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

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