February 2010 DURHAM COUNTY (LEVEL 1) Strategic Flood Risk Assessment (SFRA) – Level 1 Report Number: P9514100112-A02 Distribution: Durham County Council Environment Agency Northumbrian Water Durham County SFRA (Level 1) Table of Contents 1.0 INTRODUCTION ........................................................................................................................................................1 2.0 BACKGROUND TO THE SFRA ................................................................................................................................1 3.0 THE POLICY FRAMEWORK .....................................................................................................................................2 4.0 DATA INFORMING THE SFRA ................................................................................................................................. 4 4.1 Historical Flooding .........................................................................................................................................4 4.2 Areas at Risk of Flooding from Rivers and the Sea.......................................................................................5 4.2.1 Flood Zone Maps ....................................................................................................................................5 4.2.2 Flood Defences .......................................................................................................................................6 4.2.3 Flood Warning Areas ...............................................................................................................................6 4.3 Topography ...................................................................................................................................................6 4.4 Geology .........................................................................................................................................................6 4.5 Previous Flooding Related Investigations .....................................................................................................7 5.0 THE RISK OF FLOODING IN DURHAM COUNTY ...................................................................................................8 5.1 Brief Description of Durham County ..............................................................................................................8 5.2 History of Flooding in Durham County ..........................................................................................................8 5.3 Risk of Flooding from Rivers .........................................................................................................................9 5.4 Risk of Flooding from the Sea .......................................................................................................................9 5.5 Risk of Flooding from Surface Water ............................................................................................................9 5.6 Risk of Flooding from Groundwater .............................................................................................................10 5.7 Risk of Flooding from Reservoirs ................................................................................................................10 5.8 Risk to Life due to Flooding (Flood Hazard) ................................................................................................11 5.9 Climate Change ..........................................................................................................................................12 5.9.1 Impact of Climate Change upon Fluvial (River) Flooding ......................................................................14 5.9.2 Impact of Climate Change upon Tidal Flooding .....................................................................................14 5.9.3 Impact of Climate Change upon Surface Water Flooding ......................................................................14 6.0 PLANNING FOR FLOOD RISK IN DURHAM COUNTY ..........................................................................................16 6.1 Responsibility for Flood Risk Management ................................................................................................. 16 6.2 Spatial Planning ..........................................................................................................................................17 6.2.1 PPS25 Flood Zones ..............................................................................................................................17 6.2.2 The Sequential Test ..............................................................................................................................19 February 2010 Report No. P9514100112-A02 i Durham County SFRA (Level 1) 6.2.3 The Exception Test................................................................................................................................20 6.3 Development management .........................................................................................................................21 6.3.1 Adopting a Sequential Approach ...........................................................................................................21 6.3.2 Applying the Exception Test ..................................................................................................................22 6.3.3 Flood Risk Assessment .........................................................................................................................22 6.3.4 Mitigating the Risk of Flooding through Design .....................................................................................22 6.4 Emergency Planning ...................................................................................................................................24 7.0 MITIGATING THE RISK OF FLOODING THROUGH DEVELOPMENT ..................................................................25 7.1 The Flood Risk Assessment (FRA) .............................................................................................................25 7.2 Data Sources for Developers ......................................................................................................................27 7.3 Site Selection & Site Layout (A Sequential Approach) ................................................................................27 7.4 Building Design ...........................................................................................................................................28 7.5 Sustainable Drainage Systems (SUDS) ......................................................................................................30 7.5.1 Overview ...............................................................................................................................................30 7.5.2 SUDS Maintenance ...............................................................................................................................31 7.5.3 SUDS Approaches ................................................................................................................................32 7.5.4 The Application of SUDS in County Durham .........................................................................................33 7.6 Safe Site Access .........................................................................................................................................34 7.7 Flood Warning, Planning and Preparation ..................................................................................................35 7.7.1 Flood Warning .......................................................................................................................................35 7.7.2 Evacuation Plan (Developers & Site Operators) ....................................................................................35 7.7.3 Flood Plan (Residents & Businesses) ...................................................................................................35 8.0 CONCLUSIONS .......................................................................................................................................................36 9.0 A LIVING DOCUMENT ............................................................................................................................................36 February 2010 Report No. P9514100112-A02 ii Durham County SFRA (Level 1) FIGURES Figure 1 Locality Plan Figure 2 Policy Framework (Flood Risk Management) Figure 3 Hierarchy of Flood Risk Management Figure 4 Flood Warning Areas Figure 5 Topography Figure 6 Geology Figure 7 Flood Defences & Flood Hazard Figure 8 Reservoirs Figure 9 Permissible Land Uses Figure 10 Levels of Detail for a Site Based Flood Risk Assessment (FRA) Figure 11 Recommended Building Design Approach (vs Flood Depth) Figure 12 Hierarchy of SUDS Techniques Figure 13 DG5 Register Summary (Northumbrian Water) APPENDICES Appendix A Historical Flooding Incidents Appendix B SFRA Flood Maps (PPS25) Appendix C The Policy Framework Appendix D Previous Investigations Appendix E Data Received to Inform Durham County SFRA Appendix F Flood Risk Vulnerability Classification (Land Uses) Appendix G Methodology for delineating Zone 3b Functional Floodplain Appendix H The ‘Simple’ Method (FD2320) – Flood Defence Failure Appendix I Sustainable Drainage Systems (SUDS) - A Guide for Developers Appendix J Impact of Climate Change (Zone 3a