4. Strategic Flood Risk Assessments
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15 4. Strategic Flood Risk Assessments 4.1 Objectives Historically, the management of flood risk in the UK has been undertaken in a somewhat reactive manner, addressing problems on an ‘as needed’ basis in response to a flooding event. It was recognised by Government that, in general, this was not a particularly cost effective approach and often failed to consider individual problem areas within the bigger picture of the wider hydrological system. The Environment Agency has therefore committed to a rolling programme of flood risk assessment (mapping) and strategic flood risk management investigations, including Catchment Flood Management Plans (CFMPs) and PAG2 Flood Risk Management Strategies5 within fluvial (river) systems. These studies take a catchment-wide approach, identifying where flooding is known and/ or perceived to be an existing problem, how this flooding regime may alter in future years as a result of climate and land use change, and how flooding can be managed cost effectively and sustainably over the next 50 to 100 years. On a local planning level, SFRAs consider the flood risk within the local area and, through the Sequential Test detailed in PPG 25 and the emerging PPS 25, allow LPAs such as Pendle Borough Council to direct development whilst controlling flood risk. More detailed Flood Risk Assessments (FRAs) would then be undertaken for the selected sites when and if they are developed. The SFRA should not contradict broader catchment scale recommendations of a CFMP and planning directed by the SFRA should fit within CFMP objectives. However, since SFRAs are specific to administrative areas they can pay more attention to secondary sources of flooding (such as overland flow, sewer and groundwater flooding) than CFMPs. 4.2 General Approach 4.2.1 Introduction The SFRA is a planning tool. It is an assessment of flood risk to inform the spatial planning process, and therefore the degree of detail and accuracy should be commensurate with this objective. A pragmatic and risk-based approach is recommended. The assessment of flood risk within a Borough should be targeted to those areas where development pressure is proposed within current planning horizons. Furthermore, the accuracy sought with respect to the delineation of flood risk should be sufficient to ensure confidence in the findings and recommendations of the SFRA, and it should also be reasonable within the context of the intended end use of the document to inform the allocation of sites within the LDF. 5 FCDPAG2 Strategic Planning and Appraisal, part of the series Flood and Coastal Defence Project Appraisal Guidance, DEFRA, April 2001. h:\projects\hm-250\18108 pendle sfra\docs\stage 2 report\rr057i3.doc © Entec UK Limited 30 October 2006 16 The LPA, supported by advice from the Environment Agency, must ensure flood risk is managed appropriately and effectively during the planning process. To facilitate this, and to inform the planning process, the ODPM expects LPAs to undertake a sequential flood risk test when planning development as outlined in PPG 25 and the emerging PPS 25. PPS 25 states (section 2, paragraph 13): “A sequential approach to determining the suitability of land for development in flood risk areas is central to the guidance and should be applied at all levels of the planning process.” 4.2.2 The PPS 25 Sequential Test and Exception Test PPS 25 sets out a robust approach to the Sequential Test that is core to the SFRA process and intended to provide a rigorous understanding of local flood risk. It is based on Environment Agency flood zones, which delineate areas by their level of risk due to river and sea flooding. Table 4.1 summarises these zones. Table 4.1 PPS 25 Flood Risk Zones Zone Criteria Appropriate Land Use Vulnerability 1 Zone 1 Land with a < 0.1% chance of river All land uses and sea flooding in any year. Low Probability Zone 2 Land with between a 1% and 0.1% Water compatible, less vulnerable and more vulnerable chance of river flooding or land uses Medium Probability between a 0.5% and 0.1% chance of sea flooding in any year. Highly vulnerable land uses only if the Exception Test is passed Zone 3a 2 Land with a > 1% chance of river Water compatible and less vulnerable land uses flooding or a > 0.5% chance of sea High Probability flooding in any year. More vulnerable land uses and essential infrastructure only if the Exception Test is passed No highly vulnerable land uses Zone 3b 3 Land where water has to flow or Water compatible land use be stored in times of flood. Functional Floodplain Essential infrastructure only if it must be in this location and the Exception Test is passed No less vulnerable, more vulnerable or highly vulnerable land uses 1 See Appendix B for land use vulnerability classification. 2 PPG 25 Zones 3a and 3b have been merged into PPS 25 Zone 3a. 3 PPG 25 Zone 3c is PPS 25 Zone 3b. h:\projects\hm-250\18108 pendle sfra\docs\stage 2 report\rr057i3.doc © Entec UK Limited 30 October 2006 17 The overriding aim of the Sequential Test is to steer all new development to the lowest flood risk zone (i.e. zone 1). Where it is not possible to locate development in zone 1, development may be considered in zone 2 and then zone 3 if there is no available alternative in a lower risk zone. The Sequential Test constrains such development based on the vulnerability of the proposed land use, with the more vulnerable land uses restricted to zones of lower risk. Table 4.1 indicates the appropriate land use vulnerabilities for each zone. Appendix B lists land uses according to the vulnerability classification used in the Sequential Test. Depending on the land use vulnerability, there may be a further requirement to satisfy the Exception Test outlined in PPS 25 prior to development in these higher risk zones (as indicated in Table 4.1). “The Exception Test is that: a) The development makes a positive contribution to sustainable communities, and to sustainable development objectives of the relevant LDD…; b) The development is on developable brownfield land or where there are no reasonable alternative options on developable brownfield land; c) A flood risk assessment demonstrates that the residual risks of flooding to people and property (including the likely effects of climate change) are acceptable and can be satisfactorily managed; and d) The development makes a positive contribution to reducing or managing flood risk.” The Exception Test should be applied as early in the planning process as possible, and should not be used to justify ‘highly vulnerable’ development in zone 3a, or ‘less vulnerable’, ‘more vulnerable’ or ‘highly vulnerable’ development in zone 3b. Where development is planned in the higher risk zones, flood management and mitigation measures may be required to reduce risks to an acceptable level. Types of measures could range from traditional flood defences and flood alleviation schemes, to flood resistant and resilient design, and emergency plans. Where either existing or proposed measures are in place, the Sequential Test requires a demonstration that the residual flood risk (i.e. after taking the management and mitigation measures into account) is acceptable. In addition, the potential for climate change to impact on flood risk must also be considered. Development in all zones, both low and high risk, must also consider flood risks other than those due to river and sea flooding (e.g. overland flow, sewer and groundwater flooding) and apply a sequential approach to these risks if present. In addition, the implications the development has for flood risk elsewhere due to its drainage and runoff must also be considered. The application of the Sequential Test taking land use vulnerability into account, together with the Exception Test, forms a rigorous process for assessing and prioritising the location of planned development with respect to flood risk. If required, the Sequential Test can be undertaken as an iterative process, using greater resolution and understanding of the flood risks, and after testing how effective any management or mitigation measures might be. In the context of an SFRA, the application of the Sequential Test is restricted to a strategic level to inform the spatial planning process. The specific flood risk issues associated with potential development sites identified through the SFRA process will then be assessed in more detail via a site-specific FRA as part of the planning application. h:\projects\hm-250\18108 pendle sfra\docs\stage 2 report\rr057i3.doc © Entec UK Limited 30 October 2006 18 4.3 Approach for Pendle Borough The following key factors relating to development and flood risk influenced how the SFRA approach was tailored to Pendle Borough: • A history of significant fluvial flood events, but also known incidents of flooding due to other mechanisms, in particular overland flow and blockages or insufficient capacities of culverts and bridges; • Flood alleviation schemes on Walverden Water (planned) and Pendle Water (implemented); • The recent enmainment of nine critical ordinary watercourses (COWs) in the Borough; • Significant brownfield redevelopment and regeneration planned within the urban areas of Pendle Borough and potential new development of adjacent greenfield areas (see Section 2). As the principle aim of the Sequential Test is to locate development in the lowest flood risk zone, the Pendle SFRA emphasises the steering of planned development to zone 1 which is appropriate for all categories of land use vulnerability. Where no suitable alternative is available, there may be some scope for locating development in higher risk flood zones depending on the vulnerability of the proposed land use. Table 4.2 shows the PPS 25 criteria with respect to the vulnerability of planned development in Pendle Borough and appropriate levels of flood risk; Appendix B gives the full details of acceptable land uses for these vulnerability classifications.