Gloucester City Council Strategic Flood Risk Assessment for Local Development Framework Level 1 Volume 1 - FINAL September 2008 Halcrow Group Limited Strategic Flood Risk Assessment Gloucester City Council Strategic Flood Risk Assessment Gloucester City Council Gloucester City Council Strategic Flood Risk Assessment for Local Development Framework Level 1 – FINAL Volume 1 Contents Amendment Record This report has been issued and amended as follows: Issue Revision Description Date Signed 1 Draft Report 25/04/08 RD 2 Final Report 22/08/09 RD 2 A Final Report 23/09/08 RD Prepared by: Caroline Mills & Beccy Dunn Checked by: Beccy Dunn & Environment Agency (West Area, Midlands Region) Approved by: Shirel Saranga & Environment Agency (West Area, Midlands Region) Strategic Flood Risk Assessment Gloucester City Council This page is left intentionally blank 1 Strategic Flood Risk Assessment Gloucester City Council Contents Contents.................................................................................................................................................2 List of Tables & Figures .......................................................................................................................6 Executive Summary ..............................................................................................................................8 1 Introduction.................................................................................................................................10 1.1 Terms of Reference .................................................................................................................10 1.2 Project Aims .............................................................................................................................10 1.3 Project Objectives ....................................................................................................................10 1.4 Project Deliverables .................................................................................................................11 1.5 Outcomes of the SFRA Process ..............................................................................................11 1.6 SFRA Context ..........................................................................................................................14 1.7 The Study Area ........................................................................................................................15 1.8 Main Rivers, Hydrology, Geology and Topography.................................................................16 1.9 Key Recommendations: Chapter One .....................................................................................22 2 Study Methodology ....................................................................................................................24 2.1 Level 1 SFRA Methodology .....................................................................................................24 2.2 Need for a Level 2 SFRA .........................................................................................................25 2.3 Technical Background..............................................................................................................25 2.4 Environment Agency Flood Zone Maps...................................................................................26 2.5 Key Recommendations: Chapter Two .....................................................................................27 3 Planning Context........................................................................................................................28 3.1 Introduction ..............................................................................................................................28 3.2 Planning Policy Framework .....................................................................................................28 3.3 National Planning Policy ..........................................................................................................28 3.4 Regional Planning Policy .........................................................................................................30 3.5 Local Planning Policy...............................................................................................................34 3.6 Key Recommendations: Chapter Three...................................................................................36 4 Data Collection and Review ......................................................................................................38 4.1 Overview of Flooding Sources .................................................................................................38 4.2 Approach to Data Gathering ....................................................................................................38 4.3 The Pitt Review ........................................................................................................................38 4.4 Findings of the Regional Flood Risk Appraisal ........................................................................39 4.5 Historical Flooding....................................................................................................................40 4.6 Fluvial Flood Risk in Gloucester City Council ..........................................................................46 2 Strategic Flood Risk Assessment Gloucester City Council 4.7 Tidal Flood Risk in Gloucester City..........................................................................................48 4.8 Issues With Existing Flood Maps .............................................................................................49 4.9 Flooding from Other Sources...................................................................................................50 4.10 Flooding from Artificial Drainage Systems (Sewers) ...........................................................50 4.11 Flooding from Surface Water...............................................................................................52 4.12 Flooding from Impounded Water Bodies .............................................................................54 4.13 Flooding from Groundwater.................................................................................................56 4.14 Key Recommendations: Chapter Four ................................................................................58 5 Strategic Flood Risk Mapping...................................................................................................60 5.1 Strategic Flood Risk Maps .......................................................................................................60 5.2 Hydraulic (River) Models..........................................................................................................60 5.3 Sewer Flooding ........................................................................................................................64 5.4 Flooding from Surface Water, Impounded Water Bodies and Groundwater ...........................64 5.5 Climate Change .......................................................................................................................64 5.6 Key Recommendations: Chapter Five .....................................................................................69 6 Flood Warning Systems and Flood Risk Management Measures.........................................70 6.1 Flood Risk Management ..........................................................................................................70 6.2 Catchment Flood Management Plans......................................................................................70 6.3 Shoreline Management Plans..................................................................................................71 6.4 Flood Risk Management Strategies.........................................................................................72 6.5 Summary of Environment Agency Policies and Options .........................................................73 6.6 Flood Defences........................................................................................................................74 6.7 Culverts ....................................................................................................................................78 6.8 Storage Areas ..........................................................................................................................80 6.9 Residual Risk ...........................................................................................................................81 6.10 Existing Flood Warning System...........................................................................................82 6.11 Flood Response Plan ..........................................................................................................84 6.12 Key Recommendations: Chapter Six...................................................................................89 7 Flood Risk Management Policy Considerations .....................................................................90 7.1 Overview ..................................................................................................................................90 7.2 Policy Considerations...............................................................................................................90 7.3 Development Control Policies..................................................................................................92