Ben Crom Reservoir, Silent Valley, Head Road, Ballymartin, Newry, BT34 4PU

Ben Crom Reservoir Dam

This concrete gravity dam was constructed across the headwaters of the Annalong River between Slieve Bignian and Ben Crom in the Mourne Mountains. Built between 1954 and 1957, it is one of only three wholly concrete gravity dams in Northern Ireland, alongside Altnaheglish and Spelga. Although neither the earliest nor the widest of this type, Ben Crom is the tallest, impounds the most water (1700 million gallons), and has the most spectacular mountain setting. It forms an integral part of the Mourne Scheme and is of national significance.

The dam measures 706 feet long, with a basal width of 102 feet and a height of 111 feet to spillway level, rising 125 feet overall. A near-vertical slope faces the wet side, whilst the air side slopes more gradually and is articulated with vertical ribs at regular intervals. The mass-concrete core is faced with regularly-coursed vee-jointed concrete blocks on both sides. Beneath the dam, a 30-foot-deep concrete-filled water cut-off trench runs through the bedrock. Two pairs of overflow spillways positioned in the middle of the dam discharge into the outflow channel.

At the dam's base, between the outflows, stands a flat-roofed valve house controlling the flow into the Silent Valley reservoir. A 27-inch-diameter discharge pipe fitted with a jet disperser to minimise scouring emerges through an opening delineated with stepped vee-jointed concrete voussoirs. The outflow channel features vertical concrete walls faced with vee-jointed concrete blocks, coped with rusticated granite blocks, and its bed is pitched with concrete.

A roadway crosses the top of the dam, accessed by concrete stairs on the left bank. The roadway has parapet walls on both sides and incorporates segmental arches over the spillways. Immediately below the dam on the left bank is a terrace containing a small circular fountain, demarcated with vee-jointed concrete block walls. These walls are embedded with four bronze plaques commemorating the laying of the foundation stone on 8 October 1954, the opening of the dam on 2 October 1957, the completion of the Mourne Scheme on 27 May 1959, and providing a diagram of the dam's dimensions and cross-section. A quarry from which stone was obtained lies a short distance further along this bank.

The dam was erected by the Belfast City and District Water Commissioners to increase the storage capacity of the Silent Valley reservoir, following the opening of the Slieve Bignian tunnel in 1952. The foundation stone was laid by Lord Wakehurst, Governor of Northern Ireland, on 8 October 1954, and the dam was opened on 2 October 1957 by Wallace Linton, Chairman of the Commission. The contractor was Charles Brand and Son of London, with consulting engineers Messrs Binnie, Deacon and Gourley of Westminster.

Despite its utilitarian function, considerable architectural thought has been given to the finish and overall symmetry of the dam in relation to its mountain setting, making it an important example of mid-twentieth-century industrial infrastructure of both architectural and historical significance.