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Flood risk assessment

What information should I supply in a flood risk assessment?

A flood risk assessment should identify and assess the risks of all forms of flooding to and from the development and demonstrate how these flood risks will be managed, taking climate change into account.

For major developments in Flood Zone 1, the FRA should identify opportunities to reduce the chances and results of flooding. The assessment should contain a sequential testing statement, where the applicant advises whether the development can be accommodated in other (sequentially preferable) zones of lower flood risk.

The flood risk assessment should identify the following:

Within flood zone 1: low probability

  • existing flood risk to the site from localised sources and impact of development upon run off rates
  • design measures proposed to mitigate run off rates (SUDS) 

Within zone 2: medium probability

  • existing flood risk to the site from all sources and potential impact of development upon flood risk only (High level assessment only)
  • design measures proposed to mitigate risk of flooding, and their impact (details should include floor levels, ground levels, evacuation routes, SUDS)

Within zone 3: high probability (and functional floodplain)

  • sequential test required for windfall sites
  • existing flood risk to the site from all sources (e.g. flood depth, flow routes, flood velocity, defence failure)
  • potential impact of development upon flood risk
  • design measures proposed to mitigate risk of flooding, and their impact (details should include floor levels, ground levels, evacuation routes, SUDS etc)

Note: applications for development in areas at risk of flooding which do not include a satisfactory FRA will not be treated as a valid planning application. 

When is a flood risk assessment required?

Planning applications for development proposals of 1 hectare or greater in flood zone 1 and all proposals for new development located in flood zones 2 and 3 should be accompanied by a Flood Risk Assessment (FRA).

Access to the flood maps is available to help you check if your application site falls within a flood zone.