Oxford City Council Strategic Flood Risk Assessment for Oxford City Final Report March 2011
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Oxford City Council Strategic Flood Risk Assessment for Oxford City Final Report March 2011 The Planning Policy Team Oxford City Council Ramsay House 10 St. Ebbes Street Oxford OX1 1PT Strategic Flood Risk Assessment for Oxford City - Update March 2011 Final Report Oxford City Council This page left intentionally blank 5093353_DG_062_002_F2.docx Strategic Flood Risk Assessment for Oxford City - Update March 2011 Final Report Oxford City Council Notice This document has been produced by ATKINS for Oxford City Council solely for the purpose of describing the Oxford City Strategic Flood Risk Assessment. It may not be used by any person for any other purpose other than that specified without the express written permission of ATKINS. Any liability arising out of use by a third party of this document for purposes not wholly connected with the above shall be the responsibility of that party who shall indemnify ATKINS against all claims costs damages and losses arising out of such use. Document History JOB NUMBER: 5093353 DOCUMENT REF: 5093353/62/DG/003 March F2 Final Report A Fenna S Fox E Ainsworth M Jackson 2010 F1 Final Report N Maynard S Fox E Ainsworth M Jackson Nov 2010 D1 Draft Report N Maynard S Fox E Ainsworth M Jackson Oct 2010 Purpose and Revision Originated Checked Reviewed Authorised Date Description 5093353_DG_062_002_F2.docx Page 1 Strategic Flood Risk Assessment for Oxford City - Update March 2011 Final Report Oxford City Council This page left intentionally blank 5093353_DG_062_002_F2.docx Page 2 Strategic Flood Risk Assessment for Oxford City - Update March 2011 Final Report Oxford City Council Preface This Strategic Flood Risk Assessment (SFRA) has been produced in March 2011 to present the current understanding of flood risk within the City of Oxford. SFRAs are living documents and should therefore be reviewed and updated on a regular basis, this SFRA is the latest update of a document which was first published in July 2008. Since the preceding publication, a number of refined and new flood risk data has become available and this document has incorporated these to present a current, and robust, flood risk evidence base. The newly available data includes: • The most recently published Environment Agency Flood Map • Refined flood risk mapping for Boundary Brook • The Environment Agency indicative surface water map • The most recent record of sewer flooding incidents from Thames Water In addition to these datasets, further guidance and comment has been included for the following: • Additional information regarding groundwater flooding and site specific guidance for managing risks associated with groundwater has been included. • Enhanced guidance on the use of Sustainable Urban Drainage Systems which provides more detailed and specific information relevant to the sensitive nature of Oxford. • The document has identified potential dry island sites within Oxford and has provided guidance on how to manage the associated access issues when progressing dry islands sites for development. A reference has been added to state that FRAs may be required for sites which are not affected by fluvial flooding. • Further narration provided for historic flood events. • The SFRA makes reference to the Pitt report and the City Council’s ability to respond to flood risk within the city. 5093353_DG_062_002_F2.docx Page 3 Strategic Flood Risk Assessment for Oxford City - Update March 2011 Final Report Oxford City Council This page left intentionally blank 5093353_DG_062_002_F2.docx Page 4 Strategic Flood Risk Assessment for Oxford City - Update March 2011 Final Report Oxford City Council Table of Contents 1.0 Introduction ................................................................................................................. 7 1.1 Need for a Flood Risk Assessment ................................................................. 7 1.2 Objectives ........................................................................................................ 7 1.3 Scope of this Document .................................................................................. 8 1.4 Flood Risk in Oxford ........................................................................................ 8 1.5 Local Planning Policy Relating to Flood Risk .................................................. 9 2.0 Phase 1 – Desk Research ........................................................................................ 11 2.1 Summary ....................................................................................................... 11 2.2 Flooding Sources ........................................................................................... 11 2.3 Recent Studies on Flood Risk ....................................................................... 17 2.4 Historic Flood Events ..................................................................................... 19 2.5 Existing Flood Defences ................................................................................ 21 2.6 Flood Warning ............................................................................................... 23 2.7 Potential Development Sites and Flood Warning .......................................... 24 2.8 Emergency Plans .......................................................................................... 24 3.0 Phase 2 – Analysis ................................................................................................... 26 3.1 Flood Risk Sensitivities .................................................................................. 26 4.0 PPS25 and the Sequential Test ............................................................................... 28 4.1 Background.................................................................................................... 28 4.2 Sequential Test .............................................................................................. 28 4.3 Flood Zone Definition .................................................................................... 29 4.4 Updating the Flood Maps for this SFRA ........................................................ 31 4.5 Assessing Flood Risk Using the Sequential Approach ................................. 32 5.0 Flood Risk in Oxford City ........................................................................................ 33 5.1 Introduction .................................................................................................... 33 5.2 Summary of Results for Oxford City .............................................................. 33 5.3 Summary of Results for the West End Area .................................................. 35 6.0 Flood Management through Oxford city ................................................................ 41 6.1 Overview ........................................................................................................ 41 6.2 Strategic Flood Risk Management ................................................................ 41 6.3 River Corridor Management .......................................................................... 42 6.4 Surface Water Management .......................................................................... 43 6.5 Sustainable Urban Drainage Systems .......................................................... 44 6.6 Groundwater Flood Guidance ....................................................................... 45 6.7 Emergency Evacuation Routes ..................................................................... 46 6.8 Dry Islands ..................................................................................................... 47 7.0 Conclusions and Recommendations ..................................................................... 49 7.1 Conclusions ................................................................................................... 49 7.2 Recommendations ......................................................................................... 50 8.0 References ................................................................................................................ 52 Tables Table 1: Thames Water Figures on Flooding from Sewers ..................................................... 12 Table 2: The Groundwater Register (Source. The Environment Agency) ............................... 15 Table 3: Historic Flood Events in Oxford ................................................................................. 19 Table 4: Narration of Historic Events in Oxford ....................................................................... 21 Table 5: Potential Development Sites Within Flood Warning Areas ....................................... 24 Table 6: Flood Risk Vulnerability and Flood Zone ‘Compatibility’ ........................................... 31 Table 7: Return Period of data used to delineate the PPS25 Flood Zones ............................ 32 Table 8: Summary of the flood risk status of proposed sites .................................................. 36 Table 9: Summary of appropriate development type for proposed sites ................................. 37 Table 10: Sites Requiring FRAs .............................................................................................. 38 Table 11: Susceptibility to Surface Water Flooding ................................................................. 39 Table 12: Impact of Climate Change on Flood Zone 2 Sites................................................... 40 5093353_DG_062_002_F2.docx Page 5 Strategic Flood Risk Assessment