Strategic Flood Risk Assessment (SFRA)
Total Page:16
File Type:pdf, Size:1020Kb
1.1.1.1 LP/Ev/9f Bracknell Forest Borough Council Level 2 SFRA Final Report September 2019 Bracknell Forest Council Time Square Market Street BRACKNELL Berkshire RG12 1JD JBA Project Manager Anna Beasley 8a Castle Street WALLINGFORD Oxfordshire OX10 8DL Revision History Revision Ref / Date Issued Amendments Issued to Draft v1.0 / 11 Jan 2018 Marie O'Sullivan, Julia Greene Draft Final v2.0 / 13 June Comments from Bracknell Marie O'Sullivan, Julia 2018 Forest Council Greene Final v3.0 / 11 January 2019 Comments from Bracknell Natalie Hird, Julia Greene Forest Council and inclusion of additional sites Final v4.0 / 16 July 2019 Comments from Bracknell Natalie Hird, Julia Greene Forest Council, inclusion and removal of sites. Final v5.0 / 05 September Comments from Bracknell Natalie Hird, Julia Greene 2019 Forest Council Contract This report describes work commissioned by Bracknell Forest Council by an email dated 3 October 2017. Bracknell Forest Council's Representative for the contract was Marie O'Sullivan. Anna Beasley, Paul Eccleston, Anna Hastings and Cheryl Briars of JBA Consulting carried out this work. Prepared by .................................................. Cheryl Briars BSc MSc Assistant Analyst ....................................................................... Anna Beasley BSc MSc CEnv MCIWEM C.WEM Technical Director Reviewed by ................................................. Paul Eccleston BA CertWEM CEnv MCIWEM C.WEM Technical Director Purpose This document has been prepared as a Final Report for Bracknell Forest Council. JBA Consulting accepts no responsibility or liability for any use that is made of this document other than by the Client for the purposes for which it was originally commissioned and prepared. JBA Consulting has no liability regarding the use of this report except to Bracknell Forest Council. 2016s5363 - Bracknell Forest Council - SFRA L2 Final Report v5.0 (Sep 2019) i Acknowledgements With thanks to Marie O'Sullivan and Julia Greene (Bracknell Forest Council), Clark Gordon (Environment Agency), and Thames Water. Copyright © Jeremy Benn Associates Limited 2019 Carbon Footprint A printed copy of the main text in this document will result in a carbon footprint of 82g if 100% post- consumer recycled paper is used and 105g 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 to reduce its per capita carbon emissions. 2016s5363 - Bracknell Forest Council - SFRA L2 Final Report v5.0 (Sep 2019) ii Executive Summary Bracknell Forest Council is undertaking the preparation of a new Bracknell Forest Local Plan (BFLP). As part of this process it is preparing an evidence base which will support the policies and allocations included in the document. This Level 2 Strategic Flood Risk Assessment (SFRA) is one piece of the evidence base, which will help to inform policy development and the selection of site allocations for inclusion within the BFLP. On the basis of the Level 1 SFRA and the Sustainability Appraisal (SA), the Council identified that all the necessary development required over the plan period cannot be accommodated by sites identified as being at low flood risk from all sources (noting that the SA process discounted some low risk sites on other planning grounds), and additional sites would be required to enable delivery of the level of development set out in the BFLP. The Council therefore progressed to a Level 2 SFRA for 28 sites and 3 Clusters to provide further detail and development solutions for prescribed sites and for the application of the Sequential and Exception Test (if required). The Level 2 SFRA draws upon all the information and data sources that were compiled as part of the Level 1 assessment, examining them in more detail on a site-by-site basis for the 20 sites and 4 Clusters. It also examines detailed hydraulic modelling outputs, such as depth, hazard and velocity, for floodplain areas. The impacts of climate change on different sources of flooding has been modelled or investigated in more detail. The cumulative impact of development has been considered. The presence of flood defences and residual risk, and the risk of structure blockage has also been assessed. The flood risk summary sheets and GeoPDF maps in Appendix A give flood risk information for each Level 2 site to support the application of the Sequential Test and inform the Council whether the Exception Test would be required. These summary sheets and maps form the main output of the Level 2 SFRA. If the Council finds them to pass the Sequential Test (and Exception test if appropriate), site-specific detailed flood risk assessments will be required on all of these sites to ensure that they are designed safely. The Level 1 and 2 SFRA has provided thorough recommendations on site specific requirements to be addressed by FRAs, guidance for site design and making development safe from flooding, and requirements for SuDS and surface water management. It is important to recognise that the SFRA has been developed using the best available information at the time of preparation. This relates both to the current risk of flooding from rivers, and the potential impacts of future climate change. In particular, the Environment Agency have indicated that at the time of publication they have commenced re-modelling of The Cut. Developers must ensure that they obtain and use the most up to date model data for detailed site-specific flood risk assessments. 2016s5363 - Bracknell Forest Council - SFRA L2 Final Report v5.0 (Sep 2019) iii Executive Summary ............................................................................................................ iii 2 Introduction ............................................................................................................ 1 2.1 Introduction ........................................................................................................................ 1 2.2 SFRA objectives ................................................................................................................. 1 2.3 How to use the Level 2 SFRA ............................................................................................ 1 2.4 Stakeholder engagement ................................................................................................... 1 3 How were sites identified for a Level 2 assessment? ............................................ 2 4 What flood risk information has been used? ......................................................... 3 4.1 Data sources ...................................................................................................................... 3 4.2 Environment Agency detailed hydraulic models ................................................................. 3 5 How has climate change been assessed? ............................................................ 3 5.2 Fluvial flooding ................................................................................................................... 4 5.3 Surface water flooding ....................................................................................................... 4 5.4 Groundwater flooding ......................................................................................................... 4 6 How has residual risk been assessed? ................................................................. 5 6.2 Flood defence failure and overtopping ............................................................................... 5 6.3 Structure blockage ............................................................................................................. 5 7 How has cumulative impact of development been assessed? .............................. 5 8 How to interpret groundwater flood risk data ......................................................... 7 8.2 Interpreting the mapping .................................................................................................... 7 8.3 Consequences for spatial planning .................................................................................... 7 9 Level 2 site flood risk summaries .......................................................................... 8 9.2 Summary sheets ................................................................................................................ 8 9.3 Site maps ........................................................................................................................... 9 10 Future use of SFRA data ....................................................................................... 12 Appendices ......................................................................................................................... I A Level 2 site flood risk summary sheets and maps ................................................. I 2016s5363 - Bracknell Forest Council - SFRA L2 Final Report v5.0 (Sep 2019) List of Tables Table 2-1: Level 2 SFRA engagement ............................................................................... 2 Table 4-1: Environment Agency detailed hydraulic models within Bracknell Forest at the time of publication ............................................................................................. 3 Table 5-1: Climate change allowances ............................................................................... 4 Table 7-1: Potential for cumulative impact within a catchment .......................................... 7 Table 9-1: Site map explanatory