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Flooding from reservoirs

The shading on the map shows the worst-case scenario for the area that could be flooded if a large reservoir were to fail and release the water it holds. A large reservoir is one that holds over 10,000 cubic metres of water, equivalent to approximately 4 Olympic sized swimming pools.

Reservoir flooding is extremely unlikely to happen. There has been no loss of life in the UK from reservoir flooding since 1925. All large reservoirs must be inspected and supervised by reservoir panel engineers. As the enforcement authority for the Reservoirs Act 1975 in Wales, we ensure that reservoirs are inspected regularly and essential safety work is carried out.

The reservoir flood maps do not indicate any likelihood of a flood occurring.

What to do if a reservoir failed

In the unlikely event that a reservoir dam failed, a large volume of water could escape at once and flooding could happen with little or no warning.

If you live or work in an area that could be affected by flooding from a reservoir, you should plan in advance what you would do in an emergency. You may need to evacuate immediately. Consider and plan where, and how, you would go to safety, and be ready to follow the advice of emergency services.

To find out about local emergency plans, contact your local authority. Be aware that they may not be able to give you any specific information immediately as developing reservoir emergency plans is a new responsibility.

This area may also be at risk from other types of flooding.

To learn more about how reservoirs are kept safe, please see our pages on Reservoir Safety.

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