Environmental Statement volume 4 - Chiltern Evergreen3

It is proposed that the current proposal is most appropriate according to:Maintaining access for the public right of way with minimal impact on users; andSafety of users.It is proposed that there are no reasonably alternative sites, given the requirement for arailway crossing in the immediate area to compensate for the closure of the pedestrianlevel crossing.The Exception Test must be satisfied, as the development is in Flood Zone 3.The site is on not on previously-developed land. It is demonstrated above thatthere are no reasonably alternative sites on previously-developed land.A Level 3 FRA is required to demonstrate that the development will neitherobstruct flood flows across the floodplain nor consume floodplain storage; if notthen this work must quantify the mitigation required.The footbridge lies on a flat area of land, adjacent to a small dry island. The probabilityof a significant obstruction to flood flows is low.A commitment has been made by the project that appropriate mitigation will be providedfor demonstrable loss of floodplain storage and obstruction to flood flows, in agreementwith the Environment Agency.A further commitment is provided that the drainage ditch running adjacent to the railwaywill not be affected by the development. Similarly, it is understood that the culvert tothe northeast of the site will not be changed by the development.The bridge will utilise standard design for drainage of the span. The development liesadjacent to a drainage network and hence SUDS of suitable type will be provided toattenuate runoff from the bridge drainage, particularly for short return period rainfall.3.5.7 AP12 – Millstream and Cherwell ViaductsThe development sites lies within Flood Zone 3, and the Sequential Test has thereforebeen applied. There are no reasonably available sites for this particular developmentelsewhere, given that the viaducts exist at this site as the watercourses and railwayintersect here.The Exception Test must be satisfied, as the development is in Flood Zone 3.The site is on previously-developed land. The land has an existing use as railwayinfrastructure.Given that the bridge footings, wing walls and pier abutments are not beingchanged, it can be determined that the structure will not obstruct flood flowsacross the floodplain nor consume floodplain storage over and above the impactof the existing structure. A commitment is given that these works are indeed redeckingonly.As the bridge sub-structure is not being altered, soffit levels will be dictated by thecurrent design. This is discussed further within Section 3.6.A surface water runoff calculation for this site has not been provided for thisdevelopment site as it is directly over a watercourse, as discussed in Section 4.33