Scour valve house etc

The Department's description

Exterior description and setting

Although built as one unit, this complex actually comprises three distinct elements:

1. Valve scour house
Small one-storey rectangular building on island in middle of overflow channel. Two 36" diameter outlet pipes from dam (HB16/02/064) run into the basement of this building; their flow is controlled at valve tower (HB16/02/022). At the scour house, the pipes make a right-angle to the screening rooms. Valves at this abrupt turn can be opened to flush accumulated silt into a short length of tunnel which opens into the discharge channel. The building is of rock-faced granite blocks in irregular courses over a projecting base, and with a flat concrete roof. Embellished with stepped quoins and oversailing copings, all in ashlar granite. Two windows in north and south walls, and one at west, all 1/1 wooden-framed with plastic security sheeting. Metal roller door on east wall, with ashlar granite surround.

Accessed via footbridges from east and west sides. These are of concrete, faced with rock-faced granite. Arches have brick soffits, rusticated granite voussoirs and ashlar granite stringing over. Parapets have rusticated copings and terminal piers.

2. Outlet tunnel
When the scour valves are opened, the water discharges into a short length of horseshoe-profiled brick-lined tunnel. This emerges into the discharge channel through a pedimented arch of classical design. The arch voussoirs are of ashlar granite (with keystone), stepped into rock-faced granite spandrels in regular courses with an ashlar pilaster either side and entablature over. A stone in the pediment thereon is inscribed '1932' (the year the dam was completed). Immediately above this arch is a sloping grassed area enclosed by granite walls leading up to the scour valve house.

3. Discharge channel
The subterranean overflow tunnel from the bellmouth intake (HB16/02/023) emerge into the open discharge channel just above the scour valve house. It exits through a horseshoe shaped arch of similar design to the outlet tunnel arch. The arch spandrel continues up to a parapet embellished with rusticated copings and ashlar stringing. Just below the tunnel, the channel bifurcates around the scour valve house emplacement. The bed of each channel is pitched and stepped granite. They reunite below the scour valve outlet tunnel as a sloping channel which eventually continues as the Kilkeel River. The vertical sides of the 45ft wide channel are of concrete faced with rock-faced granite blocks in irregular courses and with rusticated copings over.

Historical information

Erected by Belfast City & District Water Commissioners as part of the Silent Valley reservoir scheme. Contractor Messrs S. Pearson & Son (London). According to McIldowie, the outlet tunnel was completed by 1926. It was only when it was decided to insert a bellmouth overflow instead of a weir that the overflow tunnel, arch and channels either side of the scour valve house were built. These were completed, along with the dam, in 1932, and opened in 1933. The parapet at the head of the discharge channel dates from 1954.

Primary Sources:
1. Bronze plaques on valve tower wall.
2. Original drawing of the tunnel and weir in DOE Water Service, Westland House, Old Westland Rd, Belfast (cat. no. 1C1, 2D83 and 3A76).

Secondary Sources:
1. G. McIldowie, ‘The construction of the Silent Valley reservoir, Belfast water supply’ in Proc. Institution Civil Engineers, N. Ireland Branch (Belfast 1934).
2. Belfast City & District Water Commissioners ‘The Mourne Scheme’ (Belfast 1959).

Criteria for listing: architectural interest

A. Style
B. Proportion
C. Ornamentation
D. Plan Form
E. Spatial Organisation
J. Setting
K. Group value

Criteria for listing: historic interest

Y. Social, Cultural or Economic Importance
V. Authorship
X. Local Interest

Evaluation

An integral part of the reservoir, this complex is possibly the most architecturally interesting of all the structures in the Silent Valley - the overflow and outlet tunnel arches are particularly impressive and have been executed to the highest of standards. Their appearance is enhanced by the landscaped grounds below the dam. Historically these structures are also of interest in their association with the second phase of the Mourne Scheme (the first being the impounding and diversion of the Kilkeel River to Belfast in 1901). They also form part of a larger grouping of contemporary water-related buildings.