Strategic Flood Risk Assessment July 2021
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Level 1 Strategic Flood Risk Assessment 60616914 Level 1 Strategic Flood Risk Assessment Basingstoke and Deane Borough Council Project number: 60616914 July 2021 Level 1 Strategic Flood Risk Assessment 60616914 Quality information Prepared by Checked by Verified by Approved by Hannah Booth Sarah Littlewood Emily Craven Bernadine Maguire Graduate Water Consultant Principal Consultant Associate Principal Flood Risk & Coastal Consultant Revision History Revision Revision date Details Authorized Name Position 1 March 2020 Draft Report EC Emily Craven Associate 2 August 2020 Final Draft Report EC Emily Craven Associate 3 April 2021 Final Report BM Bernadine Maguire Principal 4 July 2021 Final Report BM Bernadine Maguire Principal Prepared for: Basingstoke and Deane Borough Council Prepared by: AECOM Limited Midpoint, Alencon Link Basingstoke Hampshire RG21 7PP United Kingdom T: +44(0)1256 310200 aecom.com Reference: 60616914 © 2021 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. Prepared for Basingstoke and Deane Borough Council AECOM July 2021 Level 1 Strategic Flood Risk Assessment 60616914 Table of Contents User Guide ................................................................................................................... i Abbreviations .............................................................................................................. ii Glossary of Terms ...................................................................................................... iii 1. Introduction ...................................................................................................... 5 1.1 Terms of Reference .................................................................................................................... 5 1.2 Study Area .................................................................................................................................. 5 1.3 Constraints on Development due to Protected Areas ................................................................. 7 2. Planning Policy and Guidance ......................................................................... 8 2.1 Policy and Local Context ............................................................................................................ 8 2.2 Approach to Flood Risk Management....................................................................................... 10 2.3 SFRA Level 1 and 2 .................................................................................................................. 11 3. Study Methodology ........................................................................................ 13 3.1 Methodology ............................................................................................................................. 13 3.2 Stakeholder Engagement ......................................................................................................... 13 4. Level 1 SFRA ................................................................................................. 16 4.1 Flooding from Rivers................................................................................................................. 16 4.2 Flooding from Surface Water .................................................................................................... 21 4.3 Flooding from Sewers ............................................................................................................... 24 4.4 Flooding from Groundwater ...................................................................................................... 25 4.5 Flooding from Artificial Sources ................................................................................................ 29 4.6 Localised Flooding Areas .......................................................................................................... 30 4.7 Planned Development Areas .................................................................................................... 30 4.8 Cumulative Impact of Development and Land-use Change...................................................... 30 5. Flood Risk Management Measures ................................................................ 33 5.1 Strategic Flood Risk Management ............................................................................................ 33 5.2 Current Flood Management Measures ..................................................................................... 33 5.3 Future Flood Management ....................................................................................................... 37 5.4 Mitigation Measures.................................................................................................................. 38 6. Policy Recommendations ............................................................................... 39 7. Summary and Next Steps .............................................................................. 41 7.1 Summary .................................................................................................................................. 41 7.2 Next Steps ................................................................................................................................ 41 Appendix A Data register .......................................................................................... 42 Appendix B Flood Risk Maps .................................................................................... 45 Figure 1- Topography and Watercourses Figure 2- Bedrock Geology and Superficial Deposits Figure 3 and Figures 3a-3e- Risk of flooding from rivers Figure 4a-4b River Enborne- Risk of flooding including the impact of Climate Change Figure 4c- River Loddon- Risk of flooding including the impact of Climate Change Figure 5- Historic Flooding Figures 6a-6e- Risk of Flooding from Surface Water Figure 7a- Sewer Flooding- External Figure 7b- Sewer Flooding- Internal Figure 8- Susceptibility to Groundwater Flooding Figure 9- Flood Warning and Flood Alert Areas Figure 10- Suitability for Infiltration SuDS Prepared for Basingstoke and Deane Borough Council AECOM July 2021 Level 1 Strategic Flood Risk Assessment 60616914 Appendix C Applying the Sequential Test and Exception Test in the preparation of a Local Plan ...................................................................................................... 46 C.1 Overview ................................................................................................................................... 46 C.2 Applying the Sequential Test for the Local Plan ........................................................................ 46 C.3 Windfall Sites ............................................................................................................................ 50 C.4 Level 2 SFRA ........................................................................................................................... 50 C.5 Exception Test .......................................................................................................................... 50 Appendix D The Sequential Test and Exception Test for planning applications ........ 52 D.1 Applying the Sequential Test for Planning Applications ............................................................ 52 D.2 Sequential Test Exemptions ..................................................................................................... 52 D.3 Exception Test .......................................................................................................................... 53 Appendix E Site Specific Flood Risk Assessments ................................................... 54 E.1 What is a Flood Risk Assessment? .......................................................................................... 54 E.2 When is a Flood Risk Assessment required? ........................................................................... 54 E.3 How detailed should a FRA be? ............................................................................................... 54 E.4 Statutory and non-statutory consultees for flood risk issues ..................................................... 55 E.5 What needs to be addressed in a Flood Risk Assessment? ..................................................... 57 Appendix F Mitigation Measures ............................................................................... 61 F.1 Guidance documents ................................................................................................................ 61 F.2 Development Layout and Sequential Approach ........................................................................ 61 F.3 Finished Floor Levels................................................................................................................ 61 F.4 Flood Resistance ‘Water Exclusion Strategy’ ........................................................................... 62 F.5 Flood Resilience ‘Water Entry Strategy’ ..................................................................................