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

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Other CommentsBarley Brook modelling is now complete and we have new flood outlines available.These will not be published on our Flood Map because they represent an element ofsurface water risk and risk from surcharging urban drainage, however they may beuseful to incorporate within the SFRA. I would advise you to contact Ian Caunce in theFlood Risk Mapping team to discuss in further detail. (01772 714036).2) Wigan SFRA User GuideParagraph 4.7.1 Allowable discharge ratesReferring to bullet point 4 - acceptance of a free discharge in advance of the peak of theriver flood level seems an outdated approach to surface water management?Furthermore this doesn't appear consistent with current best practice/flood risk policyand if applied across a catchment (on a cumulative basis) could lead to an increasedflood risk (by shortening and increasing the peak on the catchment hydrograph). Wewould suggest that this bullet point is omitted to the document.Flood Warning Codes (Page VIII)The Flood Warning Codes have been revised by the Environment Agency. As such thedescription of the flood warning system will need to be updated.3) Flood Mapping Set A - Flood Zone MapsIt is difficult to determine the extent of functional floodplain to that of flood zone 3A asthe map key indicates a similar shading of blue. We would recommend that thefunctional floodplain layer is strengthened on the maps provided.I trust that you will find these comments useful, should you wish to discuss anything infurther detail please do not hesitate to get in touch.Yours faithfullyHelen TelferPlanning Liaison OfficerDirect dial 01925 543363Direct fax 01925 852260Direct e-mail helen.telfer@environment-agency.gov.ukCC: Rosalind Whitham, JBA – Via EmailEnd 3
Planning LiaisonEnvironment Agency - North West RegionAppleton House430 Birchwood BoulevardBirchwoodWARRINGTONWA3 7WDFor the attention of Helen TelferOur Ref: RW\2009s0578-S-L005-1.doc19 November 2010Dear Sirs,Wigan Borough Level 2 SFRAThank you for your comments received by email on 15 th November 2010 with regards tothe Wigan Borough Council SFRA. We have included our response, on behalf of theCouncil, addressing each of your points below using the same subheadings as used inyour letter reference SO/2006/000257/SF-01/IS1-L01 dated 11 November 2010.1) Level 2 SFRA ReportDevelopment behind Defences• Current Condition of Flood DefencesUnfortunately, the NFCDD data received for this study does not contain condition ratingsfor flood defences in Wigan. Therefore an existing condition assessment of flood defenceinfrastructure has not been undertaken for this SFRA.• Likely Future Flood Management PolicyFuture maintenance of flood defences and assets should follow the policy as set down inthe relevant Environment Agency flood risk management strategy. Information may alsobe available from the Catchment Flood Management Plan.• Probability and Consequence of Defence Overtopping and FailureThe design standard of the 42 raised defences within the Wigan Borough is typically 40 to50 years (6 have a 40 year design standard. The remaining 36 have a 50 year designstandard). During the 1% AEP design flood event, these formal defences will thereforeonly provide limited protection and are therefore likely to be overtopped or flood frombank level exceedance elsewhere in the catchment. Under the climate change scenario(i.e. 1% AEP flood event + 20% peak flow) more extensive flooding would be expected tooccur.During the 1% AEP design flood event all the defences within Wigan are therefore likelyto be overwhelmed. Using undefended modelling scenarios (as used in this SFRA) willmost accurately represent the extent of flood risk within Wigan and specific breachmodelling would not improve understanding.
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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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Page 55 and 56: Table B-1: Flood Risk Balance Sheet
Page 57 and 58: 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 91 and 92: New SiteReferenceWig 716Wig 706BSit
Page 97 and 98: Site Reference Site Location Soil T
Page 99 and 100: F . Flood Zone 3 Proposed Developme
Page 101 and 102: G . Environment Agency comments on
Page 103: Flood Hazard MappingThe Level 2 rep
Page 107 and 108: Guide makes further summation diffi
Page 109 and 110: Wigan Metropolitan Borough CouncilC
Page 111 and 112: of the extent of any works required
Page 113 and 114: Planning & Transport StrategyWigan
Page 115 and 116: Again, avoiding generalities, we ha
Page 117 and 118: EA comment:Guidance on the preparat
Page 119 and 120: Please give me a call to discuss wh
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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