Tag Archives: Stwlan Dam

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Stwlan Dam

Stwlan Dam, looking towards Moelwyn Bach

Date

 24 November 2012
Location

 Llyn Stwlan, Moelwynion

 SH 66623 44421; 52.98047°N, 3.98803°W

Information

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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Moelwyn Quarry

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

Information

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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