Lake Vyrnwy

In 1879, George Deacon was instructed to prepare the parliamentary plans for the Vyrnwy Dam. The valley was chosen because of its size, favourable geology and its source, the River Vyrnwy, having a large water catchment area. Thomas Hawksley was appointed as engineer-in-chief and prepared the design for a stone dam. Dam construction with great blocks of Welsh slate started in 1881 and was completed in 1888. Hawksley resigned in 1885 because of a conflict with George Deacon who was appointed as joint engineer. The dam was the first large stone-built dam in the United Kingdom and cost £620,000 (equivalent to £ million in ). Earlier dams in Britain had been built using great earth embankments…

The Vyrnwy dam is 44 m high from the bottom of the valley, and 39 m thick at the base; it is 358 m long and has a road bridge running along the top. It is decorated with 31 arches each spanning 7.3 m and two small towers each with four corner turrets rising 14 ft above the road surface. The dam was the first to be constructed with drainage tunnels designed to prevent a build up of pressure beneath the base. It is listed as a Grade I historic building by Cadw. The dam was the first to carry water over its crest instead of in a channel at the side. At the bottom of the dam is a body of water known as a stilling basin necessary to absorb the energy when the water flows over the crest and into…