Reservoirs – a reminder for farmers and landowners

23 August 2019

The recent problems Toddbrook Reservoir is causing the residents of Whaley Bridge provide a moment to remind farmers and landowners who have their own reservoirs of their responsibilities. CLA North Rural Surveyor Robert Frewen gives some advice...

If you have an on-farm reservoir with a capacity of greater than 25,000 cubic metres (about five million gallons or ten olympic swimming pools), it comes under the Reservoir Act 1975 and must be inspected, but even if you have one smaller than the limit, you are still likely to be liable if it fails and you unable to demonstrate that you have taken reasonable steps to maintain it.

If your reservoir is greater than 25,000 cubic metres in capacity, it must be registered with the Environment Agency (EA). The basic information required includes name, location (grid reference), your name and address, date of construction, height of dam and capacity. You must also appoint a “panel engineer” and supply their details to the EA. You need to tell the EA if your reservoir is formed by damming a flow of water (“impounding reservoir”) or has all sides built up and is filled each winter (“non impounding reservoir”).

The panel engineer is in effect a construction engineer (if the structure is high risk, you will also need a supervising engineer) who supervises and inspects the structure at least every ten years or if you spot any issues with the reservoir and are in any way unsure as to whether the structure might be at risk of failure.

The EA maintains two lists of panel engineers for landowners to choose from.

In view of the recent storms as well as the problems at Toddbrook, it would be prudent at least to carry out a detailed visual inspection as soon as possible and possibly to get a panel engineer to make an extra inspection.

Reservoirs fail for two principal reasons:

1. Overtopping. This is when either there is such heavy rain that the normal spillway is unable to cope and water flows over the top of the dam wall or when the spillway becomes blocked with the same effect. In either case, if the overtopping continues for any length of time, there is a real risk of erosion to the downstream face of the dam wall. Inspecting spillways regularly and keeping them clear is essential.

2. Internal erosion. This can be caused by a number of factors including burrowing animals such as rabbits, badgers and crayfish as well as rotting tree roots. This type of failure can quite quickly lead to total failure

Spotting the early signs of internal erosion is very important and much easier if the downstream face is both clear of vegetation and regularly mown. Rabbit and badger damage needs to be identified early: in the case of badgers, an electric fence may be needed given their protected status. Also keep an eye for wet patches appearing on the downstream face and carefully mark any that do so that you can determine if they are growing or shrinking/stable. If any water loving plants such as rushes start to grow in the downstream face or at its base, there may be water coming through

If you have a reservoir with a capacity of less than 25,000 cubic metres, it is without the legislation but in common law you still have a clear liability and in the event of a failure that causes damage or injury to third parties, it is highly likely that you will face claims. The strong advice is therefore to inspect your reservoir very carefully and if in doubt to get an engineer’s inspection too. Keep a log of inspection with photographs so that you can demonstrate careful and responsible risk management, so that if there is a failure, you can show that it was not “reasonably foreseeable” and was an “act of God”.

More advice is available here.