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The Silent Valley Reservoir is a reservoir located in the Mourne Mountains near Kilkeel, County Down in Northern Ireland. It supplies most of the water for County Down, surrounding counties and most of Belfast. It is owned and maintained by Northern Ireland Water Limited (formerly DRD Water Service). The reservoir was built between 1923 and 1933 by a workforce of over one thousand men, nine of whom died.

Silent Valley Reservoir
LocationCounty Down, Northern Ireland
Coordinates54°08′N 6°00′W / 54.133°N 6.000°W / 54.133; -6.000Coordinates: 54°08′N 6°00′W / 54.133°N 6.000°W / 54.133; -6.000
Lake typereservoir
Basin countriesUnited Kingdom, Ireland


With Belfast's rapid growth, there was a fast-growing demand for more and more water. The two existing upload water catchments were becoming increasingly insufficient. Local civil engineer, Luke Livingston Macassey was appointed the task of finding a source of water large enough to sustain Belfast. Five potential sites were surveyed in County Down, and County Antrim. Macassey ultimately decided on the Mournes in Down. The reason the Mournes proved so popular with Macassey was the cleanliness of the water and the high amount of rainfall – both paramount factors in water sources. Upon deciding on the site, water commissioners agreed on securing a 9,000-acre (3,600 ha) catchment area. This area is surrounded by the Mourne Wall, built entirely by hand, taking eighteen years to complete. At the time the catchment was capable of providing some 30 million imperial gallons (140,000 m3) of water per day, but this was too much. A scheme was developed and divided into 3 stages:

  1. The first stage was to divert water from the Kilkeel and Annalong river through pipes to a reservoir near Carryduff. These water pipes were capable of supplying 10 million imperial gallons (45,000 m3) of water per day.
  2. The second stage was to build a storage reservoir across the Kilkeel River, after new pipes laid there were able to supply another 10 million imperial gallons (45,000 m3) of water per day.
  3. The third stage was planned to be another storage reservoir in Annalong to impound the Annalong River. However, after the difficulties encountered in building the Silent Valley dam the second dam was not built. Instead, in the 1950s, a second dam was built at Ben Crom, further up the Kilkeel river valley. Also a tunnel was driven under Slieve Binnian to bring water to the Silent Valley reservoir from the Annalong river.
Panorama of the Silent Valley Reservoir

The Binnian TunnelEdit

Between 1947 and 1951 over 150 men drove a tunnel almost two and a half miles long underneath Slieve Binnian. The tunnel was built to carry water from the Annalong valley to the Silent Valley Dam, which had been completed in 1933, 14 years earlier. This was to further supply the growing demands of Belfast's water supply. Two work squads began at each end of the tunnel, and met half way almost 800 metres under the mountain. The technology in the day was lacking in every standard, and was led by candlelight. When the two squads met, they were mere inches off. The tunnel measures 8 feet (2.4 m) square – and 2.25 miles (3.62 km) long. Its entry is at Dunnywater and its exit is on the roadside, a short distance from the visitor's centre. The Binnian Tunnel was officially opened on Thursday, 28 August 1952.

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