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

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JBA state that “information may also be available from the Catchment FloodManagement Plan”. We would again refer the Council to the above paragraph (2.7 a)from the brief which expects the Level 2 Report to contain links / reference to therelevant parts of both the Douglas CFMP and Mersey Estuary CFMP. Probability and Consequence of Defence Overtopping and FailureWe note the assumption made by JBA in the assessment of breach modeling and thatthe defence within the borough are likely to be overwhelmed. Whilst it would have beenuseful to look at breach scenarios at lower return periods, we accept that the use of the1% AEP flood event + 20% peak flow is in line with paragraph 3.63 of the PracticeGuide and we would not want to pursue this issue further.We would agree with JBA and the assumed ‘undefended scenario’ for sequential testingof key regeneration sites.However it is also noted by JBA that all but key regeneration sites have been deleted inflood zone 3. PPS25 is clear in that where development can not be located outside ofhigh flood risk areas, the level 2 SFRA should provide further information to satisfy the‘Exception Test’. (See response to Flood Risk Guidance below). River Douglas Flood Alleviation SchemeWe are aware from discussions for a proposed development site within Wigan TownCentre, that the Council has already commissioned JBA to develop a breach model forthe defences on the River Douglas.The SFRA should consider the inclusion of this information or at the very least providefurther guidance for proposed developments in this area.Flood Hazard MappingComments on this have been noted and we have nothing further to add.Section 8: Summary of RiskComments on this are noted, however the SFRA wording should be amended in thissection so not to confuse readers of the document. (I.e. the report should not be incontradiction with PPS25).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,which are 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 appraisalCont/d.. 2
of the extent of any works required to provide or raise the flood defence to anappropriate standard.The SFRA should provide information on the variation of risk within flood zones whichare protected by flood defence infrastructure, draw appropriate conclusions andmake recommendations for each potential development site”.Again we would refer the Council back paragraph 2.7 of the brief and the followingsections for the Level 2 SFRA requirements:e. Guidance on strategic flood risk assessment and management issues tobe considered in policy development.f. Guidance on the preparation of FRAs for sites of varying risk across theflood zones. Consultants should provide spatial recommendations that gobeyond the general guidance in PPS25 to inform the preparation of FRAs,including:-i. Recommended development approach and potential end use,ii. Proposed development control and technical issues to be resolvedto permit development,iii. Mitigation options required to permit development,iv. Supplementary design guidance including minimum floor levels,access and egress, site layout recommendations in relation tovulnerability, building materials and flood resilient construction,v. Residual risk management,vii. Overall site-by-site summary guidance suitable for issuing topotential developers.i. Mitigation options, and potential delivery mechanisms should bepresented as part of the Level 2 SFRA.In light of this issue we would suggest that the level 2 SFRA has not met therequirements of PPS25 or the original brief.Design Standards for the River Douglas ABDComments are noted and the Council will need to make a decision on the inclusion ofthis data.Other CommentsComments are noted and the Council will need to make a decision on the inclusion ofthis data.2) Wigan SFRA User GuideParagraph 4.7.1 Allowable Discharge RatesWe understand from email correspondence that the Council agree with our previouscomments on this issue and that JBA have been advised to change the wording.Flood Warning CodesCont/d.. 3
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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 81 and 82: D . Wigan Council - Data RegisterXX
Page 83 and 84: E . SUDs SuitabilityNew SiteReferen
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Page 87 and 88: New SiteReferenceWig 855Wig 857Wig
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 and 104: Flood Hazard MappingThe Level 2 rep
Page 105 and 106: Planning LiaisonEnvironment Agency
Page 107 and 108: Guide makes further summation diffi
Page 109: Wigan Metropolitan Borough CouncilC
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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