Guidance

Flash flooding

The dangers of flash flooding and how to stay safe.

From:
Environment Agency
Published
11 November 2013
Last updated
20 September 2023 — See all updates

Applies to England

Flash flooding is very dangerous. Do not walk or drive through the water. Move to higher ground or the upper floor of a building if it is safe. Call 999 if you need emergency help.

Flash flooding is a very dangerous type of flooding. It happens when a lot of heavy rain falls in a short period of time:

  • onto the ground
  • into a river or stream

This can create deep, fast-moving water that can injure or kill people and damage buildings.

Flash flooding can happen anywhere, in towns, cities and the countryside. It can also happen a long way from rivers, lakes and the sea. It can take different forms. Some examples include:

  • a river overflowing because of heavy rain
  • water pooling very quickly in an underpass in a town or city
  • water rushing down a hill because of a reservoir failure

Flooding caused by lots of rain collecting on the ground is also called surface water flooding.

Check the risk

Flash flooding is difficult to predict. It can happen anywhere, even in areas that have not flooded before or not flooded for a long time.

You can check if you are at risk from flooding, including surface water flooding, and take steps to prepare:

Areas at higher risk

There are natural and human-made features that can put an area at higher risk of flash flooding, including:

  • rivers that are narrow and steep
  • small rivers in towns and cities with lots of buildings and pavements
  • steep-sided valleys
  • soil that cannot absorb water easily, like clay and rock
  • areas with few trees or vegetation
  • areas of intensive agriculture
  • areas that contain mines
  • human-made alterations to rivers and streams, like channels

You may be more at risk if you live or are staying in a:

  • basement
  • boat
  • building with one floor (storey)
  • bungalow
  • caravan
  • mobile home
  • tent
  • wooden structure

If you own a camping or caravan site, find out about managing the risk of flooding.

Know the signs

Flash flooding can happen suddenly with no warning. Some of the signs include:

  • very heavy rain, often from thunderstorms
  • severe weather reports and warnings
  • rising water levels
  • dark water that is moving with great force
  • debris in rivers and streams
  • damage to buildings from flood water

Staying safe

You should avoid an area that is experiencing flash flooding.

Flash flooding can be very unexpected. You may need to act:

  • quickly
  • before a warning is given
  • before the emergency services get to you

To make yourself safer during flash flooding:

  • if it is safe, move to higher ground or the upper floor (storey) of a building
  • do not walk or drive through the flood water
  • do what the emergency services tell you
  • call 999 if you are trapped or need emergency help

Shallow flood water (around 15cm or 6 inches) that does not look dangerous can knock a person over or conceal hazards. It only takes around 60cm (2 feet) of water to carry away a vehicle of any size.

Do not use flimsy or temporary structures – like a tent or a caravan – for shelter during flash flooding.

Find out more about what to do during a flood.

Get information during flash flooding

During flash flooding, you can get information from:

You can contact the emergency services by phoning 999 if you are in immediate danger.

How it can affect you

Flash flooding is very dangerous and disruptive because:

  • there can be a lot of powerful, fast-flowing water
  • the water can injure and kill people
  • it can happen suddenly
  • there may not be any warning
  • the water can carry away cars and other vehicles
  • the water can damage or destroy buildings

Recovering from flash flooding

How long flash flooding lasts will depend on the location. Recovery from flash flooding can take a long time, depending on the damage.

Read how to recover after a flood.

Get more help and information from Floodline

You can contact Floodline for advice:

Floodline
Telephone: 0345 988 1188
Textphone: 0345 602 6340
24-hour service Find out about call charges

Updates to this page

Published 11 November 2013
Last updated 20 September 2023 + show all updates

  1. Removed PDF and added relevant information to the page.

  2. First published.

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