An Act of Parliament was passed in 1892 for The Birmingham Corporation to compulsory purchase the water catchment area of the Elan and Claerwen Valleys.
In 1893 the building work began, 100 occupants of the Elan Valley had to move, only the landowners received compensation payments. Many buildings were demolished, 3 manor houses, 18 farms, a school and a church. Six reservoirs were to be built with Caban-Coch, Penygarreg and Craig Goch in the Elan Valley and Dol-y-mynach, Ciloerwynt and Pant-y-beddau in the Claerwen Valley.
The first phase of building, Caban Coch, Garreg Ddu, Pen y Garreg, Craig Goch dams were completed with the foundations of Dol y Mynach dam along with Dol y Mynach Tunnel which supplies water from the Clearwen Valley to Garreg Ddu reservoir and the 73-mile aqueduct to the Frankley reservoir, near Birmingham were all built by 1904. On 21st July 1904 King Edward VII and Queen Alexandra opened the Elan dams and water started flowing along 73 miles of pipeline to Birmingham.
The building of the second phase dams was delayed due to the 1st and 2nd World Wars and work didn't start again till 1946. With advancements in engineering only one large dam (Claerwen Dam) was needed rather than 3 smaller ones in the Claerwen Valley. Claerwen Dam was opened by Queen Elizabeth on 23rd October 1952.
Garreg Ddu Dam also known as the submerged dam is the second of the Elan Valley Dams.
The completely submerged dam which plays a vital role in maintaining a constant supply of water to Birmingham. Garreg Ddu holds water back on the upstream side so that water can always be extracted at the Foel Tower.
Height of weir - 82 ft above river bed
Total capacity - 4,585 million gallons
Pen y Garreg Dam third of the Elan Valley Dams, also known as the middle dam. This dam houses an access tunnel to the central tower which is lit by apertures in the downstream side of the dam.
Height - 123 ft above river bed
Length - 417 ft 6 in.
Total capacity - 1,320,000,000 gallons
Craig Goch Dam fourth of the Elan Valley Dams, also known as the top dam. Craig Goch is seen as the most attractive of the dams, with an elegantly curved retaining wall and a series of arches carrying a roadway across the top of the dam.
Height - 120 ft above river bed
Length - 417 ft 6in
Total capacity - 2,000,000,000 gallons
Dol-y-Mynach Dam the first of the Claerwen Valley Dams.
Also known as the unfinshed dam. Dol-y-Mynach, which was to be 101 ft (31 metres) high and 938 ft (286 metres) long was never finished. This was to be the first of three dams (Dol-y-mynach, Ciloerwynt and Pant-y-beddau) to be built in the Claerwen Valley but due to both world wars the three dams were never built. Claerwen dam was built instead. There is a small tower just upstream of Dol-y-Mynach dam which marks the entrance of the Dol-y-Mynach Tunnel. This feeds water from the Claerwen directly into the Garreg Ddu reservoir during droughts. The Tunnel is just over 1 mile long.
Height - 10.7 meters
Total capacity - 150 million gallons
Claerwen Dam the second of the Claerwen Valley Dams.
Claerwen dam holds almost as much water as the combined total of the Elan Valley dams. Claerwen Dam took six years to build, using a workforce of 470. Claerwen Dam was opened by the newly crowned Queen Elizabeth on 23rd October 1952.
Height - 56 metres above river bed
Length - 355 Metres
Total capacity - 48,300,300,000 Litres