Elan Valley Reservoirs

Beez Neez now Chy Whella
Big Bear and Pepe Millard
Wed 26 May 2010 22:18

Elan Valley Reservoirs



The beautiful Elan Valley Reservoirs are a chain of man-made lakes and reservoirs in the Elan Valley, Powys, Mid Wales, - "The Welsh Lake District", using the rivers Elan and Claerwen. The reservoirs are Claerwen, Craig Goch, Pen-y-Garreg, Garreg Ddu and Caban Coch, the one we visited a couple of miles from our hotel and the red kite feeding station.



Our little hire car which kept us safe for the 1721 miles we did in the UK and a friend sheltering from the hill winds

The work carried out over a hundred years ago to build the Elan Valley dams and reservoirs was only part of the huge undertaking. Almost as impressive was the challenge of delivering the enormous quantities of water by gravity alone, across very hilly country and over many river valleys, to the new Frankley Reservoir on the outskirts of Birmingham. This involved building the seventy three mile long Elan Aqueduct, down which the water travels at less than two miles per hour, taking one and a half days to get to Birmingham. It runs from the Elan Valley to Frankley in Birmingham. There are several signs of the aqueduct between these points, in the form of brick aqueducts, exposed pipelines and red brick valve houses on hillsides. Birmingham's tap water is noted for being exceptionally soft, with a low percentage of dissolved minerals.

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 – the masonry foundations and the base of this dam were laid in the Claerwen Valley at the time that the Elan Valley dams were being constructed. It was to be one of a series of three dams which were to hold back the waters of the Afon Claerwen making even more water available to the city of Birmingham in future times. The project was never completed but the base was laid in advance because the water level of the Caban Coch would have submerged the site once the reservoir was full. The project became completely redundant when newer materials and superior engineering led to the construction of the Claerwen dam higher up the valley.
  • The Nant-y-Gro dam – this small dam was constructed in the early stages of the project to supply water to the dam workers village at the site; it was most famously used during WWII by Sir Barnes Wallis.
  • The Garreg Ddu dam – although often referred to as a viaduct, the archways of this structure are built on a submerged dam; this hidden dam maintains the level of the reservoir behind it in times of extreme drought, and guarantees water can be extracted at the Foel Tower at sufficient height to enter the gravity driven aqueduct to the Frankley reservoir in Birmingham.
The wind that came down the valley over the water was breathtaking
The hills behind the dam showing Bear limping along, were incredibly steep

The reservoirs were constructed between 1893 and 1904 by the City of Birmingham's Water Department to supply clean water to the Birmingham area, by gravity feed along the Elan Aqueduct with a gradient of 1 in 2,300, that is a drop of only fifty two metres over the length of seventy three miles. Before the construction of the dams, the standard gauge Elan Valley Railway was built to all dam sites from a junction of the Mid Wales Railway, at Rhayader. The railway was also built along the dams themselves at varying heights, on wooden scaffolding supported by concrete parapets. The railway itself went as far as the never-completed Dolymynach dam (lower down the valley from the later Claerwen dam), which had to be built concurrently with the Elan dams as the Caban Coch reservoir would otherwise have flooded this construction site. However, this railway was never subsequently needed, and road transport only was used for construction of the Claerwen dam over forty years later.

The construction workers lived in a village of wooden huts, which had a guard to prevent the illegal importing of liquor. This later became the permanent Elan Village. When construction of the dams was complete, most of the workers moved on to the Derwent Valley in Derbyshire. The scheme was opened by King Edward VII and Queen Alexandra on the 21st of July 1904.



World War II

They played an important role in World War II when the 35 foot high Nant-y-Gro dam was used by Barnes Wallis to test his idea of detonating explosives against a dam wall in order to breach it. These experiments culminated in the Dambusters - great movie - breaching of the dams in the Ruhr Valley. The remains of the breached Nant-y-Gro dam can still be seen today in the same state as it was left in 1942. The dam is now partially obscured by trees, but its location is marked by an interpretative plaque. The Derwent Dam was also used by the Dambusters for practice, though it was not breached. After the Dambuster Raid steel cables were placed across Caban Coch reservoir to prevent enemy seaplanes landing on the lake.




Aborted expansion scheme

In the early 1970's it was proposed that the Craig Goch reservoir should be substantially increased in size with a new and higher downstream dam together with another dam to the North-West, impounding water that would otherwise have flowed down the Ystwyth valley. This scheme would have created a huge reservoir dwarfing all others in Mid Wales, and flooding miles of wild upland valleys. The proposals were eventually abandoned in the face of reducing projections for industrial water demand and an increasing awareness of the environmental issues that such an expansion might create.







The Shelley statue by the Visitor's Centre at Caban Coch Dam


The reservoirs today

The reservoirs are now owned by Dwr Cymru Welsh Water. Although the filtration works further down the valley is run by Severn Trent Water. A scale model of the reservoir network, in the form of ornamental ponds, is in Cannon Hill Park in Birmingham.




In popular culture

  • Elizabeth Clarke wrote The Valley (published by Faber & Faber, 1969) an account of Welsh hill farming life in the valley between the two main periods of construction. Many references are made to the dams, as well as an account of the later enquiry from the hill farmers' point of view.
  • Francis Brett Young researched the Elan Valley as the basis for his novel The House under the Water [Heinemann, 1932] imagining how the scene may have appeared in 1887.
Caban Coch seen in all its glory