Strategic Flood Risk Assessment
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Jersey Strategic Flood Risk Assessment Government of Jersey Project number: 60627145 April 2021 Jersey Strategic Flood Risk Assessment AECOM Project Number: 60627145 Quality information Prepared by Checked by Verified by Approved by Hannah Booth Sarah Littlewood Emily Craven Bernadine Maguire Graduate Water Principal Flood Risk Associate Principal Flood Risk & Consultant Consultant Coastal Consultant Bernadine Maguire Principal Flood Risk & Coastal Consultant Revision History Revision Revision date Details Authorized Name Position 1 April 2020 Draft for comment BM Bernadine Maguire Principal 2 December 2020 Final draft BM Bernadine Maguire Principal 3 January 2021 Final BM Bernadine Maguire Principal 4 March 2021 Final BM Bernadine Maguire Principal 5 April 2021 Final BM Bernadine Maguire Principal Prepared for: Government of Jersey Prepared by: AECOM Infrastructure & Environment UK Limited Midpoint, Alencon Link Basingstoke Hampshire RG21 7PP United Kingdom T: +44(0)1256 310200 aecom.com © 2021 AECOM Infrastructure & Environment UK Limited. All Rights Reserved. This document has been prepared by AECOM Infrastructure & Environment UK 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. AECOM Jersey Strategic Flood Risk Assessment AECOM Project Number: 60627145 Table of Contents User Guide ............................................................................................................................. i 1. Introduction................................................................................................................ 1 1.1 Study area overview .............................................................................................................. 1 2. Island Plan Review .................................................................................................... 3 2.1 Island Plan ............................................................................................................................ 3 3. Methodology .............................................................................................................. 6 3.1 Overview ............................................................................................................................... 6 3.2 Understanding flood risk ........................................................................................................ 6 3.3 Actual and residual risk .......................................................................................................... 8 3.4 Data collection ....................................................................................................................... 8 3.5 Assessing each source of flooding ......................................................................................... 9 4. Flood risk overview .................................................................................................. 12 4.1 Coastal flooding................................................................................................................... 12 4.2 Inland flooding ..................................................................................................................... 16 4.3 Reservoir flooding................................................................................................................ 24 4.4 Sewer Flooding ................................................................................................................... 27 4.5 Summary ............................................................................................................................ 28 5. Flood risk mitigation measures in Jersey ................................................................. 29 5.1 Current flood risk management measures ............................................................................ 29 5.2 Future flood risk management measures .............................................................................. 33 6. Strategic flood risk management ............................................................................. 38 6.1 Flood storage areas ............................................................................................................. 38 6.2 Catchment and floodplain restoration ................................................................................... 39 6.3 Upstream natural catchment management methods ............................................................. 40 6.4 Opportunities for strategic flood risk management in Jersey .................................................. 41 7. Flood risk framework ............................................................................................... 42 7.1 Overview ............................................................................................................................. 42 7.2 Flood risk categories............................................................................................................ 42 7.3 Vulnerability classifications................................................................................................... 43 7.4 Development suitability and planning approach .................................................................... 45 8. Site specific flood risk management measures ........................................................ 47 8.1 Site measures ..................................................................................................................... 47 8.2 Building measures ............................................................................................................... 51 9. Cumulative development and land use change ....................................................... 55 9.1 Cumulative impacts ............................................................................................................. 55 9.2 Land-use change ................................................................................................................. 55 10. Recommendations for policy and guidance ............................................................. 56 10.1 Overview ............................................................................................................................. 56 10.2 Guidance ............................................................................................................................ 56 Appendix A Data Register ................................................................................................... 57 Appendix B Maps ................................................................................................................ 60 Appendix C Pumping Station Catchment Areas .................................................................. 61 Appendix D Site Specific Flood Risk Assessments ............................................................. 62 D.1 What is a Flood Risk Assessment?....................................................................................... 62 D.2 When is a FRA required? ..................................................................................................... 62 D.3 What should a FRA contain? ................................................................................................ 62 D.4 How detailed should a FRA be? ........................................................................................... 64 AECOM Jersey Strategic Flood Risk Assessment AECOM Project Number: 60627145 Figures Figure 3-1 Summary of coastal flooding mechanisms ......................................................................................... 6 Figure 3-2 Source Pathway Receptor Model ...................................................................................................... 7 Figure 4-1 Grands Vaux catchment area24 ....................................................................................................... 25 Figure 5-1 Pumping station locations ............................................................................................................... 31 Figure 5-2 Jersey Water Supply Schematic (Jersey Water, 2019) ..................................................................... 33 Figure 5-3 Coastal Management Unit locations, Jersey Shoreline Management Plan ........................................ 35 Figure 6-1 Online and Offline Flood Storage Areas........................................................................................... 38 Tables Table 2-1 Strategic Spatial Options considered for the Island Plan (2021-2030) .................................................. 4 Table 3-1 Expressing the probability of flooding .................................................................................................. 7 Table 4-1 Areas of development modelled to be at high risk of flooding from the tide (present day, not including the presence of defences) ............................................................................................................................... 12 Table 4-2 Areas modelled to be at risk of flooding from the tide as a result of climate change ............................ 13 Table 4-3 Records of