Gas-to-Grid Anaerobic Digestion Plant Tongue End, Deeping St. Nicholas Flood Risk Assessment and Surface Water Drainage Strategy SLR Ref: 408.03643.00033 April 2016 Version: 2 rsion JH Walter LLP i SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016 CONTENTS 1.0 INTRODUCTION ............................................................................................................ 1 1.1 Context ................................................................................................................ 1 1.2 Site Location and Features................................................................................ 1 1.3 Topography ......................................................................................................... 2 1.4 Hydrology and Surface Water Drainage ........................................................... 3 1.5 Geological and Hydrogeological Features ....................................................... 6 1.6 Development Proposals..................................................................................... 6 1.7 Flood Zone Classification (Environment Agency) .......................................... 7 1.8 Flood Zone Classification (Strategic Flood Risk Assessment) ..................... 9 1.9 Flood Zone Classification Requirements ....................................................... 10 1.10 Flood Risk Vulnerability................................................................................... 10 1.11 Flood Risk Compatibility ................................................................................. 10 1.12 Sequential Test ................................................................................................. 10 1.13 Exception Test .................................................................................................. 12 2.0 SOURCES OF INFORMATION ................................................................................... 13 2.1 Topographical Survey ...................................................................................... 13 2.2 Internal Drainage Board Watercourse Map .................................................... 13 2.3 Site Plans .......................................................................................................... 13 2.4 EA Mapping ....................................................................................................... 13 2.5 Strategic Flood Risk Assessment ................................................................... 13 2.6 Preliminary Flood Risk Assessment .............................................................. 13 2.7 Joint Lincolnshire Flood Risk and Drainage Management Strategy ........... 14 2.8 Historic Flooding .............................................................................................. 14 3.0 FLOOD RISK ASSESSMENT ..................................................................................... 15 3.1 Methodology & Best Practice .......................................................................... 15 3.2 National and Local Planning Policy ................................................................ 15 3.3 Screening Study ............................................................................................... 15 4.0 TECHNICAL ASSESSMENT OF FLOOD RISK ......................................................... 16 4.1 Historic Flooding .............................................................................................. 16 4.2 Flooding from Tidal and Fluvial Sources ....................................................... 16 4.3 Flooding from Surface Water .......................................................................... 17 4.4 Flooding from Overland Flow .......................................................................... 21 4.5 Flooding from Groundwater ............................................................................ 21 4.6 Flooding from Sewers & Water Mains ............................................................ 21 4.7 Flooding from Reservoirs and Canals ............................................................ 22 4.8 Flooding from Infrastructure Failure .............................................................. 23 4.9 Potential Flood Risk to Off-Site Areas ............................................................ 23 5.0 CLIMATE CHANGE ..................................................................................................... 24 5.1 Anticipated Lifetime of Development ............................................................. 24 5.2 Climate Change Allowances ........................................................................... 24 5.3 Impacts on Flood Risk ..................................................................................... 26 5.4 Impacts on Drainage ........................................................................................ 27 6.0 PROPOSED FLOOD MANAGEMENT MEASURES ................................................... 28 6.1 Flood Mitigation & Resilience Measures ........................................................ 28 6.2 Residual Flood Risk Management .................................................................. 29 6.3 Flood Defence Consent ................................................................................... 30 7.0 SURFACE WATER MANAGEMENT STATEMENT ................................................... 31 7.1 Key Principles ................................................................................................... 31 7.2 Existing Surface Water Drainage Regime ...................................................... 31 7.3 Sustainable Drainage ....................................................................................... 32 7.4 Surface Water Treatment ................................................................................. 35 7.5 Surface Water Attenuation Storage Requirements ....................................... 36 SLR JH Walter LLP ii SLR Ref. 408.03643.00033 Tongue End AD Plant, Deeping St. Nicholas: FRA & SWDS April 2016 7.6 SuDS Maintenance Responsibilities ............................................................... 37 8.0 PRINCIPAL OPERATION AND MAINTENANCE REQUIREMENTS ......................... 38 8.1 Overview ........................................................................................................... 38 8.2 Piped Systems (including gullies and kerb drainage) .................................. 38 8.3 Detention Basins and Lagoons ....................................................................... 39 8.4 Permeable Paving ............................................................................................ 40 9.0 CONCLUSION ............................................................................................................. 41 10.0 CLOSURE .................................................................................................................... 43 FIGURES Figure 1-1 Site Location Plan .............................................................................................. 1 Figure 1-2 View of Site from Counter Drain Drove (Looking South) ............................... 2 Figure 1-3 River Glen and Flood Defence Embankment .................................................. 3 Figure 1-4 Counter Drain and Raised Southern Bank (Looking North East) .................. 4 Figure 1-5 Delph Drain from Site Access (Looking South West) .................................... 4 Figure 1-6 Delph Drain Diversion (Looking South East Along SW Site Boundary) ....... 5 Figure 1-7 Extract of the Environment Agency Flood Map for Planning ........................ 8 Figure 1-8 Extract of South Holland SFRA Figure 7 – Flood Zones ................................ 9 Figure 4-1 EA Surface Water Depth Map - High Probability of Occurring .................... 18 Figure 4-2 EA Surface Water Depth Map - Medium Probability of Occurring .............. 19 Figure 4-3 EA Surface Water Depth Map - Low Probability of Occurring ..................... 20 Figure 4-4 EA Reservoir Flood Risk ................................................................................. 22 Figure 5-1 SFRA ‘Actual Risk’ Predicted Flood Depth (Future with Climate Change) 26 Figure 7-1 Four Pillars of SuDS (after CIRIA Report C753) ............................................ 33 TABLES Table 1-1 Flood Risk Vulnerability and Flood Zone ‘Compatibility’ ............................ 10 Table 3-1 Potential Risk Posed by Flooding Sources .................................................. 15 Table 5-1 National Precautionary Climate Change Sensitivity Ranges (2013) ........... 24 Table 5-2 Peak River Flow Allowances By River Basin District (2016) ....................... 25 Table 5-3 National Precautionary Climate Change Sensitivity Ranges (2016) ........... 25 Table 7-1 Greenfield Runoff Analysis ............................................................................ 32 Table 7-2 Proposed Site Land Use ................................................................................. 35 Table 7-3 Summary of Post-Development Attenuation Storage Volumes .................. 37 Table 8-1 Typical Pipe System Maintenance Requirements ........................................ 38 Table 8-2 Typical Basin / Lagoon Maintenance Requirements .................................... 39 Table 8-3 Typical Permeable Paving Maintenance Requirements .............................. 40 APPENDIX Appendix A Topographical Survey Appendix B Internal Drainage Board Watercourse Map Appendix