WATER FOR BELFAST

Hawke's Bay Tribune, Volume XIX, Issue 46, 9 February 1929, Page 7

WATER FOR BELFAST

GREAT ENGINEERING SCHEME “SILENT VALLEY” IN MOURNE MOUNTAINS. CONVERSION TO HUGE RESERVOIR. The task of transforming “The Silent Valley,” which lies in the heart of the Mourne mountains some 30 miles south of Belfast city, into a huge reservoir, has been decided upon by the Belfast Water Commissioners. ’l’he Silent Valley is a long depression, running due north and south, surrounded by very steep mountain slopes, which for 30 years and more engineers have contended is eminently suited for conversion into a reservoir. The Kinkeel River, a typical mountain burn, dashing and a|ilashing over great bowlders, pursues a winding course through the valley, and its waters already are tupped 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 bo built from the solid rock 100 feet below the surface and will reach to 90 feet above ground level. The chief difficulty lias been in penetrating to the solid rock. The engineers must penetrate in many places over 75 feet through layers of sand, gravel slurry ami bowlders, which were sutured 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, me being sunk into the solid rock. When completed they will form an absolutely watertight foundation for tho embankment. Some of the shafts will be 200 feet in depth. The use of compressed air is necessary in the sinking of the shafts and this adds to the difficulty of the work. When a shaft is sunk to a certain depth water percolates 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 u pressure sufficient to drive out the water. The excavation is then continued and additional iron segments are placed below those already in position. The pressure of air in the shafts 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 hut 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.