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Mynydd Hiraethog Historic Landscape
Character area map

Historic Landscape Characterisation

Mynydd Hiraethog: Alwen Reservoir
Nantglyn Community Denbighshire, and Cerrigydrudion, Pentrefoelas and Llansannan Communities, Conwy
(HLCA 1111)

CPAT PHOTO cs012908

Earlier 20th-century reservoir superimposed upon medieval and later enclosed landscape.

Historic background

The area falls within the 19th-century tithe parishes of Cerrigydrudion, Nantglyn, Tiryrabad-isaf (Pentrefoelas) and Henllan. The construction of the early 20th-century reservoir submerged low-lying fields belonging to Ty-isaf, Creigiau'r-bleddiau and Hafod-y-llan-uchaf farmsteads on the north and enclosed moorland on the south side of the river Alwen as well as a number of footbridges and sheepfolds.

Key historic landscape characteristics

The reservoir, built between 1911-16, covers an area of about 1.7km2 within a relatively narrow valley on the southern edge of Mynydd Hiraethog, at a height of about 360m above Ordnance Survey above the dam and 330 below the dam. The reservoir was formed by the damming of the Afon Alwen, a tributary of the Dee river system.

Early activity in the area is represented by a possible prehistoric stone circle or hut circle and a Bronze Age bronze spearhead, both discovered during the construction of the reservoir.

Curved dam of concrete blocks with Italianate valve tower was built as a water supply for Birkenhead between 1911-16 but now supplies north-east Wales. Other contemporary elements below the dam include the older, rendered brick filter house below the modern steel-framed works, the remains of barrack housing built for construction workers, a terrace of six brick workers' houses, with various other features in the landscape around the reservoir itself, including cast-iron gates and iron fencing. Like the Brenig Reservoir, it forms an important present-day resource for sporting and recreational activities including a water-ski training centre, fishing, and walks and picnic areas.


CPAT Sites and Monuments Record;
Davies 1929;
Hollett 2000;
Hubbard 1986;
Lynch 1993

For further information please contact the Clwyd-Powys Archaeological Trust at this address, or link to the Countryside Council for Wales' web site at

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