MOUNTAIN OF MOURNE

Waipa Post, Volume 38, Issue 2269, 16 February 1929, Page 2

MOUNTAIN OF MOURNE

BELFAST’S WATER SUPPLY The task of transforming “The Silent Valley,” which lies in the heart of the Mourne mountains some 30 miles south of Belfast, into a large reservoii*, has been decided upon by the Belfast Water Commissioners. The Silent Valley is a long depression, running due north and south, surrounded by very steep mountains slopes, which for 30 years and more engineers have contended is eminently suited for conversion into a reservoir. The Kilkeel River, a typical mountain burn, dashing and splashing over great boulders, pursues a winding course through the valley, and its waters are already tapped by the city. An essential part of the scheme is the construction of an embankment across the southern end of the valley, and this has presented exceptional difficulties. BORING DOWN TO SOLID ROCK The embankment which will be 1100 feet in length, will be built from the solid rock 100 feet below the surface and will reach 90 feet above ground level. The chief difficulty has been in penetrating the solid rock. The engineers must penetrate in places over 75 feet through layers of sand, gravel slurry and boulders, which are saturated with water. Novel methods are being used in this section. A series of circular shafts which, as they are excavated, are fitted with cast iron segments, are being sunk into the solid rock. When completed they will form an absolutely watertight foundation for the embankment. Some of the shafts are 200 feet in depth. The use of compressed air is necessary in the sinking of the shafts and this adds to the dffieulty of the work. When a shaft is sunk to a certain depth water precolates into the bottom. COMPRESSED AIR STOPS WATER It is necessary then to seal the shaft so that compressed air can be admitted to it at a pressure sufficient to drive the water out. The excavation is then continued and additional iron segments are placed below those already in position. The pressure of the air in the shaft varies from a few pounds per square inch to a maximum of 35 lbs. When the latter pressure is used workmen cannot remain in a shaft for more than two hours. The exact cost of completing the reservoir cannot be determined but the engineers place it at about £l,365,000. The valley will provide storage for 3,000,000,000 gallons of water and this, it is believed, will be sufficient to safeguard the city from a shortage in the dryest season.