Decommission a large raised reservoir
Discontinuance and abandonment
When your reservoir has reached the end of its useful life and has no particular use, or the cost of maintenance outweighs the value of its benefits, you need to consider its decommissioning. There are three main ways of doing this.
You can retain the reservoir but prevent it from filling, known as abandonment, or
you can retain a small reservoir or leave an empty basin, known as discontinuance.
Your decommissioning should aim to restore the ecosystem that was present prior to the construction of the reservoir. Merely removing a dam is insufficient to restore the impacts caused by the prolonged impoundment of water which is often measured in centuries.
Decommissioning includes proper restoration of the natural environment including the aquatic habitats that would have been present along the downstream watercourse and within the reservoir basin prior to its construction.
Your decommissioning plans should restore and / or improve:
- a natural, ecologically sustainable flow regime - in terms of the absolute quantity of water (baseline flow) and flow variability
- river continuity and biodiversity by helping migration of aquatic species, fish spawning and re-establishment of natural processes such as sediment distribution
- control or eradication of invasive non-native species – plant and animal
- natural nutrient distribution
Your reservoir may originally have been a wetland, natural lake or pond, later raised behind a dam. You may see evidence of this using old maps or local records. These are important habitats which will benefit from restoration.
Your decision should consider the reservoir’s original purpose and how that has changed over time. The reservoir may provide new benefits and value for which it was never designed, or its continued presence may hinder a more sustainable and natural environment within the reservoir footprint and the downstream watercourse.
Discontinuance
Discontinuance is the alteration of a reservoir so that it can no longer hold 10,000 cubic metres of water above the natural level of the surrounding land. The alteration may prevent the reservoir from holding any water at all or it can allow a small reservoir to be kept as long as the capacity is less than 10,000 cubic metres. Water below natural ground level, e.g., a natural lake, is not included.
When discontinuance is certified as complete by an engineer, we remove the reservoir from the register of large raised reservoirs and it is no longer regulated by us under the Reservoirs Act 1975.
If you need to retain a small reservoir, you should review your management of it to ensure the impacts are minimised. You will need to manage:
- sediment retained within the reservoir and sediments in the downstream watercourse to reflect river continuity and seasonal variation as described above
- environmental flow releases – to compensate for loss of natural flow in terms of absolute quantity (a baseline flow regime) and flow variability (including seasonally high and low flows)
- fish and eel passage
Abandonment
Abandonment is the alteration of a reservoir, so that it remains in place but is incapable of filling with water or it cannot fill to a level which may pose a risk, as judged by a qualified civil engineer. The alteration does not remove the dam and an abandoned reservoir can be brought back into use in the future if needed.
An abandoned large raised reservoir remains regulated under the Reservoirs Act 1975, and you may still need to arrange for inspection and supervision by qualified reservoir engineers. The opportunity for abandonment is often limited by the design of the reservoir. In the first instance, you should seek the opinion of a qualified civil engineer as to whether abandonment is possible.
Further guidance
More detailed guidance on removing and repurposing of reservoirs is available from Gov.uk
Appoint a Qualified Civil Engineer
For both discontinuance and abandonment, you must appoint a qualified civil engineer (known as a QCE) to design, supervise and certify the work.
You should appoint the QCE at an early stage so they can advise you properly and provide technical advice on the different options. They must approve and certify the works.
Notify us
You must notify us about the appointment of the QCE and provide the following information:
- The name and location of the reservoir, including its national grid reference
- The name and address of the reservoir undertaker
- The name and business address of the QCE appointed for the work
- The date the QCE was appointed
You must do this within 28 days of appointing the QCE.
Your notification must be accompanied by the appropriate fee. The fee includes our administration costs for the receipt, validation and acknowledgement of the notification and of the engineer’s certificates.
Planning and permissions you may need
Altering or removing a reservoir dam is an activity which requires various permissions before works at the reservoir can start. We recommend you take advice from the relevant regulators mentioned below.
You will need to support your applications for permissions with evidence of the design, the method and the impact. Each consenting authority can advise on what you will need to provide.
Permissions you may need from us
Impoundment licence
Under the Water Resources Act 1991, you may need permission to remove or alter an impounding structure.
Read our guidance on impoundment licences.
You can also use our pre-application advice service:
Water discharge permit
This water is considered a “trade effluent”.
We advise you take pre-application advice from us.
Flood Risk Activity Permit (FRAP)
You can see the limit of main rivers using our online map viewer.
Fish movement
Read our guidance on how to apply for permission for the safe removal of fish
Waste Management
Your decommissioning project may generate a range of waste materials, or you may need to store or treat waste on site. These activities are likely to require additional authorisations and/ or permissions.
You may need to register the activity as exempt from the need for a permit.
Read our guidance on waste permits.
Similar rules apply if you intend to import waste as part of the work, for example using construction rubble waste for an access track or waste soil for landscaping.
As a waste producer you will be required to comply with your Duty of Care for Waste.
Read our guidance on the Duty of Care.
Discontinuance may include the full removal of the dam materials, especially if they contain hazardous or non-local wastes which prevent full environmental restoration, or if that is not practicable then their treatment and redistribution on site.
Invasive Non-Native Species (INNS)
INNS can be plants or animals and can cause damage and destruction. There are controls on how they must be treated, moved or eradicated.
Assent for work in a Site of Special Scientific Interest
Use our online map to find if your reservoir is in or near a protected area.
If the planned works affect a SSSI or other protected feature, you must notify us and ask for assent under the Wildlife and Countryside Act 1981.
Read our guidance on how to obtain SSSI assent.
Internal Drainage District Land Drainage Consent
If you are planning to work on an ordinary watercourse within an Internal Drainage District (IDD) you should read our guidance on how to apply for Land Drainage Consent.
Permissions you may need from others
Legal advice
Other people may have rights at your reservoir or for the water it contains. You should contact your solicitor to check this and take advice.
Planning consent or permitted development rights
Your local planning authority can advise you on whether you need planning consent or if the work can be done under permitted development rights.
Listed building consent
Your local authority is normally the regulatory body to issue listed building consent although it can also be Cadw.
Scheduled ancient monument consent
If any of the structures at your reservoir are scheduled or if the works may have an impact on a scheduled ancient monument, you should discuss the work with Cadw to establish if consent is needed.
Ordinary watercourse consent
Works on an ordinary watercourse may require consent from your local authority. An ordinary watercourse is one which is not classed as a main river.
You can see the limit of main rivers using our online map viewer.
Health and safety
If your reservoir is a place of work, you will also need to comply with health and safety requirements.
The Health and Safety Executive can provide guidance.
Discontinuing a large raised reservoir
Discontinuance is the legal term under the Reservoirs Act 1975 for the works which may result in the reservoir being
- unable to hold water above natural ground level
- altered to retain a small reservoir with a capacity is less than 10,000 cubic metres.
Reduce the water level
The QCE may determine that the lowering of the water level should be controlled and issue an interim certificate given under section 13(1A). This certificate will specify:
- the level to which water must be reduced
- the date by which it must be reduced
- any conditions which must be applied
The QCE may issue further interim certificates for different water levels. A copy of each new certificate must be sent to us. The QCE will normally send the copy to us directly, but you should check this happens.
You must not allow the reservoir to fill above the level given in the most recent interim certificate.
Releasing water must be done in accordance with a water discharge permit. A slower, more gradual removal of water allows a more natural response. A geomorphologist experienced in river morphology may be able to provide advice on how to achieve a more natural finish.
Old maps often show the land before the reservoir was built; these can help you understand how the land may revert.
Complete the alteration works
Under the supervision of the QCE, you should complete the recommended works, taking care not to cause pollution, damage or nuisance. You should use contractors that are experienced in working on dams or other water retaining structures and who are aware of the risk of working in a water environment.
Obtain a certificate of discontinuance
When the QCE is satisfied that the works have been completed, you will be given a “section 13(2) certificate of discontinuance”. It is good practice if the engineer also provides an annexe to the certificate summarising the works and to confirm whether a small reservoir has been retained and what, if any, its remaining capacity is. You should ask for this annexe if one is not provided.
On receipt of the certificate, we will check the facts and remove the reservoir from the register. You should keep all records of the work.
Unless and until the discontinuance certificate has been issued, the reservoir remains a large raised reservoir subject to the level of regulation imposed by its risk designation.
Abandoning a large raised reservoir
Obtain an engineer’s report
Before you abandon a reservoir, you must appoint a QCE to inspect the reservoir and obtain a report of the inspection. The inspection report will contain the actions you need to take to safely abandon the reservoir.
Complete the recommended measures
You must complete any matters to be taken in the interests of safety within the time limit recommended by the QCE and obtain a certificate to show the measures are completed satisfactorily.
When the measures are complete and certified, we will amend the register to show that your reservoir has been abandoned and we will continue to monitor any remaining statutory requirements.
The report will also contain recommendations for maintenance, monitoring, surveillance and record keeping. You should ensure these are all completed.
Read our guidance on how to understand an inspection report.
Continue to manage the reservoir safely
You must not refill an abandoned reservoir. If you wish to bring the abandoned reservoir back into use, this is a controlled activity for which you must appoint a construction engineer and tell us.
You must report any incidents at your reservoir which could affect its safety.
If your reservoir is designated as a high-risk reservoir, you must:
- continue to appoint a supervising engineer
- continue to monitor, maintain and keep records
- continue to arrange for periodic inspections
The QCE may reduce the frequency of monitoring, maintenance and record keeping.
Review your flood plan
While your reservoir is being discontinued or abandoned you should revise your flood plan to account for any new risks which may appear while works are underway.
Read our guidance on how to review your flood plan
Legal consequences
It is an offence to:
- discontinue or abandon any large raised reservoir, regardless of its risk designation, without appointing a QCE
- fail to notify us of the appointment of a QCE at least 28 days before discontinuance or abandonment begins
- fail to maintain the reservoir water level below the level given by the QCE in an interim certificate
- provide current correct information to be held on the public register
- fail to obtain any permit or consent or to register an exemption, as may be required, and to fail to comply with the conditions of the permit or exemption as the case may be
If we become aware that a reservoir is being altered, but that no QCE has been appointed to design, approve and supervise the work we may serve notice on you requiring a QCE to be appointed within 28 days.
If you fail to carry into effect any measures to be taken in the interests of safety, we may serve notice on you requiring the works to be completed within a fixed time limit.
We seek to recover our costs for any enforcement action we take.