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

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ContentsContents .......................................................................................................................... 1Abbreviations .................................................................................................................. 41Introduction ........................................................................................................ 51.1 Background .......................................................................................................... 51.2 General scope and objectives of SFRAs ............................................................. 51.3 Level 2 SFRA scope and objectives .................................................................... 61.4 Sequential Test spreadsheet and associated mapping ....................................... 72Flooding from Rivers ......................................................................................... 82.1 Introduction .......................................................................................................... 82.2 Terminology - Flood Zone Definitions .................................................................. 92.3 Flood Defences .................................................................................................... 92.4 Areas Benefiting from Defences .......................................................................... 132.5 Douglas CFMP Account of Historical Flooding ................................................... 132.6 Defended Flood Zone 3 areas ............................................................................. 132.7 Understanding flood risk from a planning perspective ........................................ 142.8 Methodology and Assumptions ........................................................................... 152.9 River modelling scenarios.................................................................................... 152.10 Model outputs ...................................................................................................... 152.11 Flood Hazard Zones ............................................................................................ 162.12 River Douglas Flood Alleviation Scheme ............................................................ 173Flooding from Canals ........................................................................................ 183.1 Introduction .......................................................................................................... 183.2 Flood risk from canals .......................................................................................... 184Flooding from Reservoirs ................................................................................. 224.1 Reservoir locations .............................................................................................. 225Flooding from Surface Water and Sewers ...................................................... 235.1 Introduction .......................................................................................................... 235.2 Green Infrastructure ............................................................................................. 235.3 Surface Water and SUDs Suitability .................................................................... 235.4 Surface Water and Sewer Capacity Mapping...................................................... 245.5 Recommendations for Surface Water Management ........................................... 295.6 Taking Surface Water Management Plans forward ............................................. 306Cumulative impacts of future development and drainage design ............... 316.1 Introduction .......................................................................................................... 316.2 Development Drainage Impacts .......................................................................... 316.3 Considering downstream impacts ....................................................................... 316.4 Wider impacts ...................................................................................................... 317Hydraulic linkages ............................................................................................. 337.1 Introduction .......................................................................................................... 337.2 Canal and river interactions ................................................................................. 337.3 Hydraulic interactions resulting from reservoir breach ........................................ 357.4 Hydraulic interactions affecting surface water ..................................................... 357.5 Hydraulic interactions affecting the sewer network ............................................. 358Summary of risk ................................................................................................. 368.2 Sustainability Appraisal........................................................................................ 372009s0578 Final SFRA with Environment Agency Comments - L2 Ver5 Wigan.doc
8.3 Planning considerations....................................................................................... 378.4 Development sites benefitting from defences ..................................................... 389Outline Mitigation Options ................................................................................ 409.1 Introduction .......................................................................................................... 409.2 Planning considerations....................................................................................... 409.3 Summary ............................................................................................................. 42A .B .C .D .E .F .G .Wigan Council - Sequential Test ...................................................................... IWigan Council - Flood Risk Balance Spreadsheet ........................................ IIWigan Borough Council - SFRA Maps ............................................................ VWigan Council - Data Register ......................................................................... XXXISUDs Suitability ................................................................................................. XXXIIFlood Zone 3 Proposed Development Site Analysis ..................................... XLVIIIEnvironment Agency comments on Wigan SFRA with responses fromJBA ...................................................................................................................... XLIXList of FiguresFigure 3-1: Sample Breach Hydrograph ....................................................................... 20List of TablesTable 2-1: NFCDD Defence Assets in the Wigan Borough ......................................... 11Table 2-2: Summary of Flood Risk to Development Sites in Flood Zone 3 .............. 14Table 2-3: River Modelling Scenarios ........................................................................... 15Table 2-4: Debris Factors for Flood Depths, Velocities and Dominant LandUses .................................................................................................................... 16Table 2-5: Scales of Flood Hazard ................................................................................ 17Table 4-1: Key Reservoirs .............................................................................................. 22Table 5-1: Critical Drainage Areas & Associated Development Sites ....................... 26Table 7-1: Canal River Interactions ............................................................................... 34Table 8-1: Environmental Land Allocation Sites ......................................................... 38Table 8-2: Areas Benefiting from Defences ................................................................. 38Table B-1: Flood Risk Balance Sheet ........................................................................... IIITable E-1: Proposed SHLAA Development Site SUDs Suitability ............................. XXXIITable E-2: Proposed ELA Development Site SUDs Suitability .................................. XLIV2009s0578 Final SFRA with Environment Agency Comments - L2 Ver5 Wigan.doc
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: Understanding flood risk from a pla
Page 11 and 12: AbbreviationsABDAreas Benefiting fr
Page 13 and 14: The key objectives of a SFRA are to
Page 15 and 16: 2 Flooding from RiversA detailed as
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
Page 57 and 58: Map Name Map Reference Map Title De
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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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