Strategic Flood Risk Assessment 2019
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Elmbridge Borough Council Level 1 Strategic Flood Risk Assessment Elmbridge Borough Council Project number: 60565750 Final February 2019 Elmbridge Borough Council FINAL Level 1 Strategic Flood Risk Assessment Project number: 60565750 Quality information Prepared by Checked by Verified by Approved by Hannah Booth Sarah Littlewood Sarah Kelly Sarah Kelly Graduate Water Senior Consultant Regional Director Regional Director Consultant Amy Ruocco Peter Mansell Senior Consultant Technical Director Revision History Revision Revision date Details Authorized Name Position 1 Sep 2018 Draft 19/09/2018 Sarah Kelly Regional Director 2 Dec 2018 Final 05/12/2019 Emily Craven Associate 3 Feb 2019 Final amended 21/02/2019 Peter Mansell Technical Director 4. Sept 2019 Schedule added to 05/09/2019 Sarah Kelly Regional Director Appendix A Prepared for: Elmbridge Borough Council Prepared by: Hannah Booth AECOM Limited Midpoint, Alencon Link Basingstoke Hampshire RG21 7PP United Kingdom T: +44(0)1256 310200 aecom.com © 2019 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 Prepared for: Elmbridge Borough Council AECOM i Elmbridge Borough Council FINAL Level 1 Strategic Flood Risk Assessment Project number: 60565750 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. Prepared for: Elmbridge Borough Council AECOM ii Elmbridge Borough Council FINAL Level 1 Strategic Flood Risk Assessment Project number: 60565750 Table of Contents Abbreviations ............................................................................................................. v Glossary ..................................................................................................................... vi 1. Introduction and user guide ............................................................................. 8 1.1 Introduction ......................................................................................................................................... 8 1.2 Approach to Flood Risk Management .................................................................................................. 8 1.3 Purpose of the SFRA .......................................................................................................................... 9 1.4 Flood Risk Policy and Guidance ........................................................................................................ 10 1.5 User Guide ....................................................................................................................................... 11 1.6 Living Document ............................................................................................................................... 12 2. Methodology .................................................................................................. 13 2.1 Overview .......................................................................................................................................... 13 2.2 Consultation ...................................................................................................................................... 13 2.3 Data Collection.................................................................................................................................. 13 3. Assessing Flood Risk .................................................................................... 23 3.1 Overview .......................................................................................................................................... 23 3.2 Area ................................................................................................................................................. 23 3.3 Character .......................................................................................................................................... 24 3.4 Topography ....................................................................................................................................... 24 3.5 Geology ............................................................................................................................................ 24 3.6 Aquifers ............................................................................................................................................ 25 3.7 Groundwater Vulnerability.................................................................................................................. 25 3.8 Main Rivers ....................................................................................................................................... 25 3.9 Ordinary Watercourses ...................................................................................................................... 26 3.10 Flooding from Rivers ......................................................................................................................... 26 3.11 Flooding from Surface Water ............................................................................................................. 33 3.12 Flooding from Groundwater ............................................................................................................... 34 3.13 Flooding from Sewers ....................................................................................................................... 34 3.14 Flooding from Reservoirs................................................................................................................... 35 4. Avoiding Flood Risk ....................................................................................... 36 4.1 Sequential Approach ......................................................................................................................... 36 4.2 Applying Sequential Test – Plan-Making ............................................................................................. 36 4.3 Applying Sequential Test – Planning Applications ............................................................................... 40 4.4 Exception Test................................................................................................................................... 41 5. Managing and Mitigating Flood Risk .............................................................. 43 5.1 Overview .......................................................................................................................................... 43 5.2 Development Layout and Sequential Approach .................................................................................. 43 5.3 Finished Floor Levels ........................................................................................................................ 43 5.4 Flood Resistance ‘Water Exclusion Strategy’ ...................................................................................... 44 5.5 Flood Resilience ‘Water Entry Strategy’ ............................................................................................. 46 5.6 Safe Access and Egress .................................................................................................................... 47 5.7 Floodplain Compensation Storage ..................................................................................................... 48 5.8 Flood Routing ................................................................................................................................... 50 5.9 Riverside Development ..................................................................................................................... 50 5.10 Surface Water Management .............................................................................................................. 51 5.11 Flood Warning and Evacuation Plans ................................................................................................. 54 5.12 Flood Warning Areas and Emergency Rest Centres ........................................................................... 56 6. Guidance for Site-Specific FRAs ................................................................... 57 Prepared for: Elmbridge Borough Council AECOM iii Elmbridge Borough Council FINAL Level 1 Strategic Flood Risk Assessment Project number: 60565750 6.1 What is a Flood Risk Assessment? .................................................................................................... 57 6.2 When is a Flood Risk Assessment required? ...................................................................................... 57 6.3 How detailed should a FRA be? ......................................................................................................... 57 6.4 What needs to be addressed in a Flood Risk Assessment? ................................................................ 59 6.5 Flood Risk Assessment Checklist ...................................................................................................... 59 6.6 Pre-application Advice ....................................................................................................................... 62 7. Flood risk policy and development management