Gloucester, Cheltenham & Tewkesbury Joint Core Strategy
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Gloucester, Cheltenham & Tewkesbury Joint Core Strategy Strategic Flood Risk Assessment for Local Development Framework Level 2 FINAL REPORT October 2011 Halcrow Group Limited Guidance on the Use of SFRA Documentation: This Level 2 SFRA report and accompanying documents are part of a suite of documents designed to provide further information of flood risk within the Joint Core Strategy (JCS) area: • SFRA Level 1 (Published September 2008) provides an initial assessment of fluvial flood risk across the whole JCS area. • SFRA Level 2 (Published October 2011) provides a detailed assessment of multiple flood sources for specific sites within the JCS area which at the time of commissioning were potential development sites. • Additional work is currently being undertaken to identify whether additional sites need to be assessed as a supplement to SFRA L2. • Further updates to the existing documents may be undertaken when deemed necessary and expedient. • Surface Water Management Plans (SWMPs) are in progress for Gloucester, Cheltenham, Tewkesbury and Bishops Cleeve. The findings of these studies (and any additional SWMPS undertaken in the area) will be taken into consideration when completed and any necessary changes will be fed back into the SFRA Level 2. • New Flood Zone information contained herein should be used in conjunction with the Environment Agency’s existing Flood Zone mapping. Strategic Flood Risk Assessment Gloucester, Cheltenham & Tewkesbury JCS Gloucester, Cheltenham & Tewkesbury Joint Core Strategy Strategic Flood Risk Assessment for Local Development Framework Level 2 – FINAL Volume 1 Contents Amendment Record This report has been issued and amended as follows: Issue Revision Description Date Signed 1 0 Draft Report 09/10 RD 2 0 Final Draft Report incorporating 02/11 RD changes following LA & EA comments and the River Chelt assessment 2 1 Final Report 09/11 JRP 3 0 Final Report 10/11 JRP Prepared by: Caroline Mills, Michael Grogan, Michael Green, Stephen Bilby, Habton Gebre Reviewed by: John Parkin and the Environment Agency Approved by: Phil Marsh Strategic Flood Risk Assessment Gloucester, Cheltenham & Tewkesbury JCS This page is left intentionally blank Strategic Flood Risk Assessment Gloucester, Cheltenham & Tewkesbury JCS Contents Contents..................................................................................................................................................i List of Tables & Figures ....................................................................................................................... v Preface .................................................................................................................................................vii 1 Introduction...................................................................................................................................1 1.1 Project Overview ........................................................................................................................1 1.2 Background to Strategic Flood Risk Assessment......................................................................2 1.3 Aims & Objectives ......................................................................................................................4 1.4 Background to the study area ....................................................................................................6 2 Planning Context..........................................................................................................................7 2.1 Local Planning Context ..............................................................................................................7 2.2 Relevant External Policy: Catchment Flood Management Plans & Shoreline Management Plans… ................................................................................................................................................7 2.3 Surface Water Management Plans ..........................................................................................11 3 Level 2 SFRA Method.................................................................................................................13 3.1 Introduction ..............................................................................................................................13 3.2 Level 2 SFRA Site Assessment Assessment Method .............................................................14 Flood Risk Suitability Assessment Criteria...............................................................................15 4 Hydraulic & Hydrological Approach.........................................................................................17 4.2 Hydrological Approach.............................................................................................................17 4.3 Hydraulic Approach..................................................................................................................17 4.4 UK Flood Hazard......................................................................................................................17 4.5 Breach and Overtopping Scenarios .........................................................................................19 Defence Breach and Overtopping ............................................................................................19 Canal Breach and Overtopping ................................................................................................19 4.6 Model QA .................................................................................................................................19 5 Gloucester City Results.............................................................................................................21 5.1 Overview ..................................................................................................................................21 5.2 Aim of Level 2 SFRA in Gloucester .........................................................................................23 5.3 Historic Flood Risk ...................................................................................................................24 5.4 Assessment of Flood Risk........................................................................................................26 5.5 Residual Risk ...........................................................................................................................33 i Strategic Flood Risk Assessment Gloucester, Cheltenham & Tewkesbury JCS 5.6 Conclusion ...............................................................................................................................34 6 River Chelt at Cheltenham Results...........................................................................................35 6.1 Overview ..................................................................................................................................35 6.2 Aim of Level 2 SFRA in Cheltenham .......................................................................................35 6.3 Historic Flooding ......................................................................................................................36 6.4 Assessment of Flood Risk........................................................................................................37 6.5 Residual Risk ...........................................................................................................................39 6.6 Conclusion ...............................................................................................................................39 7 Hatherley Brook & Ham Brook at Leckhampton & Shurdington Results.............................41 7.1 Overview ..................................................................................................................................41 7.2 Aim of Level 2 SFRA in Leckhampton & Shurdington .............................................................42 7.3 Historic Flooding ......................................................................................................................43 7.4 Assessment of Flood Risk........................................................................................................44 7.5 Residual Risk ...........................................................................................................................47 7.6 Conclusion ...............................................................................................................................47 8 River Swilgate, Hyde Brook & Leigh Brook at Swindon Results ..........................................49 8.1 Overview ..................................................................................................................................49 8.2 Aim of Level 2 SFRA Assessment at Swindon ........................................................................50 8.3 Historic Flooding ......................................................................................................................51 8.4 Assessment of Flood Risk........................................................................................................52 8.5 Residual Risk ...........................................................................................................................54 8.6 Conclusion ...............................................................................................................................55 9 Horsebere Brook at Brockworth Results.................................................................................57