page_title: Llyn Celyn
section_title: Operation of reservoir
hierarchical_section_title: Llyn Celyn / Operation of reservoir
caption_attribution_description: Memorial Chapel at Llyn Celyn for the drowned village of Tryweryn Cymraeg: Capel coffa Tryweryn ger Llyn Celyn English: Tryweryn memorial chapel at Llyn Celyn
context_page_description: Llyn Celyn is a large reservoir constructed between 1960 and 1965 in the valley of the River Tryweryn in Gwynedd, Wales. It measures roughly 2.5 miles long by 1 mile wide, and has a maximum depth of 140 ft. It has the capacity to hold 71,200,000 cubic metres of water.
  It was originally to be named Llyn Tryweryn Mawr, but in September 1964 Liverpool Corporation agreed to the name change following a letter from the Tryweryn Defence Committee.
context_section_description: The reservoir was built to help maintain the flow in the River Dee, so that drinking water could be abstracted further downstream as part of the Dee Regulation Scheme. These abstractions include one at Huntington water treatment works in Chester, operated by United Utilities, which supplies water to Liverpool and Wirral.
  The reservoir is contained behind a rock gravity dam and, at its upper end, it is bounded between Arenig Fawr and Arenig Fach, two of the mountains of south Snowdonia.
  Water is released from the reservoir into the River Tryweryn which flows into the River Dee. Most of the water passes through a small hydro-electric plant to supply green electricity to the National Grid. The released water first flows into a stilling basin and then down the narrow and rocky valley of the River Tryweryn. This section of the river provides facilities for international level white-water canoeing, and rafting at the Canolfan Tryweryn National White-water Centre. Some water in the reservoir is held in reserve to be released down the river for specific whitewater events. Because the reservoir's principal purpose is to support low river flows in the main River Dee, the best conditions for such events occur during long dry spells in summer when maximum releases are made. Usually the dam will release between 9 and 11 m³/s, although releases as low as 2 m³/s and as high as 16 m³/s have been known. During wet weather the releases are usually throttled back to a minimal maintenance flow unless a planned release for recreational activities has been agreed.
  Its four turbines are owned and run by Dŵr Cymru and generate 4.38 MW
caption: Tryweryn memorial chapel at Llyn Celyn
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