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Reservoir Emergencies

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While the chance of flooding from reservoirs is very small, understanding where water could go could help you stay safe. Reservoirs in the UK have an extremely good safety record with no incidents resulting in the loss of life since 1925. Carefully planned maintenance means flooding is  very unlikely to happen because reservoirs are regularly inspected and essential safety work is carried out. Local authorities are responsible for coordinating emergency plans for reservoir flooding and ensuring communities are well prepared. Even though reservoir flood plans are still in development local authorities already have general emergency response plans that can be used to respond to any emergency.

1. What is a reservoir?

A reservoir is usually an artificial lake where water is kept for use. Some reservoirs supply water for household and industrial use, others serve other purposes, for example, as fishing lakes or leisure facilities.

The work currently being done on planning for reservoir emergencies involves large raised reservoirs that can hold at least 25,000 cubic metres (approximately 5 million gallons) of water above natural ground level. There are over 2,000 of these in England and Wales.

2. What is a reservoir emergency?

Usually this means a problem has been identified with the reservoir, so the water level has to be lowered to reduce the risk of reservoir failure and to enable repairs to be carried out.

3. What does reservoir failure mean?

All reservoirs are inspected regularly to ensure that if there are early signs of a problem then these are spotted and dealt with long before the reservoir or dam can fail. If a reservoir does fail it will no longer be able to safely hold water and will need to be emptied.

4. Why is this different from other types of flooding?

It could have exactly the same effect as other types of flooding, and cause a slow increase in the level of water. However, if a reservoir dam were to suddenly fail, a large volume of water could escape at once. It is important that plans are prepared to deal with this “worst case” scenario, so that anyone who might be affected by the flooding knows what action to take.

5. How will I know if my property might be affected by reservoir/ dam failure flooding?

Information about reservoir flooding in England and Wales is available from a

number of sources. Reservoir flood maps are available on the Environment Agency’s website where you can enter a postcode and find out if you live or work in an area that could be affected by reservoir flooding. You can find a link to the reservoir flood maps and further information at:

You may also hear directly from your local authority that you are at risk of reservoir flooding. Local authorities are initially preparing emergency plans for the 100 higher priority reservoirs in England and Wales *. As part of the plan, they will be contacting households that may be most affected.

6. I don’t live near a reservoir. Why do I need to be prepared for reservoir flooding?

Although people closest to a reservoir are most likely to be most affected if a

reservoir failed, the extent of the flooding from a reservoir can extend 50 miles or more from the reservoir itself. Also, local geography such as valleys could channel the water and make flooding worse in areas at some distance from the reservoir.

7. How safe are reservoirs/dams?

In the UK, there has been no loss of life as a result of reservoir flooding since 1925. Across the country as a whole, the likelihood of a complete reservoir failure is very low and the likelihood of flooding from a reservoir is far lower than from other forms of flooding.

Before 1925, when reservoirs were not as well maintained as they are today, there were a number of extreme failures which led to the introduction and updating of reservoir safety legislation in 1930, 1975, 2003 and 2010. No lives have been lost as a result of reservoir flooding since the introduction of this safety legislation.

8. Does anybody check reservoirs for signs of problems?

At present all large reservoirs (above 25,000 cubic metres in capacity) must be inspected and supervised by panel engineers, a group of specialist civil engineers appointed under the Reservoirs Act 1975. The Panel comprises:

  • ‘Construction engineers’ appointed to supervise the design and construction of a new reservoir or significant changes to a reservoir.
  •  ‘Inspecting engineers’ appointed to inspect reservoirs, and to identify any actions that might need to be taken in the interests of safety when appropriate. They can also certify that works recommended in the interest of safety have been carried out to suitable standards before the due date.
  • ‘Supervising engineers’ appointed to supervise the operation and maintenance of a reservoir at all times once the construction of the reservoir is complete. More information on reservoir engineers is available at:

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