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

The Department's description

Exterior description and setting

A gravity concrete dam across the headwaters of the Annalong River between Slieve Bignian and Ben Crom. Near vertical slope on wet side, and less steep slope on air side. The latter has vertical ribs at regular intervals. The mass-concrete core is faced with regularly-coursed vee-jointed concrete blocks on both sides. Dimensions are: 706ft long, 102ft basal width, 111ft high to spillway level/ 125ft high overall; impounds 1700 million gallons. In the bedrock under the dam is a 30ft deep concrete-filled water cut-off trench.

Two pairs of overflow spillways in the middle of the dam discharge into the outflow channel. At the base of the dam, between the outflows is a flat-roofed valve house, which controls the flow of water into the Silent Valley reservoir. The 27in diameter discharge pipe has a jet disperser to minimise scouring of the outflow channel; the opening through which it emerges is delineated with stepped vee-jointed concrete voussoirs. The outflow channel has vertical concrete walls faced with vee-jointed concrete blocks coped with rusticated granite blocks, and its bed is pitched with concrete.
Concrete stairs on the left bank lead up to a roadway across the top of the dam. It has parapet walls on both sides and segmental arches over the spillways.

Immediately below the dam, on the left bank, is a terrace containing a small circular fountain. This area is demarcated with vee-jointed concrete block walls in which are embedded bronze plaques commemorating (1) laying of the foundation stone, 8 Oct 1954; (2) opening of the dam, 2 Oct 1957; (3) completion of the Mourne Scheme, 27 May 1959; and (4) a diagram giving the dimensions and cross-section of dam.

A short distance further along this bank is the quarry from which stone was obtained.

Historical information

The opening of the Slieve Bignian tunnel in 1952 increased the inflow to the Silent Valley reservoir. To increase its storage capacity, the Belfast City & District Water Commissioners erected this auxiliary dam above it. Work started in 1954, the foundation stone being laid by Lord Wakehurst, Governor of N. Ireland, on 8 Oct 1954. The contractor was Charles Brand & Son (London) and the consulting engineer Messrs Binnie, Deacon and Gourley (Westminster). It was completed in 1957 and opened on 2 October of that year by Wallace Linton, Chairman of the BCDWC.

Primary Sources:
1. Bronze plaques on walls in vicinity of dam.
2. Original drawing in DOE Water Service, Westland House, Old Westland Rd, Belfast (cat. no. 2I23).

Secondary Sources:
1. Belfast City & District Water Commissioners, ‘The Mourne Scheme’ (Belfast 1959).
2. G.A. Cooper, ‘The reservoir safety programme in Northern Ireland’ - paper presented at 1987 conference of Institution of Water Engineers and Scientists.

Criteria for listing: architectural interest

A. Style
B. Proportion
C. Ornamentation
F. Structural System
J. Setting
K. Group value

Criteria for listing: historic interest

Y. Social, Cultural or Economic Importance
W. Northern Ireland/International Interest
X. Local Interest

Evaluation

Despite its utilitarian function, considerable thought has been given to the finish and overall symmetry of this dam in relation to its mountain setting. Technically, Ben Crom is one of only three wholly concrete gravity dams in the Province (the others are Altnaheglish and Spelga). Although neither the earliest nor the widest of this type of dam, it is the tallest, impounds the most water and has the most spectacular setting. It is also an integral part of the Mourne Scheme and is thus of national significance.