17 Llyn Stwlan/Llyn Ystradau industrial area

Historic background

An area which was developed initially particularly in the mid-19th century for slate and later on for zinc and setts (see caption for photograph). The Ffestiniog pumped storage scheme which dominates this character area was the first such in Britain: work began in 1957 and was completed in 1963. The upper reservoir was formed by enlarging Llyn Stwlan by a concreate dam, and the lower (1033ft below) was created by damming the Afon Ystradau near the satellite village of Tan-y-Grisiau. Two vertical shaftes inside Moelwyn link the two to allow the system to work. The power station, on the west side of the reservoir, is of stell-framed construction faced with local stone, and was probably the largest stone building to be constructed in Wales since the times of Edward I. Care was taken with landscaping: the spoil from the upper dam was placed in the reservoir, and the face of the lower dam is covered by rocks from the excavation

Key historic landscape characteristics

19th- and 20th-century industrial landscape

The area has been quarried for slate (principally at Moelwyn (SH 661442), with outlying quarries at Bwlch Stwlan (SH 656442) and Chwarel Twm Ffeltiwr (SH 671446), and a quarry for setts at Brookes’ Quarry (SH681439). The sites of these quarries are evident, but none has bequeathed a significant landscape impact (again, see photograph), though the rake of inclines from the slate quarry to the Ffestiniog Railway is an impressive feature.

The pumped storage scheme, however, has had a significant landscape impact, involving a substantial dam at Llyn Ystradau and a very high dam, Llyn Stwlan (SH 6661 4440), visible from miles away (ironically, particularly from the A470 when travelling north past Trawsfynydd power station) despite everything. The power station on the lower lake has been described as 'an exercise in 1960s brutalism'. From the air, the articicial lakes are also dominant landscape features. A heavily-engineered road leads from here to the upper dam < back to the map

© Crown copyright. All rights reserved, Gwynedd Archaeological Trust, 100017916, 2005