The risk of dam collapse has passed at Toddbrook
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August 7, 2019

We have all been following the news about the compromised Toddbrook reservoir dam over the past week, and happily, the risk of dam collapse has passed. Residents of Whaley Bridge will hopefully return home later.

Over the last week, measures have been taken to reduce the risk of a dangerous breach. An RAF Chinook helicopter dropped over 500 one tonne bags of aggregate onto the spillway, and the water in the reservoir was pumped out into the river Goyt.

The Toddbrook reservoir, built in 1831, feeds into the Peak Forest Canal. It is not used for drinking water. The Reservoir is maintained by Canal & River Trust and is a Site of Special Scientific Interest (SSSI). It provides habitat for herons, ducks and other animals and fish.

How we use reservoirs

Reservoirs have been used for centuries around the world to provide water storage for many reasons. They have become a key part of our strategy for managing water supply and storage. Water supply, irrigation water storage, energy production and flood control are just some of the many uses for reservoirs. There are also a wide variety of dams used to create reservoirs.

Mitigating risk

For any waterbody falling under the Reservoirs Act 1975, a dam breach assessment is required to risk assess the impact of a failure. This covers any waterbody over 10,000m3 stored above the natural ground level. A dam breach assessment identifies the risks for a dam breach. These assessments are typically made up of two stages: firstly, a risk-scoping exercise to identify the level of risk downstream of the dam. If this identifies a medium or greater risk downstream, then stage two is completed to identify where the risk is located. This is often done through hydraulic modelling to produce flood maps to help mitigate to risk.

Whilst there have been no deaths associated with dam breaches since 1925 the events at Toddbrook reservoir have shown the need for vigilance and ensuring the impact of potential dam breaches are understood. Many of the dams in the UK are over 100 years old, so monitoring and maintaining these ageing structures is vital.

We have completed many dam breach assessments on a wide range of reservoir and dam sizes across the UK. Take a look at our dam breach and flood hazard analysis case study here. If you require support conducting a dam breach assessment Envireau Water can help. Get in touch with our surface water team to find out more – contact Lee on 01332 871878 or at lee@envireauwater.co.uk.

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