NORTH LONDON WASTE AUTHORITY NORTH LONDON HEAT AND POWER PROJECT FLOOD RISK ASSESSMENT The Planning Act 2008 The Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009 Regulation 5 (2) (e) AD05.14 Amec Foster Wheeler Revision 0 October 2015 Any disclosure of this report to a third party is subject to this disclaimer. The report was prepared by Amec Foster Wheeler at the instruction of, and for use by our client, and takes into account the instructions and requirements of our client. It does not in any way constitute advice to any third party who is able to access it by any means. Amec Foster Wheeler excludes to the fullest extent lawfully permitted all liability whatsoever for any loss or damage howsoever arising from reliance on the contents of this report by any third party. We do not however exclude our liability (if any) for personal injury or death resulting from our negligence, for fraud or any other matter in relation to which we cannot legally exclude liability. North London Waste Authority North London Heat and Power Project Flood Risk Assessment Contents Page Executive summary 1 1 Introduction 4 1.1 Introduction 4 1.2 Purpose of this document 4 1.3 Document structure 5 1.4 The Applicant 5 1.5 The Application Site 6 1.6 Surrounding area 7 1.7 The Project 8 1.8 Stages of development 12 2 The existing Application Site 19 2.1 Application Site description 19 2.2 Topography 19 2.3 Hydrology 22 2.4 Existing drainage 24 2.5 Geology, hydrogeology and soils 24 3 Proposed ground cover 28 4 Planning context 29 4.2 National Policy Statement for Energy (NPS EN-1) 29 4.3 National Policy Statement for Renewable Energy Infrastructure (NPS EN-3) 30 4.4 National Planning Policy Framework 30 4.5 National Planning Policy Guidance 33 4.6 Strategic Flood Risk Assessment 33 4.7 Enfield Development Management Document 34 4.8 Enfield Local Flood Risk Management Strategy 34 4.9 London Plan 34 4.10 Environment Agency 35 4.11 Climate change 35 5 Flood risk 36 5.1 Potential sources of flood risk 36 5.2 Fluvial flood risk 36 5.3 Groundwater flood risk 40 5.4 Surface water flood risk 40 5.5 Sewer flooding 41 5.6 Artificial sources 42 AD05.04 | Issue | October 2015 | Amec Foster Wheeler E&I UK Ltd North London Waste Authority North London Heat and Power Project Flood Risk Assessment 6 Mitigation for flood risk 44 6.1 Fluvial flood risk 44 6.2 Artificial sources 53 7 Surface water management 54 7.1 Introduction 54 7.2 Preliminary Drainage Strategy 54 8 Conclusions 56 Tables Table 2.1: Summary of current land cover ........................................................... 19 Table 2.2: Depth and thickness of the clay layer at the Application Site .............. 25 Table 3.1: Ground cover at the Application Site ................................................... 28 Table 3.2: Ground cover for the Temporary Laydown Area ................................. 28 Table 4.1: Requirements of NPS EN-1 ................................................................ 29 Table 4.2: Flood Zone classification (Table 1 from National Planning Practice Guidance: Flood Risk and Coastal Change) ....................................... 31 Table 4.3 Flood Risk vulnerability classification (from Table 2 National Planning Practice Guidance: Flood Risk and Coastal Change) ......................... 32 Table 4.4: Flood Risk Vulnerability and Flood Zone Compatibility (Table 3 of National Planning Practice Guidance) ................................................. 32 Table 5.1: Summary of flood risks identified ........................................................ 36 Table 5.2: Modelled in-river flood levels adjacent to the Application Site (mAOD) – defended scenario ............................................................................... 39 Figures Figure 2.1: Site topography ................................................................................... 21 Figure 2.2: Hydrology features .............................................................................. 23 Figure 2.3: Source Protection Zones at the Application Site ................................. 26 Figure 5.1: Environment Agency Flood Zone mapping ......................................... 37 Figure 5.2: Flood mapping from the Environment Agency - defended scenario .... 38 Figure 5.3: Reservoir flood inundation zone modelled by the Environment Agency ............................................................................................................ 43 Figure 6.1: EcoPark House overlaid on flood map showing the 1 per cent AEP plus climate change defended flood extent ................................................. 45 Figure 6.2: Excerpt from Topography Survey – existing sea cadet building on the wharf ................................................................................................... 45 Figure 6.3: EcoPark House flood storage compensation ...................................... 46 Figure 6.4: EcoPark House flood storage compensation shown in wider site context ................................................................................................ 47 AD05.04 | Issue | October 2015 | Amec Foster Wheeler E&I UK Ltd North London Waste Authority North London Heat and Power Project Flood Risk Assessment Figure 6.5: Flood map showing the 1% AEP plus climate change defended flood extent .................................................................................................. 48 Figure 6.6: Excerpt from Topography Survey – existing car park .......................... 48 Figure 6.7: Existing and proposed Application Site layout – improved Advent Way access ................................................................................................. 48 Figure 6.8: Floodplain compensation area ............................................................ 50 Appendices Appendix A : Site Photos A.1 Appendix B : Environment Agency Correspondence and Flood Risk Information B.1 Appendix C : Preliminary Drainage Strategy C.1 Glossary Refer to Project Glossary (AD01.05) AD05.04 | Issue | October 2015 | Amec Foster Wheeler E&I UK Ltd North London Waste Authority North London Heat and Power Project Flood Risk Assessment Executive summary i.i.i This Flood Risk Assessment (FRA) has been prepared for the North London Heat and Power Project (the Project) at Advent Way, Enfield in North London. This report supports an application for a Development Consent Order (DCO). i.i.ii This FRA has been prepared in line with the National Planning Policy Framework (NPPF)1 and other relevant national, regional and local policy and guidance. The Environment Agency (EA) and London Borough Enfield (LB Enfield) have been consulted on the approach. i.i.iii Current EA flood risk mapping shows that most of the Application Site is located in Flood Zone 1, with the central section of Edmonton EcoPark within Flood Zone 2, i.e. there is a low probability of flooding across the majority of the Edmonton EcoPark, but some areas are at risk during an extreme fluvial flood (the 0.1 per cent Annual Exceedance Probability (AEP) event). The Temporary Laydown Area is entirely located within Flood Zone 2. Watercourses which are close to the Application Site are Enfield Ditch and Salmon’s Brook which are adjacent to Edmonton EcoPark, and the River Lee Navigation. The River Lee itself is located approximately 25m to the east of the Temporary Laydown Area. i.i.iv The Project is appropriate for Flood Zone 2. As such, the Exception Test does not need to be passed. The Sequential Test is deemed to be passed because the Application Site has been allocated for the current (and the proposed) use by LB Enfield in their development planning documents; the Edmonton EcoPark is already in use for waste processing and power generation and will continue to be used as such. There is, however, a remaining requirement to apply a sequential approach to the development within the red line boundary. i.i.v Once an allowance for climate change has been taken into account, three small areas of the Edmonton EcoPark are within the defended 1 per cent AEP flood extent. The first of these is on the wharf adjacent to the River Lee Navigation where EcoPark House is proposed. 11.0m3 flood storage compensation would be provided for loss of floodplain volume under the climate change scenario. Level for level storage would be provided on-site upstream of the wharf on the west bank of Enfield Ditch. Finished floor levels be set at or above 10.97m AOD, which incorporates a 300mm freeboard above the design flood level. The second area relates to a small existing car park in the southern section of the Application Site. Part of this is to be developed to provide an improved southern access road from Advent Way to the Edmonton EcoPark, and floodplain compensation is also proposed here. Approximately 107m3 of compensation would be provided on the northern bank of Enfield Ditch. The cross section of the new crossing over Enfield Ditch for the improved southern access would remain unchanged compared to that for the existing crossing, to ensure no impact elsewhere as a result of constriction of flows. The third area is located on 1 Department for Communities and Local Government (2012) National Planning Policy Framework, March 2012. Page 1 AD05.04 | Issue | October 2015 | Amec Foster Wheeler E&I UK Ltd North London Waste Authority North London Heat and Power Project Flood Risk Assessment the western edge of Edmonton Eco Park, associated with the flood extent of Salmon’s Brook. i.i.vi Upgrades are proposed to one crossing