dense as asolid. In winter, ice and snow can form an insulatingblanket over streams, under which aquatic life can con-tinue. Ice usually starts forming when the entire watermass nears 0 C, beginning with low-velocity areas nearthe edges of streams, along the streambed and on theunderwater surfaces of plants.The temperature of a stream is critical to aquaticorganisms through its effects on their metabolic ratesand thus growth and development times. With the excep-tion of a few aquatic birds and mammals, most aquaticanimals are cold blooded, i.e. their internal temperaturesclosely follow that of the surrounding water. As a generalrule, a rise of 1 C increases the rate of metabolism incold-blooded aquatic animals by about 10%. Thus, theseaquatic organisms will respire more and eat more inwarmer waters than in colder ones. Each organism willhave maximum and minimum temperatures betweenwhich they can survive, and these limits may changewith each life stage. For sh, unusually high temperaturescan lead to disease outbreaks, cause the inhibition ofgrowth and cause sh to stop migrating (Platts, 1983).Water temperature is thus an important factor in reg-ulating the occurrence and distribution of riparian vegeta-tion, sh, invertebrates and other organisms. Becausetemperature also affects other properties of water suchas viscosity and concentrations of nutrients and dissolvedoxygen, it can be difcult to separate the direct effects oftemperature from the indirect effects of these other prop-erties. Stream classication systems (Chapter 9) ofteninclude water temperature as a factor.Dissolved OxygenDissolved oxygen (DO) is essential for respiration inaquatic animals as well as being an important componentin the cycling of organic matter within a stream. Since gassolubility generally decreases as the water temperaturerises, this can lead to lower DO levels during the summer.14 Stream Hydrology: An Introduction for EcologistsAs mentioned in Section 1.3.5, the oxygen concentra-tion of air dissolved in water is higher than it is in theatmosphere. Some organisms use this property indirectly,such as beetles that carry bubbles of air underwater tofunction as gillsoxygen diffuses into the bubble fromthe surrounding water as it is used (Hynes, 1970).In the turbulent, well-mixed waters of upland streams,dissolved oxygen concentrations are usually near satura-tion levels. As these turbulent reaches gradually give wayto more poorly mixed waters downstream, biologicalsources of oxygen become more important. Photosynth-esis can actually super-saturate the water with oxygenduring the day. Then, night-time respiration and decom-position demands for oxygen can lead to diurnal changesin DO level. Diurnal variations in DO have been used as abasis for computing primary production in streams (Baylyand Williams, 1973).The distribution of DO inuences the patterns ofspecies found along streams. Carp, tench and bream, forexample can survive in low-oxygen waters, whereas troutrequire higher levels. The amount of oxygen will alsoaffect the activity of organisms. As mentioned by Hynes(1970), the swimming speed of young salmon varies withDO concentration.Oxygen is suppl