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Visitors travelling around central Wales are likely to see a number of large reservoirs. Perhaps the most famous is Llyn Celyn in the Arenig mountains. This reservoir was created by flooding the Treweryn valley in 1965 to provide water for Liverpool. To do this, the village of Capel Celyn had to be flooded.
Capel Celyn was a Welsh speaking community with a school, chapel and 12 farms. The Westminster Government passed a Bill allowing the construction of the reservoir and the eviction of all the villagers. There were widespread protests at the time. Plaid Cymru leader Lord Dafydd Wigley said that the destruction of the village showed that Wales needed its own parliament, to ensure that an event like Treweryn could never happen again.
In the Elan valley above the town of Rhayader are a series of reservoirs which provide water for Birmingham. Constuction began during the 1890`s. The dams were constructed from large masonary blocks, which were transported to the construction sites on a railway built for this purpose. Demand for water increased, and the nearby Claerwen reservoir was added shortly after the Second World War.
When work began on the reservoirs, 100 residents of the Elan valley were forced to leave their homes. Buildings demolished included 18 farms, a school and church. These evictions occurred at a time when there was little protest. The many workers who came to the area to build the dams were housed in a temporary village of wooden huts, equipped with a canteen, bathhouse and hospital.
Some reservoirs have been built in Wales to generate hydro electric power. The Nant y Moch reservoir in the Plynlimon mountains supplies water through an underground tunnel to the Cwm Rheidol hydro electric power station about four miles away.
Trawsfynydd reservoir is unusual in having a double purpose. It was constructed to provide cooling water for the Trawsfynydd nuclear power station. The reservoir receives a large supply of water from the surrounding mountains, so surplus water is available to generate hydro electricity.
Water from Trawsfynydd reservoir is carried down the hillside in two huge metal pipes. The water operates the turbines in the hydro electric power station at Maentwrog in the valley below.
In the early 1900`s an aluminium factory was established at Dolgarrog in the Conwy valley in north Wales. Production of aluminium requires a large amount of electricity. Dolgarrog was chosen because the mountains above the site would provide a good supply of water for electricity generation. Several reservoirs were built to hold this water. In November 1925, a dam failed, causing a huge and powerful flood.
The failure of the upper dam caused a second lower dam to also fail. The huge volume of water rushed down the hillside, carrying boulders with it. Houses and shops in Dolgarrog village were destroyed or damaged, and 16 people were drowned. Much of the factory was damaged. The disaster made Parliament pass the Reservoirs Act in 1930, which introduced laws to ensure the safety of reservoirs.
Wales has two pumped storage hydroelectric power stations. The first of these was built at Ffestiniog. The purpose of the power station is to store surplus electricity by using it to pump water up to a high level reservoir on the mountain above. At times of greatest demand, electricity can be generated by letting the water drive turbines as it flows down again to a lower reservoir.
A larger pumped storage power station was built at Llanberis. This was constructed on the site of the Dinorwig slate quarry. The scheme again uses a lower lake in the valley and a reservoir on the mountain above. The pumps and turbines are located in a huge cavern which was constructed in the underground slate quarry.
In many parts of Wales we find what appear to be natural lakes, but are actually man-made reservoirs. These reservoirs often date back to the industrial revolution, when they were built to power water wheels for metal mines. The water wheels were used to pump water out of the deep tunnels of the mine, lift buckets of ore to the surface, and to power the surface machinery which crushed and separated the ore to extract the metals.