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

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