Understand your reservoir risk designation

We must consider the flood consequence which may occur if your large, raised reservoir fails. This informs the standard of safety to be provided by you and the level of regulation required of us. We call this process designation.

We designate reservoirs to recognise that they pose differing levels of hazard. There are two categories:

  1. High-risk reservoirs are large, raised reservoirs which we designate as high-risk because we think human life could be endangered in the event the dam fails, causing an uncontrolled release of water. The subsequent flood could have the potential to threaten human life in homes, businesses, at work or leisure facilities, on road and rail networks and at other infrastructure downstream. High-risk reservoirs are subject to all the requirements of the Reservoirs Act 1975.
  2. Large, raised reservoir includes all reservoirs with a raised capacity of 10,000 cubic metres, or more, above natural ground level which have not been designated as high-risk reservoirs. The law does not define any reservoir as low risk, but we may refer to them as ‘lower risk’ or ‘not-high-risk’. If your reservoir is not designated, its failure could still result in damage to neighbouring property and the environment.

We use a three-step process to decide our designation:

  1. provisional designation
  2. consideration of any representation you make
  3. final designation

Provisional Designation

We are required to make a designation based on the assumption that a reservoir or dam has failed. This means we do not consider the likelihood of the dam failing. Our focus is on flood consequence and not flood risk.

Our first review considers the consequences a flood might have on the people living and working downstream based on the information we have about your reservoir which normally includes:

  • flood maps showing the flooding which may occur if the reservoir dam fails
  • other maps, aerial photographs and street level imagery
  • engineers’ reports
  • local knowledge

We consider it a reasonable expectation that human life could be endangered if any of the following apply:

  • in the event of a flood caused by a failure of the reservoir, the likely loss of life is calculated to be 1.0 or more
  • the calculated likely loss of human life is between 0.8 and 1.0 and there is a significant population at risk of flooding downstream. We will normally consider a significant population to be more than 200 people, or 20 businesses. There may be circumstances when we choose to apply the precautionary principle where there is a smaller population
  • in the case of the impact on properties, the unit discharge is 3 cubic metres per second, per metre or greater. This represents the threshold at which structural damage to properties is expected to begin. You can read more about this in the Guide to Risk Assessment for Reservoir Safety Management (Environment Agency, 2013). The properties we consider are permanent or temporary residences, businesses, recreational areas, for example, houses, flats, hospitals, prisons, offices, warehouses, caravan parks, camping sites, places of work, sporting venues, places of worship and parks.
  • the consequences of flooding at infrastructure that could lead to a loss of life. For example, if there is deep or fast flowing water across road or rail infrastructure, or damage to a chemical works leading to the release of hazardous substances.

Our designation does not consider:

  • indirect loss of life which may occur because of infrastructure damage. For example, death occurring because of equipment failure if a flooded electricity sub-station loses power
  • the impacts of a flood on the wider natural or built environment

We review inspection reports relating to the reservoir. The engineer who makes a report often provides a dam category A—D, where:

Category A: a breach could endanger lives in a community

Category B: a breach could endanger lives not in a community and/ or could result in extensive damage

Category C: a breach would pose negligible risk to life and cause limited damage

Category D: special cases where no loss of life is foreseen, and very limited additional damage would be caused

When considering the dam category, we will be guided by the following principles:

We will normally designate a reservoir as a high-risk reservoir if the dam has a category of A or B and the likely loss of life is 1.0 or more.

We would not normally designate as a high-risk reservoir if the dam is category D and the following criteria apply:

  • the likely loss of life calculation is less than 1.0
  • the population at risk is not significant
  • the maximum unit discharge at any one property is less than 3 cubic metres per second per metre (3m3/s/m)
  • there are no recreational areas or infrastructure identified in the downstream flood extent

In any other case we will consider the information in more detail.

We may seek advice from a reservoir engineer or other consultant and ask their opinion as to whether the reservoir should be designated as high-risk, or not.

At the end of our review, we will form our opinion and write to you as follows:

  • where we think human life could be endangered, we will send you a notice of provisional designation as a high-risk reservoir.
  • where there is a lack of evidence or we doubt the quality of evidence, we will adopt the precautionary principle and send you a notice of provisional designation as a high-risk reservoir.
  • where we have sufficient evidence that human life could not be endangered, we will write you to confirm that reservoir is not designated as a high-risk reservoir.

When you receive our notice or letter you should read it carefully. If we send you a notice of provisional designation, it means on the evidence we have reviewed, we think the failure of your reservoir could endanger life, but it does not confirm our decision.

Our designation sets the standard of care you must give your reservoir and the level of regulation we will apply.

Our provisional designation is not a final decision, and a notice of provisional designation does not impose new rules on you.

If you disagree or think we are wrong, you can tell us by making a representation. This is your opportunity to correct any of the data we have used or to provide additional evidence that life could not be endangered. You should submit a representation to us within three months giving your reason and the evidence to support this. You are responsible for making sure the correct information about your reservoir is registered with us. If it is wrong, you must tell us about this.

If you receive a notice of provisional designation and do not submit a representation within three months, we will send you a notice of final designation after which you must carry out all the duties required to manage a high-risk reservoir.

You can appeal a notice of final designation but this may have limited effect if you did not take the opportunity to submit a representation.

Submit a representation against a provisional designation

If you think our provisional designation is wrong, you should write to us telling us your reason and providing the evidence to support your case.

The period for representation is your opportunity to engage with the designation process.

Your representation must be sent within three months of the date on the notice of provisional designation. If you don’t submit a representation at this stage, it may affect any subsequent appeal.

You can only submit a representation if you are the undertaker of the reservoir or you are authorised by the undertaker to act on their behalf.

To help you make a reasoned representation, you can request the information used by us to make our provisional designation. We will disclose this in accordance with the Freedom of Information Act, the Environmental Information Regulations and the Data Protection Act.

You should email your representation to reservoirs@naturalresourceswales.gov.uk

Your representation should be as full as possible and contain:

  • a statement identifying where we may have made an error when carrying out our assessment
  • an analysis demonstrating how the error results in a material change to the provisional designation

In general, we will consider representations on the following grounds with supporting evidence:

  • the basic data used by us in our assessment is materially incorrect
  • where a designation refers to a flood map, a representation may be made on the basis that the predicted flood path is shown to be materially incorrect or the predicted escapable volume is shown to be materially incorrect
  • the impact on persons downstream is shown to be materially incorrect.

You should provide the evidence that supports your representation. We may ask you to clarify your representation and evidence.

We will not collect further evidence ourselves in response to your representation. However, we may seek the opinion of an engineer or other consultant to help our review.

When we have reviewed the new information provided by you, we will make our final designation.

If you did not send us any written representation, we will consider this to mean you accept our provisional designation.

Final designation

After at least three months from our notice of provisional designation we will confirm the designation of your reservoir taking in account any written representation you provided.

Where we have considered a representation, we will either:

  • we will write you to confirm that your reservoir is not designated as a high-risk reservoir, or
  • send you a notice of final designation as a high-risk reservoir because we consider the evidence to be insufficient.

There is no second period for representations.

Our notice of final designation will specify our reasons for the designation. If you disagree with our final designation, you may make an appeal.

From the date we issue a notice of final designation you must comply with all duties of an undertaker for a high-risk reservoir. This requirement is suspended if you choose to appeal.

Appeal the designation of your high-risk reservoir

If you receive a notice of final designation from us and you think we are wrong, you can appeal to the Welsh Minister. Your appeal must:

  • be made in writing
  • include the grounds of the appeal
  • be received by Welsh Government within 28 days of the date on the notice of final designation

Be addressed to:

Coal Tip, Mine and Reservoir Safety Team
Welsh Government
Cathays Park
CF10 3NQ

or by email to: reservoirs@gov.wales   

The Minister will appoint a person to ensure your appeal is valid and to review your submission. The appointed person may request further information and will decide whether the appeal will be conducted by written representations or by a hearing.

The appointed person will determine whether the designation of your reservoir as a high-risk reservoir remains valid, or if our designation should be withdrawn. Both parties are bound by the decision of the appointed person.

Until the appointed person has made a determination, your responsibilities for your reservoir are unchanged but the activities imposed on you for managing a high-risk reservoir are suspended.

You are responsible for any costs you incur as part of your appeal. We will not seek to recover from you any costs we incur in supporting the appeal process.

You can only appeal a notice of final designation. If you disagree with a notice of provisional designation, you should read our guidance on how to submit a representation.

You can appeal on any grounds. If there are circumstances where an appeal may not be appropriate or successful, you may wish to request a designation review.

Designation review

We will normally review the risk designation for your reservoir if any of the following criteria apply:

  • we think it may be appropriate to designate a large, raised reservoir as a high-risk reservoir even if we didn’t think it was one previously. This is more likely if we become aware of new or changed development downstream of the reservoir which may increase the population at risk
  • we think the designation as a high-risk reservoir may no longer be appropriate. This is likely to be based on better evidence that life could not be endangered
  • the current designation is more than six years old and a review of the information on which the designation was made reveals new information

Request a review

You may request a review at any time. You should consider this if you have any information or evidence which you think we were not previously aware of.

There is no prescribed format for requesting a review, but it should contain the information and evidence which may affect our previous designation. You should email your request for a designation review to reservoirs@naturalresourceswales.gov.uk.

We propose to charge for reviewing designations after 1 April 2023. The charge will be published at that time.

We are unlikely to proceed to a review if no new information or evidence is presented to us.

If we think a review of the designation is warranted, we will follow the same three steps as if it was a first designation.

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