Elan Valley Reservoirs - Description

Description

There are four main dams and reservoirs (constructed 1893–1904 in Elan Valley, and 1946–1952 at Claerwen) with a potential total capacity of nearly 100,000 megalitres. The dams and reservoirs are:

• Caban Coch with Garreg Ddu – 35,530 megalitre capacity
• Pen-y-garreg – 6,055 megalitre capacity
• Craig Goch – 9,222 megalitre capacity
• Claerwen – 48,300 megalitre capacity.

In addition to the four main dams, there are three other dams at the site:

• The Dol y Mynach dam – it was to be one of a series of three dams that would be built to contain the waters of Afon Claerwen. They were to be constructed in accordance with the growth of Birmingham. However the project was never completed even though the masonry foundations of the first dam were laid at the same time the Elan Valley dams were being constructed. The work had to be done in advance because the water level of the Caban Coch would have submerged the site once the reservoir was full. The three-dam project became redundant when newer materials and superior engineering allowed the construction of the single larger Claerwen dam higher up the valley in the 1940/50s.
• The Nant-y-Gro dam – this small dam was constructed in the early stages of the project to supply water to the navvies village at the site; it was used during the Second World War by Sir Barnes Wallis during trials of the explosive charges he intended to use in the bouncing bombs which later targeted the Ruhr dams.
• The Garreg Ddu dam – although looking like a viaduct, it is actually a submerged dam. Its role is to maintain a sufficient level in the Garreg Ddu reservoir so water can enter the Foel Tower and the gravity driven aqueduct to the Frankley reservoir in Birmingham. The dam is only required to operate during times of extreme drought.