Llyn Brianne

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Llyn Brianne
Llyn Brianne Reservoir.jpg
The Llyn Brianne rock-fill dam
LocationWales
Coordinates52°8′N 3°45′W / 52.133°N 3.750°W / 52.133; -3.750Coordinates: 52°8′N 3°45′W / 52.133°N 3.750°W / 52.133; -3.750
Typereservoir
Basin countriesUnited Kingdom

Llyn Brianne is a man-made lake or reservoir in the headwaters of the River Tywi in Wales.

Looking east over the reservoir
The Llyn Brianne spillway after its first fill at commissioning

Construction[edit]

The reservoir was constructed by Wimpey Construction in the late 1960s and early 1970s[1] in order to regulate the flow in the Tywi to support large potable water abstraction at Nantgaredig in the lower reaches of the river near Carmarthen; providing water to the Felindre water treatment works. The treated water is piped to a large area of South Wales which includes Swansea and Neath and the western periphery of Cardiff.

Structure[edit]

The dam is of crushed rock, larger rock and clay; all materials having been obtained in the area. In essence, it is a constructed mountain blocking the valley. The clay was harvested higher up the valley near Soar y mynydd chapel closer to Tregaron. Much of the rock was harvested at the site. An on-site stone-crusher was used to reduce larger rocks to the various sizes required. A round-the-clock labouring system enabled its completion almost two years ahead of schedule.

Fish conservation[edit]

Because of the importance of the River Towy salmon and trout fisheries, special protective measures were incorporated into the construction of the reservoir including a smolt trap and a restocking programme using artificially raised parr. Releases of water from the dam tend to be very cold and are also blamed by anglers for a reduction in the quality of the fishery.

Hydroelectric scheme[edit]

The spillway of the dam is a notable tourist attraction when the reservoir is spilling. The dam is the UK's tallest, standing at a height of 300 ft (91 m). In 1996 the reservoir spillway was increased by 1 metre in height and a hydro electric generating station was added at the base of the dam. When all three turbines are working, it generates 4.60 megawatts of electricity.[2]

Under the reservoir there are a couple of flooded houses. Before the water level was raised, it was possible to walk to Fannog farmhouse; a "For Sale" sign was once erected on it. It is still possible to see the roof when the water level is low.

Kayaking[edit]

The spillway has recently been used by kayakers to slide down while the water is in flood. However this specific activity is banned by Welsh Water, and they issued a statement in 2008 calling the practice "dangerous" and stating that such activities were banned at the reservoir. However, non-motorised water craft are permitted on the actual reservoir.[3]

References[edit]

  1. ^ Engineering Timelines
  2. ^ Our operations Archived 2013-10-14 at the Wayback Machine. Infinis
  3. ^ "Kayakers' 300ft dam drop attacked". BBC. 2008-11-18. Retrieved 2008-11-18.

Further reading[edit]

  • Lillicrap, R. J. The Llyn Brianne Dam and the River Towy Scheme. Llandovery: Llandovery Publications, 1998.

External links[edit]