2 5. Flood Consequence Assessment Brechfa Forest Connection Development Consent Order Application - Reference EN020016 Flood Consequence Assessment May 2015 Regulation reference: The Infrastructure Planning (Applications: Prescribed Forms and Procedure) Regulations 2009 Regulation 5(2)(e) Flood Consequence Assessment – Volume 5.2 Contents 1 Introduction 4 2 Context and scope of work 6 3 Legislation and policy context 8 4 TAN 15 11 5 Sources of information/consultation 13 6 Climate change 15 7 Nant Pibwr Crossing 16 8 Flood mitigation measures – Nant Pibwr 24 9 Planning Context 27 10 Site description – Towy/Gwili floodplain 30 11 Flood mitigation measures – Towy/Gwili floodplain 45 12 Planning context 50 13 Site description – River Gwili crossing 54 14 Flood mitigation measures – River Gwili 63 15 Planning context 67 16 Conclusions and recommendations 70 17 References 72 1 Flood Consequence Assessment – Volume 5.2 Tables Table 3.1: National legislation and policy context 8 Table 3.2: LDF policy context 10 Table 5.1: Relevant studies 13 Table 7.1: NRW modelled river levels (mAOD) for the Nant Pibwr node NP6 21 Table 10.1: NRW modelled river levels (mAOD) for the River Towy (nodes AT*) and River Gwili (nodes AG*) 36 Table 10.2: Predicted flood levels at works locations 38 Table 10.3: Present day tidal levels for at Carmarthen Quay 40 Table 11.1: Danger to people for different combinations of depth and velocity 48 Table 13.1: NRW modelled river levels (mAOD) for the River Gwili 59 Figures Figure 7.1: Site location plan 16 Figure 7.2: TAN15 Development Advice Map (accessed April 2015) 19 Figure 7.3: Environment Agency surface water flood map (accessed April 2015) 22 Figure 10.1: Site location plan 31 Figure 10.2: TAN15 Development Advice Map (accessed April 2015) 35 Figure 10.3: Environment Agency surface water flood risk map (accessed April 2015) 41 Figure 10.4: Environment Agency reservoir flood map (accessed April 2015) 43 Figure 13.1: Site location plan 55 Figure 13.2: TAN15 Development Advice Map (accessed April 2015) 58 Figure 13.3: Environment Agency surface water flood map (accessed April 2015) 60 2 Flood Consequence Assessment – Volume 5.2 Appendices Appendix A – RSK Service Constraints Appendix B – Natural Resources Wales flood level data Appendix C – Nant Pibwr crossing plans Appendix D – Towy/Gwili Floodplain crossing plans Appendix E – River Gwili crossing plans Appendix F – Natural Resources Wales correspondence 3 Flood Consequence Assessment – Volume 5.2 1 Introduction 1.1.1 RSK Land and Development Engineering Ltd (RSK) was commissioned to carry out a Flood Consequence Assessment (FCA) for WPD (Client). The assessment is in support of the Environmental Impact Assessment as part of a planning submission to PINS for the proposed development. 1.1.2 The assessment has been prepared in accordance with Planning Policy Wales (PPW) (Ref. 1) and the Technical Advice Note 15 (TAN 15) (Ref. 2), the Interim Code of Practice for Sustainable Drainage (Ref. 3) and BS 8533-2011 Assessing and Managing Flood Risk in Development Code of Practice (Ref. 4), with site- specific advice from the Natural Resources Wales (NRW), Carmarthenshire County Council (CCC) and the client. 1.1.3 The NPPF sets out the criteria for development and flood risk by stating that inappropriate development in areas at risk of flooding should be avoided by directing development away from areas at highest risk, but where development is necessary, making it safe without increasing flood risk elsewhere. The key definitions are: . “Areas at risk of flooding” means land within Flood Zones B and C1 or C2; or land within Flood Zone A which has critical drainage problems and which has been notified to the local planning authority by NRW; and . “Flood risk” means risk from all sources of flooding including from rivers and the sea, directly from rainfall on the ground surface and rising groundwater, overwhelmed sewers and drainage systems, and from reservoirs, canals and lakes and other artificial sources. 1.1.4 For this Flood Consequences Assessment three locations are being assessed: . OHL crossing of the Nant Pibwr north of the A48; . HDD and Open Trench works within the Towy/Gwili floodplain between 4 Flood Consequence Assessment – Volume 5.2 Carmarthen and Abergwili; and . OHL crossing of the Gwili between Llanpumsaint and LLanllawdogg. 1.1.5 For this site, the key aspects that require the assessment are: . The NRW’s Development Advice Map shows that these locations cross or are located within Flood Zones B or C2. 1.1.6 The comments given in this report and opinions expressed are subject to RSK Group Service Constraints provided in Appendix A. 5 Flood Consequence Assessment – Volume 5.2 2 Context and scope of work 2.1.1 A key element of project development is to prepare a FCA to establish the flood risk associated with the proposed development and to propose suitable mitigation, if required, to reduce the risk to a more acceptable level. 2.1.2 The scope of work relating to a FCA is based on the guidance provided in Chapter 13 of Planning Policy Wales (Ref. 1) and its accompanying Technical Advice Note (TAN) 15 (Ref. 2). 2.1.3 A site-specific FCA must demonstrate that the development will be safe for its lifetime taking account of the vulnerability of its users, without increasing flood risk elsewhere, and, where possible, will reduce flood risk overall. The scope of this assessment therefore comprises the following elements: . to review architect plans, planning information and other studies to determine existing site conditions; . to obtain information on the hydrology and hydrological regime in and around the site; . to obtain the views of the NRW including scope, location and impacts; . to determine the extent of new flooding provision and the influence on the site; . to assess the impact on the site from climate change effects and anticipated increases in rainfall over a 60 year period for the energy infrastructure (poles) and over a nine month period (undergrounding civils operations being completed within an estimated two months and a further one month for cable installation, i.e. cable pulling through the ducts) period for the temporary works and compounds in the Towy/Gwili location and for the working areas associated with the pole erection at the Nant Pibwr and River Gwili crossings; . to review site surface water drainage based on the proposed layout and, if necessary, to determine the extent of infrastructure required; 6 Flood Consequence Assessment – Volume 5.2 . to provide mitigation measures to protect the safety of the users and the equipment at the temporary compounds and works locations; and . to prepare a report including calculations and summaries of the source information and elements reviewed. 2.1.4 This report is in support of the following key reports and information: . Environmental Impact Assessment (Ref. 5) carried out by RSK for WPD. 2.1.5 Reliance has been place on factual and anecdotal data obtained from the sources identified. RSK cannot be held responsible for the scope of work, or any omissions, misrepresentations, errors or inaccuracies with the supplied information. New information, revised practices or changes in legislation may necessitate the re-interpretation of the report in whole or in part. 7 Flood Consequence Assessment – Volume 5.2 3 Legislation and policy context 3.1 National policy Table 3.1: National legislation and policy context Legislation Key provisions Planning Policy Wales (PPW) contains guidance considered relevant to the scope of the environmental assessment. PPW is supported by a number of Technical Advice Notes (TANs). Flood Risk and climate change are considered in section 13.2, this section highlights that flood risk is a material consideration. Paragraph 13.2.4 highlights that “meeting the Welsh Government’s objectives for sustainable development requires action through the planning system to move away from flood defence and mitigation of the consequences of new development in areas of flood hazard towards a more positive avoidance of development in areas defined as being of flood hazard.” Section 13.4 addresses development management and flood risk, this section highlights the NPS, stating that “development proposals in areas defined as high flood hazard should only be considered: new development can be justified in that location, even though it is likely to be at risk from flooding; and the development proposal would not result in the Planning Policy Wales (Ref. 1) intensification of existing development which may itself be at (2014) risk; and new development would not increase the potential adverse impacts of a flood event. Section 13.12 considers development management and improvements to the quality of water and air. It states that pollution affecting the use of land will be a material consideration and will include location, impact on health and amenity, risk to the surrounding environment, prevention of nuisance, impact on the transport network and the need, where relevant, and feasibility of restoring the land to standard sufficient for an appropriate use. Section 13.10 of PPW highlights the need to improve water and air quality. Paragraph 13.10.1 states that: “The planning system should determine whether a development is an acceptable use of land and should control other development in proximity to potential sources of pollution rather than seeking to control the processes or substances used in any particular development”. Technical Advice Note (TAN) 15 technical guidance which Technical Advice Note 15 supplements the policy set out in Planning Policy Wales in relation to (Ref. 2) development and flooding. TAN 15 provides advice on: 8 Flood Consequence Assessment – Volume 5.2 . development advice maps; . nature of development or land use; . justifying the location of built development; . assessing flooding consequences; .