HUGE WATER SUPPLIES.

New Zealand Herald, Volume LXIII, Issue 19221, 9 January 1926, Page 2 (Supplement)

HUGE WATER SUPPLIES.

WORLD'S GREATEST DAMS. COLOSSAL UNDERTAKINGS. SOME ENORMOUS LAKES FORMED. The tragic bursting of a dam near Conway, in North Wales, reminds one of the tremendous importance of the engineering side of these constructions. In England the biggest dams have been constructed to supply Manchester, Lnerpool, and Birmingham with water. Manchester has already made a huge reservoir of Thirlmere, just under "the dark brow of mighty Helvellyn." There is a storage capacity, created by a huge dani at the Keswick end, of over 8,000,000,000 gallons. Lake Vyrnwy, in Montgomeryshire, had no existence until the Liverpool corporation dammed up a small tributary of the River Severn. The clam is 1172 ft. long, 161 ft. high, and 127 ft. thick at the bottom. The storage capacity is 12,000,003,000 gallons. The water leaves this artificial lake by a tunnel miles long, driven through a hill. The tunnel under the Mersey, which carries the water into Liverpool, was the first of its kind in the world. It is 900 ft. long, and took forr years to construct. Birmingham also goes to Wales, to affnents of the Wye, for its water. It

requires five dams and five reservoirs, one of which, formed by the damming of the Elan valley, is four miles long and has a capacity of 8,000,000,000 gallons. America is the land of great dams. The New Croton Dam impounds 32,000,000,000 fallons of water for the service of New "ork. Its foundation is a level platform of masonry, to lay which half a million cubic yards of rock had to be removed. The masonry dam raised upon it is 205 ft. thick at the base, 250 ft, high, and 1200 ft. long. It required a million cubic yards of masonry, and supplies New York with 250,000,000 gallons of water a day. Another vast water supply for the same city has recently been constructed in the Katskill Mountains. It is called the Ashokan Reservoir, and is 127 miles from tho city, the water taking three days in making tho journey. It supplies 500,000,000 gallons a day, and in case of necessity this can bo increased to 900,000,000.

To maka this enormous lake seven villages were razed and eleven miles of railway torn up. Its basin is 900 square miles in extent. It took 17,240 men seven years to make, and the total cost was over thirty-five million pounds. The course of the river Esopus .is blocked by an enormous masonry dam over one-third of a mile long, 200 ft. wide, and 240 ft. high. At each end of the central masonry dam is an earthern one with a masonry core. These are each 1000 ft. long and 800 ft. thick at the base. India has benefited greatlv by the erection of irrigation dams, vast areas having been rendered fertile. The Tori Reservoir, one of the largest, was formed by damming up a valley by a rampart a milo and a

quarter long and 300 ft. thick at the base, But the >.nv t'i.Mii )■ ,ok? >•

vati, in Mysore, spans a gorge 1200 ft, wide. Tt is 267 ft )v. '• .•

having a capacity of 32,548,000,000 cubic feet of water. It is for irrigation purposes.

The Assouan Dam on the Nile has added 2500 square miles to the agricultural area of Egypt. It holds back 1,000,000,000 tons of water.