Guidance

Example flood investigation criteria

Published 16 April 2025

Applies to England

© Crown copyright 2025

This publication is licensed under the terms of the Open Government Licence v3.0 except where otherwise stated. To view this licence, visit nationalarchives.gov.uk/doc/open-government-licence/version/3 or write to the Information Policy Team, The National Archives, Kew, London TW9 4DU, or email: psi@nationalarchives.gov.uk.

Where we have identified any third party copyright information you will need to obtain permission from the copyright holders concerned.

This publication is available at https://www.gov.uk/government/publications/investigating-a-flood-guidance-for-lead-local-flood-authorities/example-flood-investigation-criteria

As a lead local flood authority (LLFA), you can use flood investigation criteria to help you decide whether to investigate a flood.

The following examples are based on existing criteria of different LLFAs. You can use them to help create flood investigation criteria that are appropriate for your local area.

Property

You should conduct a flood investigation if there are:

  • 5 or more residential properties flooded within a specified area, settlement or catchment
  • 2 or more commercial properties flooded within a specified area, settlement or catchment
  • fewer than 5 residential or 2 commercial properties flooded where flooding lasts longer than one week
  • fewer than 5 residential or 2 commercial properties flooded on 2 or more occasions within 2 years

Infrastructure, agriculture and environment

You should conduct a flood investigation if there is:

  • flooding of any critical infrastructure or local services – including hospitals, health centres, clinics, surgeries, colleges, schools, day nurseries, nursing homes, emergency services and utilities sites
  • flooding to category 1 highways (motorways) or major rail links or railway stations for 2 hours or more
  • flooding to category 2 and 3a highways and other railway links for 4 hours or more
  • flooding to category 3b and 4 highways for 10 hours or more
  • flooding of more than 1 hectare of agricultural land of grade 3a and above
  • flooding of a designated environmental or heritage site

People

You should conduct a flood investigation if the observed flood depths and velocities caused ‘danger for most’ or ‘danger for all’ under the flood risk to people guidance.

Back to top