05 Trawsfynydd power station and lake

(PRN 18271)

Historic background

The 1840 tithe map shows at least two farms (Brynhir at c. SH699351, and Llwynderw at c. SH703370) near the former course of the river which are now below the lake.  Little else is known of the early history of the area. The land on which the Maentwrog hydro-electric power station, and the lake and dam necessary to supply water to it, was purchased in the mid-1920s by the North Wales Power Company: work began in 1925 and the station was opened in October, 1928.  It originally had an 18 megawatt output from three turbines driven by generators, but a fourth was added in 1934 increasing its output to 24 megawatts.  It was refitted in 1991, and following the installation of computer software in 1996 it is now operated remotely by British Nuclear Fuels Ltd.   The lake was formed by the construction of four dams (Smith, 1971) which between them impounded the water to form Llyn Trawsfynydd. The principal dam, built cross the Afon Prysor (at the northern end of the lake), was the first large arch dam ever built in Great Britain (ibid, 232) and was96 ft high and 37 ft thick at the base.  In 1987 it was decided to replace the original dam, and this lengthened the life of the power station by 60 years.

Irish workers had been brought from County Cork to build the original dam, and some stayed on leading to an increase in the local population: the local tannery on the eastern edge of Gellilydan (on the edge of area 16) was converted to a Catholic church in the 1960s and is still a noticeable wayside shrine. Work on the construction of Atomfa Trawsfynydd (power station) begun in July, 1959, by which time Snowdonia had been designated as a National Park. Over 800 non-local workers lived in the Bronaber camp (area 20), recently vacated by the Army.  Both of the station’s reactors were in operation by March 1965 and the station was finally opened in October 1968.  Built at a  cost of £103 million, Trawsfynydd power station was the former Central Electricity Generating Board’s (CEGB) first inland power station, and the first to use a lake to obtain water for cooling the condensers of its turbo-alternators.  Although it has since been decommissioned, at its height the station discharged 70,000 gallons of effluent weekly into the lake (which usually contained c. 35million gallons of water.  The landscape immediately surrounding the station (particularly to the north) was designed by landscape consultant Sylvia Crowe and architectural consultant Sir Basil Spence (although little remains today).

Key historic landscape characteristics

lake, dam, power station Most of this character are comprises an artificial lake built in connection with two power stations in the 20th century.  There are several dams associated with the lake, and two power stations, one on the northern shore and the other outside the project area to the north on the banks of the Dwyryd.  The nuclear station has now been decommissioned, and the site is being heavily promoted as a leisure and tourist attraction, principally for fishing and boating.

© Crown copyright. All rights reserved, Gwynedd Archaeological Trust, 100017916, 2005

Back Home