Borough of Poole Flood Risk Management Strategy
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Borough of Poole Flood Risk Management Strategy Borough of Poole January 2011 Final Report 9V4473 All rights reserved. No part of this publication may be reproduced in any form, including photocopying or, transmitted by electronic means, or stored in an electronic retrieval system without express permission in writing from the Borough of Poole. This report has been prepared by Haskoning UK Ltd. solely for the Borough of Poole in accordance with the terms of appointment for the Poole Flood Risk Management Strategy proposal dated May 2009 and should not be relied upon by third parties for any use whatsoever without express permission in writing from the Borough of Poole. All maps in this publication may be based upon Ordnance Survey material with the permission of Ordnance Survey on behalf of the Controller of HMSO © Crown Copyright. Unauthorised reproduction infringes Crown copyright and may lead to prosecution or civil proceedings. 10024248. 2010. Additional information © Borough of Poole A COMPANY OF HASKONING UK LTD. COASTAL & RIVERS Stratus House Emperor Way Exeter, Devon EX1 3QS United Kingdom +44 (0)1392 447999 Telephone 01392 446148 Fax [email protected] E-mail www.royalhaskoning.com Internet Document title Borough of Poole Flood Risk Management Strategy Document short title Borough of Poole SFRM Status Final Report Date January 2011 Project name Poole SFRM Project number 9V4473 Client Borough of Poole Reference 9V4473/R/303581/Exet Drafted by Duncan Riches / Rachel Bird Checked by Steve Edwards Date/initials check …………………. …………………. Approved by Steve Edwards Date/initials approval …………………. …………………. SUMMARY This study has been produced by Royal Haskoning for the Borough of Poole (BoP), in consultation with the Environment Agency (EA). It is a strategic review of flood risk to 100 years beyond the end of the forthcoming Core Strategy (2126). The purpose is to provide a robust and defendable long term framework to inform decisions on flood risk issues relating to BoP planning policy. In this way the continued development of key sites in the Borough can help in the approach of obtaining contributions towards future improved flood defences. Flood defence measures that meet the policies determined by the recently completed Shoreline Management Plan (SMP) have been identified and costed in outline to inform this study. Raised defences have been identified, as these meet the SMP policies and continue current practice. A number of other types of measures are discussed, and it may be that the current comprehensive Environment Agency Poole and Wareham Flood and Coastal Erosion Risk Management Strategy recommends a different approach at some locations when it reports in 2 years time. The aim of this strategy study is to determine a realistic and workable option for defending the area both now and in the future from tidal flooding. The measures assessed within this report may not be the optimum solution but do provide a sensible estimate of the potential costs of a flood defence scheme for Poole. This allows the Borough of Poole to start planning and securing finances to ensure the funding is in place when defences are required. The study area, as shown in Figure 1.1, is defined by the Borough’s administrative boundary which intersects with the coast in the east near Canford Cliffs and the west, mid way about Poole Harbour in Lytchett Bay. The low lying nature of the frontage means that many of the wards of the Borough of Poole are subject to flood risk. Recent modelling for the Borough of Poole Strategic Flood Risk Assessment (SFRA) Level 2 study, completed in July 2008, highlighted that there are currently 504 properties at risk from tidal flooding from a 1 in 200 year event in Poole and that this number will increase to over 4,000 in the future due to sea level rise. In addition to the existing properties, flood risk needs to be considered in terms of new developments. The Borough of Poole’s emerging Core Strategy covers the period up to 2026. When considering future development within the Core Strategy the requirements of Planning Policy Statement 25: Development & Flood Risk (PPS25) must be met. To do this the Borough needs to ensure that any development highlighted in the Core Strategy will not be at excessive flood risk during its entire lifetime. For residential development this is assessed to be 100 years. This means that the effects of climate change on flood defence issues need to be considered, at least up to the year 2126. Current guidance from Defra suggests that sea levels could rise by up to 1.26m by 2126. This means that by 2126 there could be 4,039 properties at risk of tidal flooding in Poole. The indicative standard of protection for coastal areas is 1 in 200 years, as specified in Defra guidance. For this study we have consequently established that significant flood risk management measures will be required to provide a 1 in 200 year standard of protection to the whole area in 2126. Currently flood defences are present at strategically important locations, including Poole Town Quay and Hamworthy. These assets are less than ten years old and were Borough of Poole SFRM - i - 9V4473/R/303581/Exet Final Report January 2011 constructed by the Environment Agency. Defences at other locations around the harbour are a mixture of private and defacto defences (e.g. railway embankments and slipways). Based on the sea level rise predictions this study has developed measures for the management of flood risk over the next 116 years. The study area has been split into discrete cells to determine the potential measures required to protect that particular cell. It does not look into the effects of fluvial or surface water flooding although the potential impact of these is considered in the development of measures. An outline assessment of the cost of the proposed works was undertaken using information from recent completed schemes and the Environment Agency unit cost database as well as our own databases and engineering judgement. The total cost of the proposed flood risk management infrastructure for the entire study area equates to a capital cost of approximately £158 million. An economic assessment was undertaken based on the number of properties at risk and average property damage values, using information from the Multicoloured Manual (MCM). This only focuses on the damage to the actual property and not indirect impacts on the area, such as loss of tourism. This is particularly relevant in this area and should be highlighted as part of a funding application. In line with Defra and HM Treasury rules, the economic assessment only considers the existing land use for the area. Potential damages to planned developments are not taken into account. Results indicate that over the lifetime of the Borough of Poole’s Core Strategy, present value benefits for a scheme protecting up to a 200 year flood event amounts to approximately £157 million in 2010. This value then increases significantly if the work is undertaken at a later date, rising to £1,128 million for a scheme constructed in 2126. This significant increase is a result of the predicted rise in sea level due to climate change, as both the quantity of houses affected and the depth of flooding is greater. This provides an overall benefit cost ratio of 1 currently, rising to 7.2 for a scheme in 2126. This suggests that in the future a scheme for the whole area would be economically viable. This FRM strategy demonstrates that although considerable additional flood defence measures are required to provide a 1 in 200 year standard of protection in 2126, there is a compelling economic argument to do so. This means that development can be permitted and regeneration continue in the town centre despite the threat of sea level rise and that as sea levels continue to rise measures can be put in place as required. The table overleaf provides details of the benefit cost ratio for potential flood defence schemes split across the different cells for five epochs. This helps to highlight that it is viable to undertake work in some cells sooner than others and therefore this can be a tool for prioritising the works required. 9V4473/R/303581/Exet - ii - Borough of Poole SFRM January 2011 Final Report Year the scheme is undertaken Cell 2010 2035 2060 2086 2126 1 0.3 0.8 1.8 3.4 5.4 2 1.5 2.5 4.0 6.0 7.9 3 2.1 4.6 10.6 20.1 30.0 4 1.0 1.9 3.7 6.1 8.7 5 0.8 1.5 3.0 5.0 6.9 6 0.3 0.5 0.9 1.5 2.1 All cells 1.0 1.8 3.2 5.2 7.2 Red indicates that cost is greater than potential benefit, orange indicates that the benefits outweigh the cost but that Defra funding is unlikely, whilst green highlights where it may be possible to obtain Defra funding for the works. Note – Defra funding opinion is based on current guidance. Based on purely economic viability cell 3 looks to be the most appropriate area to focus initial work, although there are other factors that also influence the timing of when a scheme is undertaken. This includes the condition of the existing defences and the potential for regeneration in the area. Regeneration provides the possibility of obtaining developer contributions for the required works and therefore reducing the impact on the public purse. The potential to obtain such contributions may well bring the scheme to the fore. No large redevelopment areas are proposed within cell 3 and therefore most of the funding would have to be from public sources, therefore it would not receive flood defence Gant in Aid (FDGiA) until well after 2035.