flood map challenges and reclassification

Flood Risk

Flood Map Challenge

 

In 2004 national flood maps were created by the Environment Agency to support the planning documents PPS 25 and TAN15. The maps published are based on Digital Terrain Modelling (DTM).

The flood maps give a general picture and are not site specific. Structures such as bridges and embankments, which may affect the flood plain locally, have not generally been taken into account in producing the flood maps.
The EA will consider challenges to the maps submitted by Waterco and make amendments as appropriate. Waterco have successfully challenged the EA flood map in a number of locations with an example being Wepre Park, Connah’s Quay.

In order to change the Flood Zone outlines, revised flood extents must be produced by detailed site specific flood modelling and assessment, in accordance with EA guidance.

A flood map challenge would include the following:
 

  • Reviewing existing flood defences.

  • Agreeing with EA the extent and details of the model.

  • Relationship of site levels to potential flood levels (AOD).

  • Historical data research on past flooding incidents.

  • Obtaining data from the EA for river levels.

  • Extensive survey information for the hydraulic model.

  • Flood Modelling using MIKE FLOOD.

  • Breach Assessment and Overland Flow Assessment if required.

  • Calculating 1 in 100 and 1 in 1000 year flood levels and mapping their flood extents (zones).

Please do not hesitate to contact us if you have any questions regarding a Flood Map Challenge.