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

More documents

Recommendations

Info

To maintain consistency with other SFRA’s and national guidance in PPS25, SequentialTesting has been based on undefended model scenarios. In the absence of detailedmodelling in some areas of Wigan (no model files and/or associated GIS were availablefor many watercourses south of the Douglas), strategic mapping was used to definehazard criteria and inform the sequential test.This approach, adopted by the Council, is therefore precautionary and all but keyregeneration sites (in FZ3) have been deleted during Sequential Testing. On this basis,the Council have been able to make the informed planning decisions presented in thisSFRA.• River Douglas Flood Alleviation SchemeAs you are aware, no modelling information for the River Douglas Flood AlleviationScheme was made available for this SFRA. We understand that design flows from theRiver Douglas will be restricted to the 20 year standard and that the EA intend to updatethe Flood Zone map to include the flood limiting effect of the Douglas scheme in duecourse.It is assumed that the Council will be provided with a copy of the updated Flood ZoneMap when it becomes available for them to take account of the changes in their mappingand make appropriate planning decisions at that time. It is also anticipated that the floodrisk to identified Wigan town centre development areas will be reduced on completion ofthe Douglas Flood Alleviation Scheme. However, it should also be noted that detailedsite specific Flood Risk Assessments will still be required to accompany developmentproposals in order to demonstrate safe and appropriate development.Flood Hazard MappingThe key on the mapping will be amended for continuity.Section 8: Summary of RiskTo clarify, the SFRA includes a review of Open Space Areas that are potentially suitable(in terms of proximity to watercourses) for large-scale strategic mitigation.However, in reality sites identified for potential development are located throughout theWigan area and strategic flood risk mitigation, beyond the Douglas Flood AlleviationScheme, is limited.To prevent potential development increasing flood risk, flood mitigation measuresinvariably need to be close to, or preferably within the proposed development boundary(particularly where level mitigation is required).Further strategic mitigation measures may best be located where benefit to both existingdevelopment and proposed development can be identified. In order to progress this, theSFRA includes well defined Critical Drainage Areas (CDAs), which are based on a wealthof historical flooding data provided by Wigan. This will need to form the basis of theCouncil’s SWMP and be linked back to the Open Space Areas.Flood Risk GuidanceAlthough we understand your comment suggesting a “flood risk summary” is produced,we believe the amount of information included in the SFRA and accompanying User2009s0578-S-L005-1.doc 2/419 November 2010www.jbaconsulting.co.uk
Guide makes further summation difficult as key aspects will invariably be omitted orexplained too simplistically.We have made the SFRA report as succinct as we can so that users may focus on thekey aspects of the assessment. The further detail and explanation is provided in theSFRA User Guide.Our aim is to encourage the user to read the appropriate sections of the report fully.Design Standards for the River Douglas ABDThis is a question for the Council. Presumably this update has already been releasedunder licence to Wigan Council but to date this has not been forwarded to JBA.Therefore, the GIS mapping can be easily be updated by the Council on the digitaldeliverables being provided by JBA with the SFRA. Unfortunately, if the Council alsowant to update the SFRA maps we would have to review the effort required and theremay be an additional cost to change them at this late stage due to the final mappingproducts already being agreed.Other CommentsHaving looked at the current Barley Brook Flood outlines, there are only 4 proposeddevelopment sites in this area.These are:• SHLAA site Wig 728• ELA site EM1 A24 d• ELA site EM1 A24 b• ELA site EM1 A24 aThese sites are currently located with in Flood Zone 1. Reference to a new EA model willbe included in the Sequential Test spreadsheet for these sites.As with our comment above, the GIS mapping can be easily be updated by the Councilon the digital deliverables being provided by JBA with the SFRA. Unfortunately, if theCouncil also want to update the SFRA maps we would have to review the effort requiredand there may be an additional cost to change them at this late stage due to the finalmapping products already being agreed.2) Wigan SFRA User GuideParagraph 4.7.1 Allowable discharge ratesWe believe the correct balance has been made here between ensuring sustainablemanagement of surface water and developing practical solutions for surface watermanagement particularly when existing urban development is under consideration.When the section is read in its entirety it provides a clear emphasis and requirement forsustainable management of surface water as part of development planning. This finalpoint actually focuses on the potential for discharge from development sites to passdownstream before the main peak flood event on the watercourse occurs. This is2009s0578-S-L005-1.doc 3/419 November 2010www.jbaconsulting.co.uk
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 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
Page 81 and 82: D . Wigan Council - Data RegisterXX
Page 83 and 84: E . SUDs SuitabilityNew SiteReferen
Page 85 and 86: New SiteReferenceWig 354Site Addres
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: Planning LiaisonEnvironment Agency
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
show all

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

You also want an ePaper? Increase the reach of your titles

Delete template?

Save as template?