Reservoir Emergencies

Date published: 12 June 2019 14:17

Reservoirs are artificial lakes where water is kept either to supply water for domestic or industrial use or for recreational purposes. There are approximately 2100 reservoirs which 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. The Act ensures that the owners of the reservoir carry out necessary inspections and regular maintenance.

Across the country, the likelihood of individual dam failure is very low. However on extremely rare occasions problems have been identified with reservoirs that have required lowering of the depth of water to enable repairs to be carried out.

What are we doing?

We work together to look at a wide range of emergencies. Planning for the unlikely event of a Reservoir Emergency is no different. We are working together to ensure that all necessary procedures are in place, just in case we have to respond to an emergency at one of the reservoirs in our area. It is important that we develop these plans so that people know what to do if water starts to escape from these reservoirs.

Reservoir flooding may be similar to river or surface water flooding if water escapes slowly but if there is a catastrophic failure of the dam wall then a large volume of water could escape at once. Reservoirs with a volume of greater than 25,000 cubic metres are regularly inspected by a group of specialist civil engineers appointed under the Reservoirs Act 1975 and any identified safety works are immediately carried out. The Environment Agency as the regulator ensures that the inspections and any remedial works are carried out.

How do I find out more?

Following the floods of June 2007 Sir Michael Pitt produced a report which resulted in the Flood and Water Management Act 2010 so that there is now a requirement for planning for all types of flooding including reservoir inundation. As part of this process the UK Government has ensured the production of outline inundation maps of all reservoirs with a volume greater than 25000 cubic metres. Members of the public can now see whether they are at risk of reservoir flooding by viewing the Environment Agency website and the area called the 'What's In Your Backyard'which will allow you to view outline reservoir flood maps in the same way that flood maps for river and coastal flooding are available. You may also wish to visit their 'Am I at risk of flooding' webpage, which is specifically about flooding from reservoirs.

It is important to note the following:

There has been no loss of life from reservoir failure in the UK since the 1920s and we have robust legislation in place setting safety standards.
The maps have been prepared for emergency planning purposes and for this reason they reflect a credible worst case scenario - this means that if a reservoir failure did occur it would most likely be far less severe than the scenario shown in the maps.

We've mapped the credible worst case scenario so that emergency planners have all the information they might need to increase public safety.

  • Reservoirs have always posed a very small risk to nearby communities, as many communities are already aware. The level of risk has not increased.
  • The areas highlighted green on the reservoir flood maps are the areas that might be flooded in a credible worst case scenario. The maps do not give any information about the depth or speed of the flood waters or the length of time it would take for the flood waters to reach any location. Even in a worst case scenario many areas highlighted green would be expected to receive no more than one or two centimetres of flood water.
  • Provided reservoirs are properly maintained then the likelihood of reservoir flooding is much lower than other forms of flooding. Current reservoir regulation, which the Flood and Water Management Act 2010 further enhances, aims to ensure that all reservoirs that pose a safety risk are properly maintained and monitored in order to detect and repair any problems as early as possible.

Who should I call if I think I notice a problem with a reservoir?

Call the Environment Agency Incident Helpline on 0800 807060 if you discover an apparent fault at a reservoir.

How will I know if there is an emergency?

You will be alerted in one or more of the following ways:

  • Emergency services in your area may knock on your door or use a loudhailer system. You may be given an evacuation card which will give you specific advice about where you should go.
  • Helicopter Skyshout (public address system) warnings may be given.
  • Local television and radio news alerts.

You should always follow the advice of the emergency services.

What should I do if I find myself in the path of a reservoir in an emergency?

Although extremely unlikely, flooding from reservoirs could occur with little or no warning. You may need to react before emergency services can reach you. If you find yourself in the middle of a reservoir emergency, it is important to:

  • 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
  • Do not walk or drive through floodwater
  • Try to remain calm, think before acting, and try to reassure others.
  • Check for injuries - remembering to help yourself before attempting to help others.

    It is important to keep roads and other access routes clear for the emergency services and for the evacuation of people who are in the area expected to flood. If you are not affected by the reservoir flooding but are close to the potential flood zone you should:

  • Keep away from the reservoir
  • Stay away from any flooded area and low ground and get away from building that may collapse
  • Tune in to local radio or TV for more information

You should always follow the advice of the emergency services.

Where should we go if there is an emergency?

If you become aware that your property may soon be flooded and you have not received any earlier information, you should listen out for advice on the radio and television, and take directions from local officials. If you do not hear from officials but have good reason to believe you are in the flood zone of a reservoir that has a realistic chance of failing then you should follow the advice given above

What should I take with me?

You should prepare an emergency pack containing such as:

  • Personal documents (e.g. insurance policy)
  • Contact numbers for family, friends, doctor etc
  • Battery operated or wind-up radio
  • Mobile phone
  • Waterproof clothing
  • First aid kit
  • Blankets
  • Family medication
  • Items for your children and babies where appropriate
  • What provision could you make for the family pets?

If you needed to leave the house, do you know where you would go and how you would get there? Do you have friends or family who could provide you with accommodation? If you don't have anywhere to go, you will be able to stay in a Rest Centre set up by the Council.

Will it be safe to drive?

If emergency services are in the area, you should seek advice from them on the best way for you to evacuate the area. In some areas community transport may be provided. It is important to keep traffic flowing so that the emergency services have access to the reservoir and to people who need their assistance.

It is important not to underestimate the danger of floodwaters:

  • Do not walk through moving water. 15cm (six inches) of moving water can knock you off your feet. If you have to walk in water, walk where the water is not moving. Use a stick to check the firmness of the ground in front of you.
  • Do not drive through floodwaters. It only takes 60cm (two feet) of water to lift and sweep away a 4x4 car or small lorry.
  • There may be hidden dangers in the water including rubble, vegetation and exposed drains.

How will I know which way to go?

You should follow instructions from the local emergency services. If there are no emergency services in the area, and if it is safe to do so, you should move away from the reservoir, keeping to higher ground. You should do this as soon as possible.

Do not approach the flood water.

Will it be safe to shelter inside buildings?

No, not if you have been told to evacuate. If you are told to evacuate your property because it is in the path of the flood, you should leave your house as soon as possible. If emergency services are in the area but they have not told you to evacuate you should await further information: tune into local radio or television stations and follow the advice of emergency services or other officials in the area.


It is important that you do not return to your property until you are advised it is safe to do so. For your own safety you need to be sure that gas and electricity and drinking water supplies are safe and that your home is structurally sound. This may take some time.

Financial Issues

Since the risk from reservoir flooding is very low, the Association of British Insurers have indicated that there should be no increase in insurance costs if you now find that your home is at risk from reservoir flooding. It is also unlikely that there will be any effects on property prices in the area.