Information from an Archaeological Assessment of Brithdir Mawr Reservoir Discontinuance, Flintshire, conducted by Gwynedd Archaeological Trust, 2019:

'As specified in data supplied by Stillwater Associates Limited, Brithdir Mawr reservoir was constructed in 1897 and consists of a 94m long, 9m high earthfill embankment with a puddle clay core. The inlet for this reservoir is described as uncontrolled from the surrounding 200 hectares. It has a 7.6m long primary, a 9.75m secondary spillway and two low level outlets with inline sluice valves. The reservoir measures c. 150m long East to West and 100m wide North to South.'

RCAHMW, 15th Janaury 2020