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LLYN GELLI-GAIN RESERVOIR, TRAWSFYNYDD

Site Details

© Copyright and database right 2020. All rights reserved. Ordnance Survey licence number 0100022206

NPRN 424210

Map Reference SH73SW

Grid Reference SH7340532805

Unitary (Local) Authority Gwynedd

Old County Merioneth

Community Trawsfynydd

Type of Site LAKE, RESERVOIR

Broad Class WATER SUPPLY AND DRAINAGE

Period Unknown

Site Description LLyn Gelli-Gaer is located approximately two and a half miles south east of Trawsfynydd, and has a perimeter of 1.25 km. In 2018, Dŵr Cymru decided to look 'into the possible removal of the existing concrete dam (reservoir discontinuance)' in the lake. The following information was therefore supplied by Stillwater Associates Limited to Gwynedd Archaeological Trust on behalf of Dŵr Cymru, as part of a feasibility study and archaeological assessment.
'The reservoir was located within an upland area east of Trawsfynydd and Bronaber, within the Snowdonia National Park. It is a raised natural lake, impounded by a small gravity dam. The dam is a mass concrete stepped wall gravity structure 1.6m high and 27m long, with boulders placed on the downstream side. The spillway is constructed of concrete and comprises a broad-crested weir and a small downstream chute. The chute comprises wing walls and a base slab. There is also a small linear concrete structure within the reservoir some 50m upstream of the dam, the purpose of which is unknown. The removal strategy has not been confirmed, but may include removing all concrete parts above ground (possible leaving in concrete foundations/cut-off walls), with smaller infrastructure possibly also left behind, such as a small weir to control future water levels. The water body would return to a natural lake on its original footprint.'
Source: Gwynedd Archaeological Trust report entitled 'Gelli Gain Reservoir, Gwynedd: Archaeological Assessment' by Robert Evans and John Evans (report no. 1445 and project no. G2579)
M. Ryder, RCAHMW, 11th April 2019

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