Flood Risk Scoping Assessment
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Appendix G FLOOD RISK SCOPING ASSESSMENT New Thames Crossing east of Reading Flood Risk Scoping Assessment On behalf of: Wokingham Borough Council Project Ref: 37006/4001 | Rev: - | Date: October 2016 Office Address: Caversham Bridge House, Waterman Place, Reading, Berkshire RG1 8DN T: +44 (0)118 950 0761 F: +44 (0)118 959 7498 E: [email protected] Flood Risk Scoping Assessment New Thames Crossing east of Reading Document Control Sheet Project Name: New Thames Crossing east of Reading Project Ref: 37006/4001 Report Title: Flood Risk Scoping Assessment Doc Ref: - Date: October 2016 Name Position Signature Date Prepared by: Jodie Hall Assistant Modeller J. Hall Reviewed by: Richard Fisher Associate R.Fisher Approved by: Chris Downs Director of Water D.Walker For and on behalf of Peter Brett Associates LLP Revision Date Description Prepared Reviewed Approved Peter Brett Associates LLP disclaims any responsibility to the Client and others in respect of any matters outside the scope of this report. This report has been prepared with reasonable skill, care and diligence within the terms of the Contract with the Client and generally in accordance with the appropriate ACE Agreement and taking account of the manpower, resources, investigations and testing devoted to it by agreement with the Client. This report is confidential to the Client and Peter Brett Associates LLP accepts no responsibility of whatsoever nature to third parties to whom this report or any part thereof is made known. Any such party relies upon the report at their own risk. © Peter Brett Associates LLP 2016 \\pba.int\cbh\Projects\37006 3rd Thames ii Crossing\Env\37006 New Thames Crossing_Oct Draft for Issue\4. Additional documents\4. Water Environment \37006_NTC_Scoping_FRA_Oct16_Final.docx Flood Risk Scoping Assessment New Thames Crossing east of Reading Contents 1 Introduction ................................................................................................................................. 2 Scope of Report ............................................................................................................. 2 Sources of Information .................................................................................................. 2 Policy Context ................................................................................................................ 3 2 Proposed Route Setting ............................................................................................................. 4 Proposed Route Description ......................................................................................... 4 Proposed Development ................................................................................................. 5 Topography ................................................................................................................... 5 Watercourses and Flood Defences ............................................................................... 5 Geology ......................................................................................................................... 6 3 Overview of Flood Risk .............................................................................................................. 7 EA Flood Maps .............................................................................................................. 7 Wokingham Borough Council Preliminary Flood Risk Assessment .............................. 9 Oxfordshire County Council Preliminary Flood Risk Assessment .............................. 10 Wokingham Borough Council Strategic Flood Risk Assessment ................................ 10 South Oxfordshire District Council Strategic Flood Risk Assessment ........................ 11 EA Product 4 Flood Data ............................................................................................. 12 Impact of Climate Change ........................................................................................... 14 4 NPPF Sequential Test and Vulnerability ................................................................................. 16 5 Flood Risk Implications for Development .............................................................................. 17 Introduction .................................................................................................................. 17 Bridge Soffit Levels...................................................................................................... 17 Conservation of Flood Storage and Flow Routes ....................................................... 17 Surface Water and SuDS ............................................................................................ 18 6 Conclusions ............................................................................................................................... 19 \\pba.int\cbh\Projects\37006 3rd Thames iii Crossing\Env\37006 New Thames Crossing_Oct Draft for Issue\4. Additional documents\4. Water Environment \37006_NTC_Scoping_FRA_Oct16_Final.docx Flood Risk Scoping Assessment New Thames Crossing east of Reading Tables Table 3.1: EA Modelled Flood Data ..................................................................................................... 14 Table 3.2: Climate Change – Peak River Flow Allowances ................................................................. 15 Figures Figure 2.1: Proposed Route Location Plan ............................................................................................ 4 Figure 2.2: View east along River Thames from Wokingham Canoe Club (showing right bank floodplain) 5 Figure 3.1: EA Flood Zone Map ............................................................................................................. 7 Figure 3.2: EA Flood Risk from Reservoirs Map .................................................................................... 8 Figure 3.3: EA Surface Water Flood Risk Map ...................................................................................... 9 Figure 3.4: Extract of WBC PFRA Map 6.2 – Areas Susceptible to Groundwater Flooding ................. 10 Figure 3.5: WBC SFRA Map 7-5 Character Areas Map 5 of 17 ........................................................... 11 Figure 3.6: Extract of SODC SFRA Figure 2.1 ..................................................................................... 12 Figure 3.7: EA Product 4 Historical Data .............................................................................................. 13 Figure 3.8: EA Product 4 Modelled Flood Extents ............................................................................... 13 Table 3.1: EA Modelled Flood Data ..................................................................................................... 14 Appendices Annex A Proposed Route Information Annex B EA Flood Data Annex C WBC, SODC and OCC information \\pba.int\cbh\Projects\37006 3rd Thames iv Crossing\Env\37006 New Thames Crossing_Oct Draft for Issue\4. Additional documents\4. Water Environment \37006_NTC_Scoping_FRA_Oct16_Final.docx Flood Risk Scoping Assessment New Thames Crossing east of Reading Executive Summary This Flood Risk Scoping Assessment has been prepared by Peter Brett Associates LLP, on behalf of our client, Wokingham Borough Council (WBC), to consider the flood risk implications for the proposed ‘New Thames Crossing east of Reading’, a proposed road bridge over the River Thames and Caversham Lakes to the east of Reading. The assessment will provide input for a Strategic Outline Business Case (SOBC) for the bridge. For the purpose of the study, the proposed study area is the Thames floodplain corridor within the vicinity of the proposed bridge crossing, from Caversham Lock upstream to Sonning Lock downstream. The Environment Agency (EA) Flood Zone map shows the proposed route lies within Flood Zone 3 of the River Thames, defined as: Flood Zone 3 ‘High Probability’ (greater than 1 in 100 (1%) annual probability of river flooding) The proposed development consists of ‘Essential Infrastructure’ development which is considered appropriate within Flood Zone 3 subject to the Exception Test (ref: (reference National Planning Policy Framework (NPPF) Planning Practice Guidance Table 3). In considering the feasibility of the proposed development, the following key aspects have been addressed: - Vulnerability to flooding from all sources; No increased flood risk to third parties as a result of the development. Flood risk will need to be appropriately mitigated through measures including: Proposed bridge soffit levels are set a minimum of 600mm above the modelled 1 in 100 (1%) annual probability plus allowance for climate change level, in accordance with the requirements of Wokingham Borough Council, South Oxfordshire District Council and the EA ‘Flood Risk Assessments: Climate Change Allowances’ guidance; Effective bridge design to minimise impacts on floodplain storage and flood flow routes (with the provision of flood compensation measures and potentially flood defence measures); Appropriate management of surface water. \\pba.int\cbh\Projects\37006 3rd Thames Crossing\Env\37006 New Page: 1 Thames Crossing_Oct Draft for Issue\4. Additional documents\4. Water Environment\37006_NTC_Scoping_FRA_Oct16_Final.docx Flood Risk Scoping Assessment New Thames Crossing east of Reading 1 Introduction Scope of Report 1.1.1 This Flood Risk Scoping Assessment has been prepared by Peter Brett Associates LLP, on behalf of our client, Wokingham Borough Council