Defra/Environment Agency Flood and Coastal Defence R&D Programme Guidebook of Applied Fluvial Geomorphology R&D Technical Report FD1914 Defra/Environment Agency Flood and Coastal Defence R&D Programme Guidebook of Applied Fluvial Geomorphology R&D Technical Report FD1914 Photo Courtesy of the Northern Echo Authors: David A. Sear, Malcolm D. Newson, and Colin R. Thorne Publishing organisation Defra Flood Management Division Ergon House 17 Smith Square London SW1P 3JR Tel: 020 7238 6178 Fax: 020 7238 6187 www.defra.gov.uk/environ.fcd ISBN: 0-85521-053-2 © Crown Copyright (Defra), December 2003 Copyright in the typographical arrangement and design rests with the Crown. This publication (excluding the logo) may be reproduced free of charge in any format or medium provided that it is reproduced accurately and not used in a misleading context. The material must be acknowledged as Crown copyright with the title and source of the publication specified. The views expressed in this document are not necessarily those of Defra or the Environment Agency. Its officers, servants or agents accept no liability whatsoever for any loss or damage arising from the interpretation or use of the information, or reliance on views contained herein. Dissemination Status Internal: Released Internally External: Publicly Available Statement of use This document provides guidance to Defra and Environment Agency staff, research contractors and external agencies on the use of fluvial geomorphology in river management within the UK. Keywords Fluvial Geomorphology, Sediment transfer, Enviromental Impact, Erosion Research contractor Nottingham University Consultants Ltd, University Park, Nottingham NG7 2RD. Defra Project Officer Mr M Thorn, Wallingford Research Consultancy, 18 Thames Mead, Crowmarsh Gifford, Wallingford, Oxfordshire OX10 8EX. Email: [email protected] R&D TECHNICAL REPORT FD1914 CONTENTS Preface ix Purpose of the Guidebook ix Basis for the Guidebook ix Inventory of sources used in preparing the Guidebook xiv 1. Fluvial Geomorphology: Its basis and methods 1 1.1 Introduction 1 1.2 What is Geomorphology and what is it not? 1 1.3 Expertise and expectation in consulting geomorphologists 2 1.4 What is the contribution of Fluvial Geomorphology to river management? 3 1.5 Costs and Benefits of using fluvial geomorphology in river management 6 1.6 Performance Testing Fluvial Geomorphology 11 1.7 Geomorphology and sustainability 13 1.8 What are Geomorphological timescales? 13 1.9 What are Geomorphological data? 19 1.10 Procedures for the collection and interpretation of geomorphological data 29 Appendix 1.1 Points of contact for further information on fluvial geomorphology 34 2 River processes and channel geomorphology 36 2.1 Introduction to the chapter 36 2.2 River channel form: the basic drivers 36 2.3 The river catchment sediment system 39 2.4 Sediment storage in rivers 41 2.5 Sediment transport in rivers 43 2.6 Channel adjustment: concepts of change 44 2.7 River channel geomorphology 47 2.8 The role of river classification and typology in river management 78 3 Driving processes 1: Understanding river sediment dynamics 80 3.1 Introduction 80 3.2 Fluvial Processes 81 3.3 The Sediment Transfer System 113 R&D TECHNICAL REPORT FD1914 i 4. Driving Processes 2: Characterising and managing river sediment dynamics 128 4.1 Geomorphological Studies 128 4.2 Managing Sediment-Related Problems 138 4.3 Managing Sediment Transfers – Sediment Traps 146 4.4 Managing Deposition 150 4.5 Catchment Approach to Sediment Management 153 4.6 Briefs for Geomorphological Studies 154 5. Geomorphology and river ecosystems: Tools and strategies for river and floodplain management 167 5.1 Introduction 167 5.2 ‘Fluvial hydrosystems’ 167 5.3 Channel-floodplain interactions 169 5.4 River and riparian habitats – geomorphology and River Habitat Surveys 173 5.5 Fluvial geomorphology and river restoration 178 5.6 Conclusions 184 6. Case studies of the application of geomorphological assessment procedures 186 6.1 Introduction - geomorphological assessment, information and guidance. 186 6.2 Dimensions of the review 187 6.3 Sources 189 6.4 Analysis 192 6.5 Recent trends in geomorphological assessment projects 195 6.6 Recent geomorphological extension of River Habitat Surveys 200 6.7 Geomorphological assessment - conclusions 202 APPENDIX 6.1: Review of case studies used in the development of Fluvial Audit procedures by Sear and Newson (1994) 204 APPENDIX 6.2:Training course and training materials 215 References 220 R&D TECHNICAL REPORT FD1914 ii LIST OF FIGURES Figure 1 Geomorphological Knowledge x Figure 2 Applications of Geomorphology xi Figure 3 New Materials Required xii Figure 1.1 When to Consider Geomorphology in River Management 4 Figure 1.2 Indicative Sediment storage time in the river landscape (after Brown, 1987) 14 Figure 1.3 The significance of timescale in applying fluvial geomorphology to river channel management; Meander cut-off processes on the River Endrick. 15 Figure 1.4 Time and spatial scales in the formation of UK River landscapes, (after Knighton, 1984). 15 Figure 1.5 The concept of equilibrium in Fluvial Geomorphology. 17 Figure 1.6 Channel planform change following extreme flooding in an upland river illustrating the natural recovery of the former channel planform; Dorback Burn, Scotland (Werrity, 1984). 18 Figure 1.7 Types and scales of data used in Fluvial Geomorphological Asssesment 21 Figure 1.8 Information on historical river planform change derived from overlaying large scale maps. 22 Figure 1.9aExample of fluvial geomorphologial data capture in a catchment scale survey (GeoData Institute) 24 Figure 1.9bExample of fluvial geomorphological data capture at the reach scale 24 Figure 1.10Bank stability assessment for a bank erosion problem. Data is based on the analysis of cross-sections supported by ground- truthing through field reconnaissance to identify eroding and stable bank profiles; River Sence, Leicestershire. 26 Figure 1.11An example of channel incision revealed by exposure of a former river bed level in the bank material. Incision in this instance was a result of a land drainage scheme. 28 Figure 2.1 Independent and dependent controls on channel form (after Thorne, 1997). 36 Figure 2.2 A conceptual model of the feedback between channel form, flow, sediment transport and grainsize after Ashworth & Ferguson 1986) 38 Figure 2.3 Links between the different scales of river geomorphology (after Sear 1996). 41 Figure 2.4 Sediment connectivity in the fluvial system (after Newson & Sear 1993). 42 Figure 2.5 Drainage Networks: a) Geological controls on regional drainage networks and b) geological controls on drainage network; River Kennet catchment, UK (courtesy of GeoData Institute). 51 R&D TECHNICAL REPORT FD1914 iii Figure 2.6 Valley form and its control on connectivity between the catchment surface and the river network. 52 Figure 2.7 The long profile of a river; illustrating geological and base level controls on valley gradient. 53 Figure 2.8 a) High-energy floodplain; b) high-moderate energy alluvial floodplain, c) Low energy floodplain; d) Forested floodplain 54 Figure 2.9 The hierarchy of scales in the river system 57 Figure 2.10The 3-Dimensions of river channel form 59 Figure 2.11Variation in channel width as a result of bank material and hydrology (after Dangerfield, 1999) 60 Figure 2.12Definitions of channel planform (after Rust, 1978). 61 Figure 2.13The role of alternate bars in the development of meandering in alluvial rivers (after Lewin, 1976). 62 Figure 2.14Variables used in the definition of meander bend geometry (after Thorne, 1997). 63 Figure 2.15Secondary flow structure in a meander bend and its relationship with scour the form of the channel cross-section. 64 Figure 2.16Braided River Reach; River Swale, Yorkshire. Note multiple channels flowing between active gravel shoals within a channel bounded by a vegetated and elevated floodplain surface. 65 Figure 2.17Downstream hydraulic geometry 68 Figure 2.18A sedimentation zone on the River South Tyne, Northumberland (Photo courtesy of Northern Echo). 70 Figure 2.19Some typical sediment deposits in UK rivers: a) Chaotic boulder channel b) tributary confluence bar, c) Mid channel bar, d) point bar e) side bar f) fine sediment berm 71 Figure 2.20Variations in the local long profile: a) Step Pool sequence in steep coarse sediment channels and b) Riffle-pool sequence in alluvial cobble and gravel-bedded rivers. 73 Figure 2.21A classification of debris dams and their relationship to channel morphology (after Hogan et al. 1998). 77 Figure 3.1 Links and interactions between sediment processes and fluvial landforms 82 Figure 3.2 Commonly observed modes of bank failure 93 Figure 3.2 Commonly observed modes of bank failure 94 Figure 3.3 Sediment fluxes in the near bank zone 96 Figure 3.4 Types of Adjustment commonly observed in Unstable Channels 98 Figure 3.5 50-year record of gravel yield (in-trap accumulation) in a gravel trap on Coledale Beck in the Lake District. Arrows indicate occurrence of flood events. 100 Figure 3.6 Storm hydrograph and sediment hydrograph showing pulses of bedload movement out of phase with variation in stream flow. 101 R&D TECHNICAL REPORT FD1914 iv Figure 3.7 Typical channel bars observed in gravel and cobble-bed rivers with active bedload transport 108 Figure 3.8 Distributions of surface and near-bed flow, and bedload transport in meandering channel 109 Figure 3.9 Contemporary erosion and sedimentation in the middle course associated with: a) sediment exchange and lateral