West Cornwall Catchment Flood Management Plan December 2008 Environment Agency West Cornwall Catchment Flood Management Plan - December 2008 We are the Environment Agency. It’s our job to look after your environment and make it a better place – for you, and for future generations. Your environment is the air you breathe, the water you drink and the ground you walk on. Working with business, Government and society as a whole, we are making your environment cleaner and healthier. The Environment Agency. Out there, making your environment a better place. Published by: Environment Agency Rio House Waterside Drive, Aztec West Almondsbury, Bristol BS32 4UD Tel: 01454 624400 Fax: 01454 624409 © Environment Agency December 2008 All rights reserved. This document may be reproduced with prior permission of the Environment Agency. Environment Agency West Cornwall Catchment Flood Management Plan - December 2008 Foreword I am pleased to introduce the West Cornwall Catchment Flood Management Plan. Past flood events remind us of the hardship that flooding can cause, especially in the built environment. They also reveal the challenges we face when confronted by the forces of nature. This plan will allow us to use a scientific approach to understand and describe how the catchment behaves and what the most sustainable flood risk management policies may be over the next 50 to 100 years. We can then use this direction to plan the most acceptable ways of managing flood risk for the long-term. We will use the catchment flood management plan to steer our future investment in flood risk management. We hope that our public and private partners will find it useful in their decision making, especially where it can guide the planning of land use. This plan will enable us to target our efforts and precious resources in the most beneficial way. Gordon Trapmore Cornwall Area Flood Risk Manager Environment Agency West Cornwall Catchment Flood Management Plan - December 2008 Contents List of Tables ..............................................................................................................................................iii List of Figures ............................................................................................................................................. v Executive Summary................................................................................................................................... vi 1. Introduction.......................................................................................................................................... 1 1.1 Background 1 1.2 Aims and scope 2 1.3 Policies 3 1.4 Links with other plans 4 1.5 Involving others 7 2. Catchment overview.......................................................................................................................... 11 2.1 Definition and extent of the West Cornwall catchment 11 2.2 Topography 16 2.3 Geology and Hydrogeology 18 2.4 Geomorphology 20 2.5 Soils 21 2.6 Land use and land management 23 2.7 Hydrology 28 2.8 Environment and heritage 36 2.9 Communities and the local economy 48 3. Current flood risks and management ................................................................................................ 50 3.1 History of flooding 50 3.2 Sources and probability of flooding 54 3.3 Consequences of flooding 66 3.4 Summary of flood risk 86 3.5 Existing flood risk management 89 4. Future flood risk............................................................................................................................... 101 4.1 Introduction 101 4.2 Future scenarios 102 4.3 Assessment of future flood risk 108 4.4 Summary of flood risk at key sites 126 5. Catchment Objectives ..................................................................................................................... 128 5.1 Introduction 128 5.2 Catchment opportunities and constraints 128 5.3 CFMP objectives 128 6. Policy Appraisal............................................................................................................................... 139 6.1 Introduction 139 6.2 Policies for the West Cornwall CFMP area 140 7. Implementing the CFMP.................................................................................................................. 159 7.1 Action plan 159 7.2 Consequences of our actions 211 7.3 Monitoring, review and evaluation 213 Glossary of terms.................................................................................................................................... 215 List of abbreviations................................................................................................................................ 224 References ............................................................................................................................................. 226 Environment Agency i West Cornwall Catchment Flood Management Plan - December 2008 Bibliography............................................................................................................................................ 229 Appendix A - Responsibilities for Flood Risk Management .................... AError! Bookmark not defined. Appendix B - Environmental Report .........................................................................................................B1 Appendix C - Main River Map.................................................................. CError! Bookmark not defined. Appendix D - Consultation responses ..................................................... DError! Bookmark not defined. Appendix E - Appropriate Assessment (Form HR01).............................. EError! Bookmark not defined. Appendix F - Appropriate Assessment (Form HR02).............................. FError! Bookmark not defined. Appendix G - West Cornwall Habitat Impacts…………………………………………………………………G1 Appendix H - Water Framework Directive compliance check……………………………………………….H1 Environment Agency ii West Cornwall Catchment Flood Management Plan - December 2008 List of Tables Table 1.1 Flood Risk Management policies........................................................................... 4 Table 1.2 Key consultation issues and comments ................................................................ 8 Table 1.3 Consultation Stages............................................................................................... 9 Table 2.1 Key Parameters for a number of Main River catchments.................................... 14 Table 2.2 Land use within the catchment ............................................................................ 25 Table 2.3 Land Grade within the catchment and the 1 per cent a.p or 0.5 per cent a.p flood extent.................................................................................................................. 26 Table 2.4 Population centres and distribution within the catchment.................................... 27 Table 2.5 Watercourse response......................................................................................... 35 Table 2.6 Condition of SSSIs within the 1 per cent a.p or 0.5 per cent a.p flood extent (November 2006)................................................................................................ 39 Table 2.8 River Quality Objectives (2000) ........................................................................... 44 Table 3.1 Historic flood events............................................................................................. 52 Table 3.2 Sources of flooding .............................................................................................. 55 Table 3.3 People at risk of flooding at key sites in West Cornwall ...................................... 67 Table 3.4 Percentage of residents affected by flooding and speed of flooding onset ......... 68 Table 3.5 Depth of flooding at key sites............................................................................... 70 Table 3.6 Velocity of flooding at key sites............................................................................ 71 Table 3.7 Maximum flood hazard at key sites ..................................................................... 72 Table 3.8 Social vulnerability ............................................................................................... 73 Table 3.9 Economic flood damages for key sites – Annual Average Damages.................. 77 Table 3.10a Estimated commercial and residential damages from a 10 per cent a.p. flood event................................................................................................................... 78 Table 3.10b Estimated commercial and residential damages from a 1 per cent a.p. (fluvial) 0.5 per cent a.p. (tidal) Event ............................................................................. 78 Table 3.10c Estimated commercial and residential damages from a 0.1 per cent a.p. flood event................................................................................................................... 79 Table 3.11 Total estimated damages..................................................................................... 81 Table 3.12 Critical infrastructure affected by flooding............................................................ 82 Table 3.13 Economic damages related to other flooding ...................................................... 83 Table 3.14 Designated sites within the 1 per cent or 0.5 per cent a.p. flood extent.............. 84 Table 3.15 Summary of flood risk at key