page_title: Elan Valley Reservoirs
section_title: Description
hierarchical_section_title: Elan Valley Reservoirs / Description
caption_attribution_description: English: Carreg ddu separating dam at Caban Coch, w:Elan Valley Reservoirs, Powys, Wales at a time of very low water. Maintains minimum level of upstream part.
context_page_description: The Elan Valley Reservoirs are a chain of man-made lakes created from damming the Elan and Claerwen rivers within the Elan Valley in Mid Wales. The reservoirs, which were built by the Birmingham Corporation Water Department, provide clean drinking water for Birmingham in the West Midlands of England. The five lakes are known as the Claerwen, Craig-goch, Pen-y-garreg, Garreg-ddu, and Caban-coch.
  Water from the reservoirs is carried by gravity to Frankley Reservoir in Birmingham via the Elan aqueduct. Pumping is not required because the network drops 52 metres along its 73 miles length from its source to Frankley. A gradient of 1:2300 maintains a flow of less than 2 miles per hour; water takes two and a half to three days to reach Birmingham. The aqueduct, which was started in 1896 and opened in 1906, crosses several valleys and features numerous brick tunnels, pipelines, and valve houses.
  Work to build the Elan Valley reservoirs was undertaken because the rapid growth of the industrial city of Birmingham in the late 19th century had led to a lack of available clean water.
context_section_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 – 9,220 megalitre capacity
  Claerwen – 48,694 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.
caption: Garreg-ddu dam seen at low water, summer 2003. Its job is to maintain a constant level in the reservoir during drought conditions so water can still enter the Elan Valley aqueduct.
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