Reservoir Flooding

There are approximately 2100 reservoirs which each retain over 25,000 cubic metres (approx 5 million gallons) above natural ground level in England and Wales.

Any reservoir (above ground level) that contains over 25,000 cubic metres falls under the Reservoirs Act 1975. The Act ensures that the owners of a reservoir carry out necessary inspections and regular maintenance. Reservoir flooding could be very different from other forms of flooding. It could happen with little or no warning and you may need to evacuate immediately.

Reservoir flooding may be similar to river or surface water flooding if water escapes slowly, but in the unlikely event there is a catastrophic failure of the dam wall then a large volume of water could escape at once. Reservoir owners or operators will have on-site emergency plans in place if flooding was to happen.

Across the country, the likelihood of individual dam failure is very low. There hasn’t been a dam failure causing loss of life since the 1920’s. However, dam failures and flooding have occurred more recently than this.

If you know your property is in an area that could flood, buy protection equipment and prepare your property well in advance to reduce the risk of flood water getting inside. Remove flood protection equipment once the water has gone to help dry out your property.

Call the Natural Reources Wales Incident Hotline on 0800 80 70 60 if you discover an apparent fault at a reservoir.

Keep yourself Safe

  • Keep yourself and others clear of danger. Move away from the reservoir, keeping to higher ground, if you can do so safely.
  • Make sure 999 has been called if people are injured or if there is a threat to life.
  • Don’t walk or drive through floodwater.
  • Follow the advice of emergency services in the area.
  • Try to remain calm, think before acting and try to reassure others.

If you are worried about the risk of reservoir flooding, visit the Environment Agency website where you will find their risk of reservoir flooding map.