South Essex Level 1 Strategic Flood Risk Assessment (SFRA)
Total Page:16
File Type:pdf, Size:1020Kb
South Essex Level 1 Strategic Flood Risk Assessment Final Report April 2018 Project Number: 60532482 60532482 Final Report April 2018 AECOM South Essex Level 1 Strategic Flood Risk Assessment Page i Quality information Prepared by Checked by Approved by Hannah Booth Sarah Kelly Carl Pelling Graduate Water Consultant Regional Director Associate Joanna Bolding Hydrology Consultant Amy Ruocco Senior Consultant Revision History Revision Revision date Details Authorized Name Position v1 November 2017 Draft for Comment 03/11/2017 Sarah Kelly Regional Director v2 April 2018 Final 27/04/2018 Carl Pelling Associate Director Prepared for: Basildon Borough Council, Castle Point Borough Council, Rochford District Council, Southend-on-Sea Borough Council, and Essex County Council. AECOM Limited Midpoint Alencon Link Basingstoke Hampshire RG21 7PP UK T: +44(0)1256 310200 aecom.com © 2018 AECOM Limited. All Rights Reserved. This document has been prepared by AECOM Limited (“AECOM”) for sole use of our client (the “Client”) in accordance with generally accepted consultancy principles, the budget for fees and the terms of reference agreed between AECOM and the Client. Any information provided by third parties and referred to herein has not been checked or verified by AECOM, unless otherwise expressly stated in the document. No third party may rely upon this document without the prior and express written agreement of AECOM. 60532482 Final Report April 2018 AECOM South Essex Level 1 Strategic Flood Risk Assessment Page ii Table of Contents Glossary of Terms ............................................................................................................................................ v Executive Summary ........................................................................................................................................ vii 1. Introduction .......................................................................................................................................... 1 2. Level 1 SFRA Methodology.................................................................................................................... 8 3. Climate Change ................................................................................................................................... 16 4. Flood Risk in the Basildon Borough ...................................................................................................... 19 5. Flood Risk in Castle Point .................................................................................................................... 28 6. Flood Risk in Rochford District ............................................................................................................. 35 7. Flood Risk in the Southend-On-Sea Borough ....................................................................................... 42 8. Guidance for the application of the Sequential Test.............................................................................. 50 9. Guidance for Managing and Mitigating Flood Risk ................................................................................ 59 10. Guidance for the Application of Sustainable Drainage Systems ........................................................... 68 11. What is a Flood Risk Assessment? ....................................................................................................... 75 12. Next Steps .......................................................................................................................................... 82 Appendix A Figures ........................................................................................................................................ 84 Appendix B - Flood Risk Policy and Development Management Considerations .............................................. 85 Appendix C Prittle Brook Climate Change Modelling ....................................................................................... 91 Appendix D South Essex Breach Modelling Methodology ............................................................................... 94 Appendix E South Essex Breach Mapping ..................................................................................................... 102 Figures Figure 1-1 Taking flood risk into account in the preparation of a Local Plan.................................................................... 3 Figure 8-1 Application of Sequential Test for Local Plan preparation – Undefended sites ........................................52 Figure 8-2 Application of Sequential Test for Local Plan preparation – Tidal defended sites....................................53 Figure 9-1 Flood Resistant / Resilient Design Strategies, Improving Flood Performance, DCLG 2007 ..................61 Tables Table 3-2 Fluvial Flood Zones (extracted from the NPPG, 2014) ......................................................................................... 9 Table 3-7 Hazard categories based on FD2320, Defra & Environment Agency 2005 .................................................11 Table 4-1 Basildon breach names and modelling parameters ...........................................................................................20 Table 4-2 Basildon Washlands Storage Areas (from Basildon SFRA 2011) ....................................................................21 Table 4-3 Ordinary watercourse in Basildon Borough..........................................................................................................24 Table 4-4 Summary of past flood events in Basildon ...........................................................................................................26 Table 5-1 Castle Point breach names and modelling parameters ....................................................................................29 Table 5-3 Summary of past flood events in Castle Point ....................................................................................................34 Table 6-1 Rochford breach names and modelling parameters .........................................................................................36 Table 6-2 Emergency Rest Centres in the Rochford District ..............................................................................................38 Table 6-3 Summary of past flood events in Rochford ..........................................................................................................40 Table 7-1 Southend-on-Sea breach names and modelling parameters .........................................................................43 Table 7-2 Emergency Rest Centres in the Southend-On-Sea Borough ..........................................................................45 Table 7-3 Summary of past flood events in Southend-On-Sea ........................................................................................47 Table 8-1 Flood Risk Management Hierarchy and the SFRA Process .............................................................................50 Table 8-2 Flood Risk Definitions for Sequential Test ............................................................................................................51 Table 8-3 Flood Risk Vulnerability Classification (PPG, 2014) ............................................................................................54 Table 8-4 Flood Risk Vulnerability and Flood Zone ‘Compatibility’ (PPG, 2014) ............................................................55 Table 9-1 Finished Floor Levels for fluvial flood risk areas .................................................................................................60 Table 9-2 Hazard to People Rating (HR=d x (v +0.5) + DF) ...................................................................................................63 Table 10-1 Typical SuDS Components (Y; primary process. * some opportunities, subject to design) .................69 Table 10-4 Suitability of Infiltration SuDS for each Borough/District ...............................................................................73 Table 10-5 Levels of Site specific Flood Risk Assessment ................................................................................................76 Table 10-6 Site specific Flood Risk Assessment Checklist (building on guidance in PPG) ........................................78 60532482 Final Report April 2018 AECOM South Essex Level 1 Strategic Flood Risk Assessment Page iii 60532482 Final Report April 2018 AECOM South Essex Level 1 Strategic Flood Risk Assessment Page iv Abbreviations ACRONYM DEFINITION AEP Annual Exceedance Probability AIMS Asset Information Management System AOD Above Ordnance Datum AStGWF Areas Susceptible to Groundwater Flooding AStSWF Areas Susceptible to Surface Water Flooding AWS Anglian Water Services BGS British Geological Survey CDA Critical Drainage Area CFMP Catchment Flood Management Plan Defra Department for Environment, Flood and Rural Affairs DCLG Department for Communities and Local Government ECC Essex County Council E&SW Essex and Suffolk Water FMfSW Flood Map for Surface Water FRA Flood Risk Assessment FRMP Flood Risk Management Plan FWMA Flood and Water Management Act 2010 GIS Geographical Information System IUD Integrated Urban Drainage LFRMS Local Flood Risk Management Strategy LiDAR Light Detection and Ranging LLFA Lead Local Flood Authority LPA Local Planning Authority LRF Local Resilience Forum NPPF National Planning Policy Framework PFRA Preliminary Flood Risk Assessment PPG Planning Practice