TT 453/10 E nd Guid A w E vi E Editors: CS James & JM King CS James Editors: A R Ecohydraulics for South African for Rivers Ecohydraulics TT 453/10 Ecohydraulics for South African Rivers – Ai REv Ew And GuidE Ecohydraulics for South African Rivers A Review and Guide Editors : C S James and J M King Report to the Water Research Commission by Ninham Shand Consulting Services in association with The Freshwater Consulting Group, The Centre for Water and the Environment and Streamflow Solutions WRC Report No. TT 453/10 April 2010 Obtainable from: Water Research Commission Private Bag X03 Gezina 0031 The publication of this report emanates from a project entitled: South African Handbook on Environmental River Hydraulics (WRC Project No. K5/1767) DISCLAIMER This report has been reviewed by the Water Research Commission (WRC)and approved for publication. Approval does not signify that the contents necessarily reflect the views and policies of the WRC, nor does mention of trade names or commercial products constitute endorsement or recommendation for use. ISBN 978-1-77005-960-3 Printed in the Republic of South Africa i PREFACE Ecohydraulics is defined as the study of the linkages between physical processes and ecological responses in rivers, estuaries and wetlands (Centre for Ecohydraulics Research, Univ. Idaho, 2006). Since the early 1990s, the science of ecohydraulics has developed at a rapid pace. This was mainly in response to the need to inform Ecological Water Requirement and river rehabilitation studies aimed at predicting and mitigating the impacts of changes in flow and sediment regimes on river ecosystems. Essentially, these studies assess the magnitude and timing of flows necessary to maintain a river ecosystem in a pre- determined, environmentally acceptable condition, with ecohydraulics providing a tool to characterise the relationship between discharge and the availability of physical (hydraulic) habitat within the river ecosystem. Based on this relationship and an understanding of the hydraulic conditions that are optimal for different species or communities, ecohydraulic modeling is employed to predict how hydraulic conditions in a river might change under different development scenarios and thus, how the aquatic habitat of specific species or communities could be affected. Over the past almost twenty years in South Africa, a great deal of knowledge on ecohydraulics, related to both research and application, has been gained through several projects involving the Water Research Commission, the Department of Water Affairs and Forestry and other institutions in South Africa. The realisation that this information and knowledge are fragmented and often inconsistent across various knowledge centres and disciplines, e.g. aquatic ecology, riverine vegetation, sedimentation, fluvial morphology and fundamental hydraulics, prompted this project, the objective of which was to provide a synthesis of existing knowledge on ecohydraulics in South Africa in a logical and accessible format. Not only does this document present theories and techniques related to ecohydraulics, it also provides the ecological context and perspective for the application of ecohydraulics and as such builds capacity amongst both engineers and ecologists and contributes towards the effective management of our aquatic environment. Furthermore, as this document provides an overview of the current state of ecohydraulics research in South Africa, it serves as a useful point of reference for identifying and prioritising future research needs for ecohydraulics in South Africa. ii ACKNOWLEDGEMENTS The Study Team would like to thank the Water Research Commission for funding this project. The members of the Reference Group are as follows: Dr R Dube Water Research Commission, Chairman Mr D Grobler Blue Science Consulting Dr A Jordanova Golder Associates Dr C Brown Southern Waters Dr C J Kleynhans DWAF Ms R Stassen DWAF Mr P van Niekerk DWAF The contribution of the following participants is also gratefully acknowledged: Mr P Hirschowitz SSI Ms W Kloppers DWAF Mr M Rountree University of the Witwatersrand iii LIST OF CONTRIBUTORS B ABBAN Ninham Shand (Pty) Ltd, P O Box 1347, Cape Town 8000 A L BIRKHEAD Streamflow Solutions, P O Box 889, Gonubie 5256 J D S CULLIS Ninham Shand (Pty) Ltd, P O Box 1347, Cape Town 8000 C S JAMES Centre for Water in the Environment, School of Civil & Environmental Engineering, University of the Witwatersrand, Private Bag 3, Wits 2050 V JONKER Ninham Shand (Pty) Ltd, P O Box 1347, Cape Town 8000 J M KING Freshwater Research Unit, Zoology Department, University of Cape Town, Rondebosch 7701 M T KLEYNHANS Ninham Shand (Pty) Ltd, P O Box 1347, Cape Town 8000 B R PAXTON Freshwater Research Unit, Zoology Department, University of Cape Town, Rondebosch 7701 G R RACTLIFFE Freshwater Research Unit, Zoology Department, University of Cape Town, Rondebosch 7701 M J SHAND Ninham Shand (Pty) Ltd, P O Box 1347, Cape Town 8000 iv v TABLE OF CONTENTS PREFACE……………………………………………………………………………………………….... i ACKNOWLEDGEMENTS……………………………………………………………………………... ii LIST OF CONTRIBUTORS………………………………………………………………………….…iii TABLE OF CONTENTS……………………………………………………………………………….. .v LIST OF TABLES…………………………………………………………………………………….. .viii LIST OF FIGURES …………………………………………………………………………………….. ix LIST OF ABBREVIATIONS AND ACRONYMS……………………………………………………xiii GLOSSARY………………………………………………………………………………………………xv PART I : INTRODUCTION 1. INTRODUCTION..................................................................................................................1 1.1 Background…………………………………………………………………………………………. 1 1.2 Objectives…………………………………………………………………………………………… 1 1.3 Report Layout………………………………………………………………………………………. 2 PART II : ECOLOGICAL CONTEXT 2. PATTERNS AND PROCESSES IN THE RIVER LANDSCAPE .......................................... 4 2.1 Introduction…………………………………………………………………………………………. 4 2.2 Broad-scale spatial pattern………………………………………………………………………….. 4 2.2.1 South African bioregions and ecoregions .............................................................................4 2.2.2 Catchment signatures ............................................................................................................7 2.3 The four-dimensional river………………………………………………………………………….. 7 2.3.1 The longitudinal dimension ..................................................................................................8 2.3.2 The vertical dimension – the hidden domain ...................................................................... 15 2.3.3 The lateral dimension – beyond the wetted edge ................................................................ 17 2.3.4 The temporal dimension...................................................................................................... 20 2.4 Conclusion………………………………………………………………………………………… 28 2.5 References…………………………………………………………………………………………. 28 3. THE RIVER AS A LIVING SYSTEM ..................................................................................32 3.1 Introduction………………………………………………………………………………………... 32 3.2 Life in running water……………………………………………………………………………… 33 3.2.1 Morphological adaptations .................................................................................................. 34 3.2.2 Physiological adaptations .................................................................................................... 35 3.2.3 Behavioural adaptations ......................................................................................................36 3.2.4 Life cycle strategies ............................................................................................................ 36 3.3 Biological links to the flow regime………………………………………………………………39 3.3.1 Flow categories and riverine plants .................................................................................... 39 3.3.2 Invertebrates and floods ...................................................................................................... 41 3.4 Stream communities – revisiting disturbance……………………………………………………... 42 3.5 Conclusion………………………………………………………………………………………… 45 vi 3.6 References………………………………………………………………………………………… 45 4. DESCRIBING HYDRAULIC HABITAT ............................................................................... 48 4.1 Introduction……………………………………………………………………………………….. 48 4.2 Flows and channel morphology…………………………………………………………………… 48 4.2.1 River channels ..................................................................................................................... 48 4.2.2 River floodplains ................................................................................................................. 50 4.3 Flows and aquatic, riparian and floodplain vegetation……………………………………………. 51 4.4 Fish and invertebrates……………………………………………………………………………54 4.4.1 Habitat Suitability Criteria .................................................................................................. 54 4.4.2 Flow classes ........................................................................................................................ 60 4.4.3 Hydraulic biotopes .............................................................................................................. 63 4.5 Boundary-layer, benthic and hyporheic flows…………………………………………………….. 68 4.6 Conclusion………………………………………………………………………………………… 68 4.7 References…………………………………………………………………………………………. 69 5. ECOLOGICAL ISSUES IN RIVER FLOW MANAGEMENT AND THE CHALLENGES FOR ECOHYDRAULICS ..........................................................................75