Overflow pipe, Silent Valley Reservoir, Head Road, Kilkeel, Newry, Co Down, BT34 4PU

This is an overflow pipe, an integral part of the Silent Valley Reservoir, constructed between 1926 and 1932 as part of the second phase of the Mourne Scheme – a project initially focused on diverting the Kilkeel River to Belfast in 1901. It is also functionally related to a nearby discharge channel. As far as can be determined, it is the only reservoir overflow device of its type in Northern Ireland.

The structure consists of an inverted, circular bellmouth opening set into the pitched side of the reservoir near its south-east corner. The external face is built with regularly coursed, rock-dressed granite blocks, finished with darker coloured ashlar granite blocks forming a coped edge with a rounded outer rim. The interior of the bellmouth features four concrete baffle ribs and is lined with blue brick over pre-cast concrete blocks. The intake diameter at the base is approximately 80 feet. The orifice narrows into a 16-foot diameter brick-lined concrete pipe, which turns at a right angle at the bottom before entering a rock-cut tunnel under the dam. Beyond the dam, the pipe adopts a horseshoe profile and discharges into an open channel above the scour valve house.

The overflow pipe was built by Messrs S. Pearson & Son (London) for the Belfast City & District Water Commissioners, and designed to discharge excess water when the reservoir level rises within 8 feet of the top of the dam. Original plans had included an overspill weir on the west face of the dam, but this overflow pipe proved to be a more economical alternative. It was opened in 1933 alongside the dam. The structure is of industrial archaeological interest, and exemplifies innovative engineering, demonstrating careful thought in its form and execution. Historical plaques are affixed to the valve tower wall, and original drawings of the tunnel and weir are held by the Department of the Environment Water Service in Belfast.