Level 2 Strategic Flood Risk Assessment (.pdf ... - Wigan Council

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EA comment:Flood Risk GuidanceThe Practice Guide to PPS25 is very clear on this issue, in particular we would refer youto paragraphs 3.66 – 3.67 which state:“In general, the SFRA should aim to provide clear guidance on appropriate riskmanagement measures for adoption on potential sites within Flood Zones 2 and 3, whichare protected from flooding by existing defences, to minimise the extent to whichindividual developers need to undertake separate studies of the same problem e.g.breach and overtopping studies. In some instances improvements to existing flooddefences may be required to manage residual flood risks (see annex G of PPS25).Where such flood defence works are considered, the SFRA should include an appraisalof the extent of any works required to provide or raise the flood defence to an appropriatestandard.During the design event flooding will occur when bank levels are exceeded. Raisingexisting defences will not prevent flooding to these sites as they would simply bebypassed. To work, flood defences would need to be extended and the associateddrainage infrastructure enhanced to prevent flooding from other sources. As well as thecost implications of building new defences, the wide spatial distribution of potential sitesdoes not lend itself to a “single” style solution that could benefit a number of sites.The assessment addresses the Council requirements for an SFRA without becoming tooprescriptive in terms of stipulating detailed design requirements, we feel that this may limiteffective land use and innovative development. The guidance in the SFRA needs to bepragmatic and workable and the emphasis of the EA’s comments do not appear to reflectthis or recognise that the Council’s approach is based on risk avoidance rather thanmitigation.EA comment:The SFRA should provide information on the variation of risk within flood zones which areprotected by flood defence infrastructure, draw appropriate conclusions and makerecommendations for each potential development site”.• See mapping as this provides a comprehensive overview of depths and velocitiesacross the borough.• See Sequential Test Spread Sheet for site summary and recommendations.EA comment:Again we would refer the Council back paragraph 2.7 of the brief and the followingsections for the Level 2 SFRA requirements. Guidance on strategic flood riskassessment and management issues to be considered in policy development.We have identified open space areas that are potentially suitable for larger-scalemitigation. However, the Council’s decision process is inextricably linked to the PFRAand SWMP. Also the SFRA is based on avoiding higher risk areas and a fundamentalassertion that flood risk will be mitigated on site.We are presuming that beyond the River Douglas FAS, no further capital schemes arecurrently proposed for Wigan.2009s0578-S-L007-1.doc 4/710 December 2010www.jbaconsulting.co.uk
EA comment:Guidance on the preparation of FRAs for sites of varying risk across the flood zones.Consultants should provide spatial recommendations that go beyond the generalguidance in PPS25 to inform the preparation of FRAs.It is not for the SFRA to rewrite EA guidance on FRAs or the PPS. FRA’s need to be sitespecific and should only be prepared by suitably qualified individuals or organisations.In addition, it is not for the SFRA to stipulate requirements for an FRA, each one must beprepared to address the site specific constraints and impact of development proposals.Requirements for the FRA will also depend on available information and take account ofimprove understanding of flood risk over the next five years or so.As a result the SFRA requires prospective developers to consult with the EA and theCouncil at an early stage in the development planning process so that current issues areaddressed and to ensure an FRA addresses specific concerns for a siteEA comment:Recommended development approach and potential end use.The end use for each site is predefined by the Council and we have included anddiscussed the suitability of your development aspirations in terms of the PPS.Following our discussions we have deleted all sites that were deemed unnecessary andunsuitable in terms of flood risk. Those sites that remain in higher risk areas, have beenretained by the Council as key areas of regeneration. In these instances, we haveincluded recommendations for suitable land uses including open space and watercompatible purposes. These sites are still subject to Sequential Testing by the Council.EA comment:Proposed development control and technical issues to be resolved to permitdevelopment.The emphasis of the SFRA is risk avoidance. It is not about finding ways to “permit”development. The SFRA makes clear that flooding must be managed and fully mitigatedfor. The simplest way of doing this is to avoid development in high risk areas.Whilst we have set out the Council’s overarching principles for development in the SFRAit is not our intention (nor is it the purpose of the SFRA) to be overly prescriptive andimpose potentially unsuitable design constraints on developers. The technical issues canonly be resolved through detailed assessment, effective design, careful planning andtimely discussion with the EA and Council.EA comment:Mitigation options required to permit development.This will depend on the detailed design and cannot be prejudged at a strategic level.However, consideration of mitigations measures (and requirements for full floodwatermitigation on site, safe design, and opportunities for strategic mitigation) is included in theSFRA.2009s0578-S-L007-1.doc 5/710 December 2010www.jbaconsulting.co.uk
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Wigan Borough Hybrid SFRAVolume I:
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JBA OfficeJBA ConsultingSouth BarnB
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AcknowledgmentsJBA would like to ac
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Understanding flood risk from a pla
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8.3 Planning considerations........
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AbbreviationsABDAreas Benefiting fr
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The key objectives of a SFRA are to
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2 Flooding from RiversA detailed as
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1. Astely Brook2. Bedford Brook3. W
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Unique ID Watercourse Description L
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2.7 Understanding flood risk from a
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For example, flooding may affect ke
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3 Flooding from CanalsThe SFRA has
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3.2.2 Canal breach methodologyCanal
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4 Flooding from ReservoirsFollowing
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direction in Future Water3, Making
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oundaries. Nine key CDAs have been
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CDA Sites Site TypeLark Hill, Astle
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particular hotspots where surface w
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important role to play in reducing
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In the reverse situation, where flo
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8 Summary of riskA summary of flood
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Having followed this procedure it i
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9 Outline Mitigation OptionsChapter
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Water-resistant materials for floor
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JBA Consulting - Engineers Scientis
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JBA Consulting - Engineers Scientis
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Table B-1: Flood Risk Balance Sheet
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Map Name Map Reference Map Title De
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Page 65 and 66: Map Name Map Reference Map Title De
Page 81 and 82: D . Wigan Council - Data RegisterXX
Page 83 and 84: E . SUDs SuitabilityNew SiteReferen
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Page 111 and 112: of the extent of any works required
Page 113 and 114: Planning & Transport StrategyWigan
Page 115: Again, avoiding generalities, we ha
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Page 121 and 122: RECORD OF MEETINGStatus:JBA Project
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Level 2 Strategic Flood Risk Assessment (.pdf ... - Wigan Council

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