Tanygrisiau Dam
| Date | 1 December 2012 | ||
| Location | Tanygrisiau, Blaenau Ffestiniog | SH 68338 44836; 52.98463°N, 3.96268°W | |
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The Afon Ystradau was dammed as part of the Ffestiniog pumped-storage hydroelectric scheme, which was completed in 1963. The resulting artificial lake, Llyn Ystradau, acts as the lower reservoir for the 360 MW power station. The gravity dam has a length of 549m, including the 79m spillway, and a maximum height of 12m.
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Stwlan Dam, looking towards Moelwyn Bach
| Date | 24 November 2012 | ||
| Location | Llyn Stwlan, Moelwynion | SH 66623 44421; 52.98047°N, 3.98803°W | |
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Stwlan Dam was built as part of the Ffestiniog pumped-storage hydroelectric scheme, which was completed in 1963. Llyn Stwlan is located in a cwm below the mountains Moelwyn Mawr and Moelwyn Bach above the village of Tanygrisiau and before construction of the dam was a very small lake. Now it has a capacity of 2 million cubic metres and supplies water at a rate of 27 cubic metres per second to drive the turbines at the power station below. The concrete buttress dam has a total length of 373m, including the spillway; a maximum width of 4m; and a maximum height of 34m.
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Ffestiniog Power Station between Llyn Ystradau and the Ffestiniog Railway. The spoil heaps of Cwmorthin Quarry can be seen in the background on the left.
| Date | 24 November 2012 | ||
| Location | Tanygrisiau, Ffestiniog | SH 67784 44307; 52.97974°N, 3.97070°W | |
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Construction for the Central Electricity Generating Board of the Ffestiniog Pumped Storage Scheme commenced in 1957 and the power station was commissioned in 1963, making it the UK’s first major pumped-storage system. Stwlan Dam was built to create the upper reservoir by enlarging the small lake, Llyn Stwlan, nestling in a cwm at an elevation of 500m in the Moelwyn mountains; while the lower reservoir, Llyn Ystradau (or Tanygrisiau Reservoir), was formed by damming the river Ystradau just to the south of Tanygrisiau village. The facility provides power to the National Grid at times of high demand and it has a combined output of 360 MW from its four generators. During periods of low demand, normally overnight, the system operates in reverse: taking electricity from the Grid, the generators are run as motors and the turbines act as pumps to drive water back up from the lower to the upper reservoir. Ffestiniog Power Station is currently owned by First Hydro, a joint venture between International Power plc and Mitsui & Co. Ltd. Having been acquired in June 2012, International Power is now a wholly owned subsidiary of French multinational electric utility company GDF Suez SA, and has been rebranded as GDF SUEZ Energy International. Mitsui & Co is one of Japan’s largest sogo shosa, or traditional general trading companies, and is itself part of the zaibatsu (corporate conglomerate) Mistui Group. Ffestiniog Power Station (First Hydro)
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Looking down the incline towards Llyn Stwlan, Ffestiniog Power Station’s upper reservoir
| Date | 24 November 2012 | ||
| Location | Llyn Stwlan, Moelwynion | SH 66089 44279; 52.97906°N, 3.99593°W | |
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Moelwyn Quarry, located on the eastern slopes of the Moelwyn mountains near Blaenau Ffestiniog, met with only limited success and closed around 1900. Exploration had started in the 1820s with a number of trial levels and the site was further developed in the 1860s when larger scale underground operations began. A slate processing mill, powered by waterwheel, was built at that time and its remains are visible below Stwlan Dam. The exit tramway descended the mountainside via a series of inclines to join the Ffestiniog Railway, the site of the actual junction now being submerged below the waters of Llyn Ystradau, Ffestiniog Power Station’s lower reservoir. Llyn Stwlan, the upper reservoir of this pumped-storage hydroelectric system built in the 1960s, now also covers part of the quarry complex. Moelwyn Slate Mine (Royal Commission on the Ancient and Historical Monuments of Wales)
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Llyn Stwlan, the upper reservoir for Ffestiniog Power Station, from Craigysgafn (B). The concrete dam and intake towers can be seen on the right, with the lower reservoir at Tanygrisiau below.
| Date | 26 June 2011 | ||
| Location | Moelwynion |
(A) SH 65821 44862; 52.98423°N, 4.00016°W (B) SH 65991 44332; 52.97951°N, 3.99740°W (C) SH 66028 43754; 52.97433°N, 3.99661°W (D) SH 63574 43762; 52.97378°N, 4.03314°W |
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The Moelwynion group of mountains in Snowdonia are to be found roughly in an area with Porthmadog and Capel Curig at its south-west and north-east ends, respectively. The highest peak in the range is Moel Siabod (872 m) and the name of the group comes from Moelwyn Mawr (Big White Hill), 770 m, and Moelwyn Bach (Little White Hill), 710 m. A rocky ridge, Craigysgafn, separates these two mountains and overlooks Llyn Stwlan, the top reservoir of Ffestiniog Power Station at Tanygrisiau below. This 360 MW pumped-storage hyroelectric power station began service in 1963 and was the first major facility of its kind in the UK. Ffestiniog Power Station (First Hydro)
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GeoTopoi 