Flood risk assessment

A flood risk assessment is required if your development meets the following criteria:

  • is a size of one hectare or over in flood zone 1
  • is within flood zone 1 which has critical drainage problems as notified by the Environment Agency (none currently notified in North Somerset)
  • is in flood zones 2 and 3
  • could be affected by sources of flooding other than rivers and the sea (for example surface water, reservoirs, groundwater), where its development would introduce a more vulnerable use
  • where there is an increased risk of flooding, from any source, in the future (as identified within the strategic flood risk assessment).


The assessment should look at the flood risk to properties and people, and show how it will be managed. It will need to 

  • show any opportunities to reduce flooding
  • show any use of sustainable drainage systems
  • address any requirement for safe access to and from a development in a flood risk area

The level of detail in your flood risk assessment will depend on the level of flood risk at your site. More detailed assessments will include hydraulic modelling. Flood risk is worked out by considering:

  • the type of development
  • the size of site and its location in relation to flood zones
  • the amount of surface water runoff the site will discharge
  • other sources of flooding (e.g. groundwater)

Completing a flood risk assessment does not mean a development is acceptable in terms of flood risk.

You may wish to check your assessment against the Environment Agency's Flood Risk Standing Advice before you submit it to us. 

More information

For more information on the policies around flood risk and assessments, please see the following: