CPAT logo
Cymraeg / English
Elan Valley
Historic Landscape
Character area map
More photographs

Historic Landscape Characterisation

The Elan Valley: Claerwen
Llanwrthwl and Rhayader Community (Powys), Ystrad Fflur (Ceredigion) Communities
(HLCA 1133)

CPAT PHOTO 03-c-0658

Dam and reservoir constructed in the late 1940s and early 1950s to enhance Birmingham’s water supplies from the Elan valley, built in a style which harmonizes with the earlier Elan Valley reservoirs.

Historic background and key historic landscape characteristics

Little is known of the earlier archaeological history of the upper Claerwen valley most of which formed unenclosed pasture when construction began on the present reservoir in the 1940s. A somewhat smaller reservoir, provisionally named the ‘Pant-y-beddau Reservoir’, had been planned as part of the scheme designed by James Mansergh on behalf of Birmingham City Corporation in the late 19th century at the upper end of the Claerwen valley. The land was compulsorily purchased as part Birmingham Corporation Water Act 1892 but the dam was not built at that time since sufficient capacity had been achieved by the other reservoirs in the scheme.

The severe drought of 1937 provided a warning that the city would need to increase capacity, and although plans for the new reservoir, requiring a further parliamentary bill, were at an advanced stage in 1939 construction work was delayed due to the onset of the Second World War. The advances in engineering and mechanisation that has taken place during the course of the earlier 20th century permitted the construction of a broader and taller dam than had originally been envisaged, about 1.5 kilometres downstream of the dam proposed for the Pant-y-beddau reservoir. The reservoir, started in 1946 and officially opened by Queen Elizabeth in 1952 as one of her first official engagements, almost doubled the supply of water to Birmingham from the Elan valley.

About 470 men worked on the construction of the dam, 56 metres high and 355 metres in breadth, who unlike the workforce employed on the earlier reservoirs were all housed in the local community and transported to the site by road. The workforce included about 100 Italian stonemasons due to a shortage of skilled workmen because of the repairs due to war damage being undertaken in a number of British cities at the time, including the restoration work being undertaken on London’s Houses of Parliament. Building materials were mostly transported by road from the railway, 14 kilometres away at Rhayader.

The 263-hectare reservoir occupies the head of the Claerwen valley, the highest water level being about 368m above Ordnance Datum. The curving Claerwen Dam, 56 metres high and 355 metres in breadth, designed by William Halcrow & Partners, is the largest in the Elan Valley complex. It is built of concrete but at considerable extra cost in terms of both materials and labour the dam was faced in rock-faced stonework from South Wales and Derbyshire and incorporated other design features in order to harmonize with the aesthetic standards of earlier dams in the Elan Valley. Water is released from the reservoir by either of two 1.2 metre diameter pipes, each side of the dam base, which discharge into the river Claerwen. A hydroelectric turbine house incorporating a Francis 1680 kilowatt turbine has recently been built below ground level, fed by an extension to one of the outlet pipes.


Hubbard 1979; Tickell 1894; Regional Sites and Monuments Record; Listed Building lists

For further information please contact the Clwyd-Powys Archaeological Trust at this address, or link to the Countryside Council for Wales' web site at

Privacy and cookies