South Gloucestershire Council Strategic Flood Risk Assessment - Level 2 FINAL REPORT December 2011 South Gloucestershire Council Council Offices Badminton Road YATE Gloucestershire BS37 5AF JBA Office Aberdeen House South Road HAYWARDS HEATH West Sussex RH16 4NG JBA Project Manager Alastair Dale BSc PGDip MIAHR Revision History Revision Ref / Amendments Issued to Date Issued Pam Walton (South Gloucestershire V1.0 - First Draft N/A Council) (July '11) Nigel Smith (EA) Pam Walton (South Gloucestershire V1.1 - Updated Updated with initial comments from client Council) Draft and EA Nigel Smith (EA) at meeting dated the 30 August 2011 ( Hard Copy) Updated following meeting on the 30 August 2011, Comments from EA 05/08/2011 and 26/08/2011 V 2.0 Updated Not Issued Comments from SGC 26/08/2011, 02/09/2011 and 07/09/2011 Updated following emails dated Pam Walton (South Gloucestershire 7 September (EA) Council) V3.0 - FINAL 14 September 2011 (SGC) Nigel Smith (EA) DRAFT 23 September (EA) Nigel Hale (South Gloucestershire 28 September (SGC) Council 03 October (SGC) Updated following emails from SGC on the: Pam Walton (South Gloucestershire 27 October, 28 October, 31 October, 4 Council) November, 8 November and the 9 V4.0 FINAL Nigel Smith (EA) November. Nigel Hale (South Gloucestershire And from the EA on the Council 25 October, 4 November Pam Walton (South Gloucestershire Council) Update following emails dated: v5.0 FINAL Nigel Smith (EA) 2/12/2011 (SGC) Nigel Hale (South Gloucestershire Council Pam Walton (South Gloucestershire Council) Update following dated V6.0 FINAL Nigel Smith (EA) 6/12/2011 (SGC) Nigel Hale (South Gloucestershire Council Pam Walton (South Gloucestershire Council) Update following email dated V7.0 Final Nigel Smith (EA) 6 /12/2011 (SGC) Nigel Hale (South Gloucestershire Council 2011s4997 SGC FINAL SFRA Level 2 v7.0.doc i 2011s4997 SGC FINAL SFRA Level 2 v7.0.doc ii Contract This Level 2 Strategic Flood Risk Assessment (SFRA) is commissioned by South Gloucestershire Council. This document has been prepared by JBA Consulting in response to the Level 2 SFRA commission awarded by South Gloucestershire Council, in March 2011. Prepared by .................................................. Jack Southon BSc MSc FRGS Analyst ....................................................................... Margaret Moran LLM BSc Dip Analyst Reviewed by ................................................. Alastair Dale BSc PGDip MIAHR Technical Director Purpose This document has been prepared as a report for South Gloucestershire Council. JBA Consulting accepts no responsibility or liability for any use that is made of this document other than by South Gloucestershire Council for the purposes for which it was originally commissioned and prepared. 2011s4997 SGC FINAL SFRA Level 2 v7.0.doc iii Copyright © Jeremy Benn Associates Limited 2011 Carbon Footprint 367g A printed copy of the main text in this document will result in a carbon footprint of 289g if 100% post-consumer recycled paper is used and 367g if primary-source paper is used. These figures assume the report is printed in black and white on A4 paper and in duplex. JBA is aiming towards becoming a carbon neutral company and the carbon emissions from our activities are offset. 2011s4997 SGC FINAL SFRA Level 2 v7.0.doc iv This page is intentionally blank. 2011s4997 SGC FINAL SFRA Level 2 v7.0.doc v Contents Abbreviations and Glossary of Terms ............................................................................ x 1. Introduction ........................................................................................................... 1 1.1 About this Report .................................................................................................... 1 1.2 SFRA Objectives .................................................................................................... 2 1.3 How to Find What You Need in the SFRA ............................................................. 3 1.4 Scope of Assessment ............................................................................................. 4 1.5 Approach ................................................................................................................ 7 1.6 Consultation ............................................................................................................ 8 2. Understanding Flood Risk in South Gloucestershire ...................................... 9 2.1 Historic Flooding ..................................................................................................... 9 2.2 Topography, Geology, Soils and Hydrology .......................................................... 9 2.3 Bristol Avon Catchment .......................................................................................... 10 2.4 Severn Tidal Catchment ......................................................................................... 17 2.5 How Flood Risk is Assessed .................................................................................. 19 2.6 Understanding Flooding in South Gloucestershire ................................................ 23 2.7 Possible Responses to Flooding ............................................................................ 25 2.8 Policy Considerations ............................................................................................. 26 3. Mapping and Risk Based Approach ................................................................... 31 3.1 Summary of Mapping for All Sources of Flood Risk .............................................. 31 3.2 Other Relevant Flood Risk Information .................................................................. 32 3.3 Sequential Approach .............................................................................................. 33 3.4 Sequential Test ....................................................................................................... 33 3.5 Exception Test ........................................................................................................ 36 4. Overview of Future Development ....................................................................... 37 4.1 Extent and type of development ............................................................................. 37 4.2 Review of Future Development .............................................................................. 38 4.3 Summary of Existing Surface Water Regime ......................................................... 40 5. Strategic Assessment of Future Development ................................................. 43 5.1 Introduction ............................................................................................................. 43 5.2 Development over the next 5 Years ....................................................................... 43 5.3 Longer Term Development up to 2026 .................................................................. 46 5.4 Approach to Analysis of Catchment Response to Development ........................... 47 6. Catchment Response to Development .............................................................. 51 6.1 Introduction ............................................................................................................. 51 6.2 Key Locations ......................................................................................................... 51 6.3 Summary of Existing Situation ............................................................................... 51 6.4 Establishing a Baseline .......................................................................................... 52 6.5 Guidance on SuDS Techniques ............................................................................. 55 7. Strategic Options.................................................................................................. 57 7.1 Possible Strategic Options ..................................................................................... 57 7.2 Review and Assessment of Options ...................................................................... 57 7.3 Indicative Costs and Scale ..................................................................................... 68 7.4 Conclusions ............................................................................................................ 68 2011s4997 SGC FINAL SFRA Level 2 v7.0.doc vi 8. Summary Assessment of Core Strategy Development Sites .......................... 69 8.1 Introduction ............................................................................................................. 69 8.2 Summary Tables and Maps ................................................................................... 69 9. FRA Requirements ............................................................................................... 71 9.1 Over-Arching Principles .......................................................................................... 71 9.2 Requirements for Flood Risk Assessments ........................................................... 71 10. Outcomes .............................................................................................................. 73 10.1 Summary of Work Undertaken ............................................................................... 73 10.2 Outcomes ............................................................................................................... 73 Appendices .......................................................................................................................