Beacons Reservoir Dam including draw-off tower, bridge and spillway

Dam is clay core and bunded earth construction, with pitched stonework to curved inner face of embankment, terminating in low wave-wall retaining roadway. Turfed outer face. The draw-off tower is off-set to the east of the dam, on a masonry platform projecting from its inner face. Circular tower of coursed, rock-faced masonry, with corbelled embattled parapet and battered base. Small windows in tooled stone chamfered surrounds to north-east and north-west on ground floor, and small loops to south-east and south-west on first floor. Front has machicolation under parapet, flanking stepped buttresses, and doorway with segmentally arched head dying into reveals of taller arched recess. Framed plaque above recording the opening of the reservoir in 1897. Base platform is rock-faced stonework with iron rails.

Spillway at east end of dam, comprising a long stepped cascade curving down from a stepped weir, and joined at the foot by a channel from a tunnel outlet. The weir is flanked by stone-faced circular piers, and has steps of granite. The spillway is crossed by a small stone bridge (giving access to top of dam), and has finely-worked masonry revetment walls and pitched stone channel surface. At the foot of the spillway, the western revetment wall curves around and back to a parabolic-arched tunnel entrance with masonry portal with cornice and blocking course. Revetment walls continue as far as the bridge carrying the Hirwaun Road. Masonry all high quality, rock-faced squared stone with tooled leading edges, raised plinth and big rock-faced coping stones to parapet. Bridge has shallow segmental arch with voussoirs and keystone, and the parapets terminate in square piers with massive rock-faced stone caps. Stone walls run north and south from the east end of the bridge.