Geomorphological Change and River Rehabilitation Alterra is the main Dutch centre of expertise on rural areas and water management. It was founded 1 January 2000. Alterra combines a huge range of expertise on rural areas and their sustainable use, including aspects such as water, wildlife, forests, the environment, soils, landscape, climate and recreation, as well as various other aspects relevant to the development and management of the environment we live in. Alterra engages in strategic and applied research to support design processes, policymaking and management at the local, national and international level. This includes not only innovative, interdisciplinary research on complex problems relating to rural areas, but also the production of readily applicable knowledge and expertise enabling rapid and adequate solutions to practical problems. The many themes of Alterra’s research effort include relations between cities and their surrounding countryside, multiple use of rural areas, economy and ecology, integrated water management, sustainable agricultural systems, planning for the future, expert systems and modelling, biodiversity, landscape planning and landscape perception, integrated forest management, geoinformation and remote sensing, spatial planning of leisure activities, habitat creation in marine and estuarine waters, green belt development and ecological webs, and pollution risk assessment. Alterra is part of Wageningen University and Research centre (Wageningen UR) and includes two research sites, one in Wageningen and one on the island of Texel. Geomorphological Change and River Rehabilitation Case Studies on Lowland Fluvial Systems in the Netherlands H.P. Wolfert ALTERRA SCIENTIFIC CONTRIBUTIONS 6 ALTERRA GREEN WORLD RESEARCH, WAGENINGEN 2001 This volume was also published as a PhD Thesis of Utrecht University Promotor: Prof. E.A. Koster Faculty of Geographical Sciences, Utrecht University Co-promotor: Dr J.A. Klijn Alterra, Wageningen University and Research centre Financial support for this thesis was given by The Ministry of Agriculture, Nature Management and Fisheries and by the Institute for Inland Water Management and Waste Water Treatment RIZA. ISBN 90-327-0311-0 CONTENTS Preface 11 1 General introduction 13 The context: river rehabilitation 13 Scope of the study: the functional-geographical approach 15 Study area: lowland river systems in the Netherlands 17 Aim, objectives and structure of the thesis 19 References 20 2 Functional-geographical approach 23 User requirements 23 Land resource inventory 23 Landforms and geomorphological processes 24 Functional hierarchies 26 Conclusions 28 References 28 3 Aquatic macrophyte growth and seasonal bedform pattern changes in a lowland sand-bed meandering stream 33 Introduction 34 Materials and methods 35 Physiography and hydrology 35 Study reach characteristics 36 Field surveys 38 Results 38 Discharge and macrophyte distribution 38 Bedform pattern characteristics 41 Bedform pattern dynamics 45 Discussion 51 Macrophyte–bedform interactions 51 Bedform classification and sediment exchange 53 Model for stream rehabilitation studies 53 Conclusions 55 References 56 4 Channel and bedform response to meander rehabilitation in lowland sand-bed streams 59 Introduction 60 Rehabilitation projects 61 Physiography and hydrology 61 Rehabilitation design 62 Monitoring programme 65 Results 66 Discharge events 66 Bank retreat 68 Cross-sectional change 69 Bedform development 74 Discussion 75 Initial adjustments 75 Role of design variables 77 Morphological and ecological diversity 78 Benefits of post-project appraisal 80 Conclusions 81 References 82 CONTENTS 5 The formation of natural levees as a disturbance process significant to theconservation of riverine pastures 85 Introduction 85 Materials and methods 87 Study area 87 Vegetation survey 89 Geomorphological survey 89 Results 90 Vegetation zonation and site factors 90 Floodplain geomorphology 91 Historical migration rates 93 Discussion 93 Disturbance model 93 Landform succession 95 Rehabilitation strategies 96 Conclusions 99 References 99 6 Variability in meandering of a lowland river controlled by bank composition 103 Introduction 103 Materials and methods 106 Study area 106 Geomorphological survey 106 Channel migration data 108 Results 109 River reaches and fluvial styles 109 Lateral erosion and accretion 113 Meander bend migration 118 Discussion 119 Significance of bank materials 119 Classification of erodibility 120 Application in river rehabilitation 122 Conclusions 124 References 124 7 Embanked river reaches in the River Rhine depositional zone – I. Historical geomorphology 127 Introduction 128 Materials and methods 129 Physiographical setting 129 Geomorphological maps 129 Hydrogeomorphological parameters 129 Results 133 Landform configuration 133 River reach dynamics 134 Channel and flow dimensions 139 Discussion 143 Landform succession 143 River metamorphosis 145 Fluvial style continuum 147 Conclusions 148 References 149 CONTENTS 8 Embanked river reaches in the River Rhine depositional zone – II. Rehabilitation planning 153 Introduction 154 Role of geomorphology 156 Rehabilitation policies 156 River ecosystem concepts 157 System classification and modelling 157 Rhine depositional zone 160 Historical reference situation 160 Suitability of river reaches 161 Rehabilitation measures 163 Gelderse Poort area 164 Rehabilitation scenarios 164 Impacts of fluvial processes 166 Feasibility of measures and effects 169 Discussion and conclusions 171 References 172 9 General discussion and conclusions 177 The functional-geographical approach 177 Geomorphological change: landform configurations and process variables 178 River rehabilitation: areas and design guidance 181 References 182 Summary 183 Samenvatting (summary in Dutch) 191 PREFACE AND ACKNOWLEDGEMENTS 11 Preface and acknowledgements This thesis is about geomorphological research for river rehabilitation purposes. My involvement in this work started with a memorable trip to the UK in November 1990, where I visited Ken Gregory, Andrew Brookes, Colin Thorne and Geoff Petts. During these visits I not only learned about the methods and perspectives of this type of research but also became infected with their enthusiasm. Since then many projects have been undertaken on small and large river systems and more recently on tidal rivers. As contract research, these probably would have been classified as applied geomorphology by university geomorphologists and as strategic research by those working for consulting agencies. Whatever it is called, to me, these studies are a very inspiring branch of science. Appealing aspects are the direct communication with stakeholders and the involvement of scientists from other disciplines. These types of cooperation often trigger original and challenging ideas worth examining in the research project at stake or valuable to the formulation of new, future studies. Besides, contract research guarantees a quick dissemination of results among those involved. However, there are also some disadvantages. Study results are published in reports, which are written in the Dutch language. This hampers communication with colleagues abroad and the involvement in transboundary or international projects. Moreover, the scientific novelties do not reach the audience they deserve. Therefore, I am very grateful that the opportunity arose to combine some of my geomorphological work on river rehabilitation planning into a thesis, of which the central chapters would be submitted to scientific magazines. Writing this thesis provided the opportunity to work out details as well as to place the various studies in a broader context. As usual in scientific studies, the cooperation of many individuals was indispensable. I would like to thank the following people: -Promotor Ward Koster, for guidance on this project and careful comments throughout the text; - Co-promotor Jan Klijn, for stimulating this work and continuous interest; -Gilbert Maas; Arjan Koomen, Margriet Schoor, Hans Middelkoop, Patrick Hommel, Diana Prins and Marleen Stam, for professional cooperation in the projects underlying this thesis and co-authors’ advice; -Bert Higler, Janrik van den Berg, Colin Thorne, Jef Vandenberghe, Bart Makaske, Hans Middelkoop, Henk Berendsen and Bert Harms, for valuable comments on drafts of one or more chapters; - Colin Thorne, Bob Bunce and Derek Middleton, for corrections to the English of 12 drafts or final versions of chapters; -Martin Jansen and Henk van Ledden, for design of the cover and drawing the excellent figures; - Co Onderstal and Gilbert Maas for making the coloured maps; -Mieke Pijfers for the lay-out of the thesis; -Bert Harms; Kees Hendriks, Eric Marteijn, Wilfried ten Brinke and Peter Smeets, for help with finding funds to carry on with this work; -Maja Kooistra, for temporarily being head of the Landscape Research Team to enable me to finishing writing this thesis; -Bart Makaske, Gilbert Maas, Bert Higler, Arjan Koomen, Sabine van Rooij, Jan Klijn, Chantal Kandhai and Monique Smaak, for temporarily taking over some of the other jobs at Alterra; -Piet Warmerdam, for hospitality, a room and desk at The Nieuwlanden office, where I wrote a large part of this thesis; - Lia Wolfert, Simon, Roel, Lise, Thomas, Jaap and Hanna, for support and patience at home and asking the most intriguing question of all: ‘Papa, wat hebben wij hier nou eigenlijk aan?’ (Dad, what is the use of all this to us?), which put this work into the right perspective. The writing of this thesis