Flood Risk Assessment
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North and North East Lincolnshire Strategic Flood Risk Assessment November 2011 Strategic Flood Risk Assessment November 2011 Contents 1 Terms of Reference 1 Background Information 1 The Study Area 1 Scope (and limitations) of the Review 2 Changes introduced by PPS25 2 Other information now available or in preparation 3 Topics covered by the Review 3 2 Planning Policy Context 5 Introduction 5 National Policy 5 Regional Policy 6 Local Policy 7 3 Assessing Flood Risk 9 Factors affecting Flood Risk 9 Flood Zones and Flood Maps 9 Aims of PPS25 10 The Sequential Test 12 The Exception Test 12 The Practice Guide to PPS25 14 Preparing a Strategic Flood Risk Assessment 15 Preparing a Site-Specific Flood Risk Assessment 16 4 Study Methodology 17 Sources of Data 17 Existing Flood Risk 17 Ground Levels 17 Flooding from the sea 17 Flooding from rivers 18 Flooding from other sources 18 Historic flooding 18 Existing flood defences and related information 19 Climate change allowances 19 Breach parameters 19 The Level 1 Assessment 20 Flooding from the sea (estuary) 20 Flooding from rivers 20 Functional floodplain 20 I Strategic Flood Risk Assessment November 2011 Flooding from other sources 21 The Level 2 Assessments 21 5 Outcome of Level 1 Assessment 23 Eastern Coastal Area 24 Location, extent and development potential 24 Main sources of flooding 24 Flood compartments 25 Ancholme Valley Area 26 Location, extent and development potential 26 Main sources of flooding 27 Flood compartments 28 Trent Valley Area 29 Location, extent and development potential 29 Main sources of flooding 30 Flood compartments 32 6 Outcome of Level 2 Assessments 35 Flood Compartment 1T1 – Cleethorpes 36 Flood Compartment 1T2 – Grimsby and Stallingborough 36 Sub-Compartment 1 – Grimsby Docks and Grimsby 36 Sub-Compartment 2 – Stallingborough 37 Flood Compartment 1T3 – Immingham andNorth Killingholme 37 Sub-Compartment 1 – Immingham 38 Sub-Compartment 2 – Killingholme Marshes 38 Sub-Compartment 3 – Halton Marshes 38 7 Planning Guidance 39 Flood Risk Standing Advice 39 8 Guidance on the use of Sustainable Drainage Systems 41 Introduction 41 Types of sustainable drainage systems 41 Use of SUDS techniques in North and North East Lincolnshire 41 9 Additional Considerations 43 Implications of Flood and Water Management Act 43 Preparation of Local Flood Risk Management Strategy 43 Procedure for reviewing the SFRA 44 II Strategic Flood Risk Assessment November 2011 Appendix A - PPS25 Practice Guide 45 Appendix B - Factors Affecting Flood Risk 47 Tidal flooding 47 Fluvial flooding 47 Surface and groundwater flooding 48 Future changes 49 Appendix C - PPS25 Flood Zones and Flood Risk Vulnerability Classification 51 From PPS 25 Table D.2 - Flood Risk Vulnerability Classification 55 Appendix D - Critical Flood Levels 57 Introduction 57 Appendix E - Local Planning Guidance 61 Introduction 61 Background 61 Flood Risk Assessment 62 Sequential and Exception Tests 62 Undertaking the Sequential and Exception Tests 63 Environment Agency Standing Advice 67 Process for deciding a planning application 68 Flood Risk Assessments accompanying planning applications 69 Approvals and refusals of planning applications 70 North & North-East Lincolnshire Flood Risk Standing Advice Flood Risk Response Matrix November-2011 71 Appendix F - Mitigation Measures 85 Introduction 85 Possible mitigation measures in SFRA Flood Zone 2/3(a) 85 Raising floor levels 85 Raising ground levels 85 Providing flood defences 85 Providing upstairs accommodation or place of safety 86 Using flood resistant construction techniques 86 Using flood resilient construction techniques 86 Possible mitigation measures in areas subject to surface water flooding 87 Managing surface water inflows to the site 87 Improving the existing drainage network 87 Appendix G - Types of Sustainable Drainage Systems 89 Introduction 89 Types of sustainable drainage systems 89 Permeable surfaces 89 Green roofs 89 III Strategic Flood Risk Assessment November 2011 Filter drains 89 Filter strips 90 Swales 90 Basins 90 Infiltration devices 90 Bio-retention areas 90 Pipes and accessories 90 Appendix H - Eastern Coastal Area Flood Compartments 91 General Description of Area 91 Location, extent and development potential 91 Main sources of flood risk 91 Flood compartments 93 1T1: Cleethorpes 94 Description of site 94 Sources of flood risk 95 Existing defences 95 1T1 Supplementary Assessment: Humberston Fitties 96 Description of site 96 Sources of flood risk 96 Existing flood defences 97 Assessment of flood risk 98 1T2: Grimsby & Stallingborough 98 Description of site 98 Sources of flood risk 99 Existing defences 100 1T3: Immingham and North Killingholme 101 Description of site 101 Sources of flood risk 101 Existing defences 102 1T4: Goxhill 103 Description of site 103 Sources of flood risk 104 Existing defences 104 1T5: Barton upon Humber 105 Description of site 105 Sources of flood risk 106 Existing defences 106 IV Strategic Flood Risk Assessment November 2011 1F1: Waithe Beck 107 Description of site 107 Sources of flood risk 107 Existing defences 107 1F2: Buck Beck and Goosepaddle Drain 107 Description of site 107 Sources of flood risk 108 Existing defences 108 1F3: River Freshney and Laceby Beck 108 Description of site 108 Sources of flood risk 108 Existing defences 109 1F4 East Halton Beck and Skitter Beck 109 Description of site 109 Sources of flood risk 109 Existing defences 109 1F5: Barrow Beck and Midby Drain 110 Description of site 110 Sources of flood risk 110 Existing defences 110 Appendix I - Ancholme Valley Flood Compartments 111 General Description Of Area 111 Location, extent and development potential 111 Main sources of flood risk 111 Flood compartments 114 2T1: South Ferriby (East) 115 Description of site 115 Sources of flood risk 116 Existing defences 116 2T2: South Ferriby (West) 117 Description of site 117 Sources of flood risk 117 Existing defences 117 2T3: Winterton 118 Description of site 118 Sources of flood risk 118 Existing defences 118 V Strategic Flood Risk Assessment November 2011 2F1: Lower Ancholme Right Bank 119 Description of site 119 Sources of flood risk 119 Existing defences 119 2F2: Lower Ancholme Left Bank 120 Description of site 120 Sources of flood risk 120 Existing defences 121 2F3: Island Carr 121 Description of site 121 Sources of flood risk 121 Existing defences 121 2F4: Middle Ancholme (Right Bank) 122 Description of site 122 Sources of flood risk 122 Existing defences 122 2F5: Middle Ancholme (Left Bank) 123 Description of site 123 Sources of flood risk 123 Existing defences 123 Appendix J - Trent Valley Flood Compartments 125 General Description of Area 125 Location, extent and development potential 125 Main sources of flood risk 125 Flood compartments 129 3T1: Alkborough 131 Description of site 131 Sources of flood risk 131 Existing defences 131 3T2: Flixborough 131 Description of site 131 Sources of flood risk 132 Existing defences 132 3T3: Gunness 132 Description of site 132 Sources of flood risk 132 Existing defences 133 VI Strategic Flood Risk Assessment November 2011 3T4: Garthorpe & Keadby 133 Description of site 133 Sources of flood risk 133 Existing defences 134 3F1: Upper Bottesford Beck 134 Description of site 134 Sources of flood risk 135 Existing defences 135 3F2: Messingham 135 Description of site 135 Sources of flood risk 135 Existing defences 136 3F3: Upper River Eau 136 Description of site 136 Sources of flood risk 136 Existing defences 136 3F4: Three Rivers 136 Description of site 136 Sources of flood risk 137 Existing defences 137 3F5: Isle of Axholme 138 Description of site 138 Sources of flood risk 138 Existing defences 139 3F6: River Idle 139 Description of site 139 Sources of flood risk 139 Existing defences 140 VII Strategic Flood Risk Assessment November 2011 List of Maps 1. Study area 2. Environment Agency’s flood zone map 3. Ground level source data 4. Digital ground model (DGM) 5. Internal drainage board boundaries and drainage systems 6. Historic flooding 7. Location of breaches in breach hazard studies 8. Eastern Coastal Area – IDBs, watercourses and pumping stations 9. Eastern Coastal Area – Flood compartments 10. Ancholme Valley Area – IDBs, watercourses and pumping stations 11. Ancholme Valley Area – Flood compartments 12. Trent Valley Area – IDBs, watercourses and pumping stations 13. Trent Valley Area – Flood compartments 14. Compartment 1T1; Cleethorpes – Ground levels 15. Compartment 1T2; Grimsby and Stallingborough – Ground levels 16. Compartment 1T3; Immingham and North Killingholme – Ground levels Maps for Appendix D 17 Eastern Coastal Area, Critical Flood Levels 18 Ancholme Valley Area, Critical Flood Levels 19 Trent Valley Area, Critical Flood Levels SFRA Flood Zone Maps 20 Eastern Coastal Area SFRA Flood Zones 21 Ancholme Valley Area SFRA Flood Zones 22 Trent Valley Area SFRA Flood Zones Breach Hazard Maps 23. Compartment 1T1; Cleethorpes Breach Hazard 24 Compartment 1T2; Grimsby and Stallingborough Breach Hazard 25 Compartment 1T3; Immingham and North Killingholme Breach Hazard VIII Strategic Flood Risk Assessment November 2011 1 Terms of Reference Background Information 1.1 In November 2006, North East and North Lincolnshire Councils (NE/NLC) published their Strategic Flood Risk Assessment (SFRA), prepared in accordance with Planning Policy Guidance 25 (PPG25) – Development and Flood Risk. This document provided the planning authorities with the information they needed to make objective judgements about flooding, both when making decisions on land allocations for development plans and when deciding planning applications for development in their areas. 1.2 Since the SFRA was published Planning Policy Statement 25 (PPS25) has replaced PPG25, providing revised guidance on how to assess flood risk. In addition more detailed information has been produced allowing the earlier assessment to be improved. 1.3 The two councils need the SFRA to be updated so they can prepare Core Strategy and other documents required for their Local Development Frameworks (LDFs). Accordingly the councils have asked RYE Consultancy to review the SFRA taking into account the policy changes introduced in PPS25 and the other information currently to hand, as discussed later in this section.