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

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The Level 2 SFRA is structured as follows:1. Introduction.2. Flooding from rivers. Provides an assessment of the risk at key development sitesalong the River Douglas, Calico Brooks and Wigan Brooks3. Flooding from canals. Provides an assessment of areas that could potentially beaffected by overtopping or breach from the Leeds Liverpool Canal and BridgewaterCanal.4. Flooding from reservoirs. Due to implications for national security, the flood riskassociated with reservoir failure has not been considered in the Level 2 SFRA.5. Flooding from surface water and sewers. Contains a detailed assessment of floodrisk from surface water, which provides an indication of areas that may be affected bysewer flooding if the network were to surcharge. This chapter also introduces CriticalDrainage Areas and provides recommendations for Surface Water ManagementPlans.6. Cumulative impacts. Provides an understanding of the impact that developmentcould have on flood risk both within Wigan and downstream.7. Hydraulic interactions. Understanding the potential interactions between differentsources of flood risk in Wigan is critical. These have been mapped and tabulated inthe Level 2 SFRA.8. Summary of flood risk. The risk of flooding from all sources has been summarisedfor key communities.9. Outline Mitigation Strategy. This provides advice on how development couldproceed in flood risk areas and be compliant with the requirements of PPS25.1.4 Sequential Test spreadsheet and associated mappingThis SFRA includes the Sequential Test spreadsheet for all sites identified by the Council asbeing potentially suitable for future development in accordance with their perceiveddevelopment needs. The Council has, as part of the SFRA process, already rejected sitesthat are unsuitable based on significant flooding issues. In addition to the report, particularfocus need to be given to the Sequential Test spreadsheet, included as Appendix A and theassociated mapping in Appendix C.2009s0578 Final SFRA with Environment Agency Comments - L2 Ver5 Wigan.doc 7
2 Flooding from RiversA detailed assessment of fluvial flood risk has been undertaken throughout the borough toascertain areas of high flood risk and where there is a focus for future development. Thishas been undertaken using the 2D modelling package JFLOW.2.1 IntroductionThe Wigan Level 2 SFRA presents the risk of flooding from watercourses across the borough.It focuses on those areas at greatest risk, where strategic development sites have beenproposed by the Council. The river modelling that has been developed for the SFRA is of astrategic nature. Detailed studies should seek to refine the understanding of flood risk fromall sources where a specific site risk assessment is being prepared.An assessment of the depth and hazards associated with flooding from rivers, includingconsideration of residual risk behind flood defences has been undertaken where there is aknown risk of flooding and where there is a pressure for future development. Within theborough the majority of this development is contained within the existing urban areas.Potential developments within the borough can be split into two classifications; EmploymentLand Allocation (ELA) and Strategic Housing Land Availability Assessments. These are listedin Appendix A of this report.To help determine the extent and severity of flood risk a number of linked 1D (river) and 2D(floodplain) models have been assessed in order to determine the risk to future development.River modelling, developed for this SFRA, is strategic in nature.2009s0578 Final SFRA with Environment Agency Comments - L2 Ver5 Wigan.doc 8
Page 1 and 2: Wigan Borough Hybrid SFRAVolume I:
Page 3 and 4: JBA OfficeJBA ConsultingSouth BarnB
Page 5 and 6: AcknowledgmentsJBA would like to ac
Page 7 and 8: Understanding flood risk from a pla
Page 9 and 10: 8.3 Planning considerations........
Page 11 and 12: AbbreviationsABDAreas Benefiting fr
Page 13: The key objectives of a SFRA are to
Page 17 and 18: 1. Astely Brook2. Bedford Brook3. W
Page 19 and 20: Unique ID Watercourse Description L
Page 21 and 22: 2.7 Understanding flood risk from a
Page 23 and 24: For example, flooding may affect ke
Page 25 and 26: 3 Flooding from CanalsThe SFRA has
Page 27 and 28: 3.2.2 Canal breach methodologyCanal
Page 29 and 30: 4 Flooding from ReservoirsFollowing
Page 31 and 32: direction in Future Water3, Making
Page 33 and 34: oundaries. Nine key CDAs have been
Page 35 and 36: CDA Sites Site TypeLark Hill, Astle
Page 37 and 38: particular hotspots where surface w
Page 39 and 40: important role to play in reducing
Page 41 and 42: In the reverse situation, where flo
Page 43 and 44: 8 Summary of riskA summary of flood
Page 45 and 46: Having followed this procedure it i
Page 47 and 48: 9 Outline Mitigation OptionsChapter
Page 49 and 50: Water-resistant materials for floor
Page 51 and 52: JBA Consulting - Engineers Scientis
Page 53 and 54: JBA Consulting - Engineers Scientis
Page 55 and 56: Table B-1: Flood Risk Balance Sheet
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Map Name Map Reference Map Title De
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D . Wigan Council - Data RegisterXX
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E . SUDs SuitabilityNew SiteReferen
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New SiteReferenceWig 354Site Addres
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New SiteReferenceWig 855Wig 857Wig
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New SiteReferenceWig 716Wig 706BSit
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Site Reference Site Location Soil T
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F . Flood Zone 3 Proposed Developme
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G . Environment Agency comments on
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Flood Hazard MappingThe Level 2 rep
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Planning LiaisonEnvironment Agency
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Guide makes further summation diffi
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Wigan Metropolitan Borough CouncilC
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of the extent of any works required
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Planning & Transport StrategyWigan
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Again, avoiding generalities, we ha
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EA comment:Guidance on the preparat
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Please give me a call to discuss wh
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RECORD OF MEETINGStatus:JBA Project
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