Engineering Wonders of the World
Volume III

GREAT BRITISH DAMS AND AQUEDUCTS. 189 plate to move and release a trigger. The weights rotate the pulley at a speed governed by a hydraulic cataract, and bring the disc valve slowly into a vertical position, checking the flow of water. The third class of automatic valves to be noticed are those in the southern legs of the syphons. These valves have doors which open only in the direction of normal flow, and close against their seatings if a rupture causes the water to flow backwards toward the lowest part of the syphon. The scheme, originated and carried out by the late Mr. James Mansergh, Past President Inst.C.E., for which Parliamentary powers were obtained in 1892—with supplements at later dates—included the construction of a dam on the Elan below the confluence of the two streams, of two more higher up the Elan Valley, and three in the Claerwen Valley, to impound six reservoirs forming two flights of gigantic water stairs up the valleys in question. The watershed acquired has an area of over 70 square miles, and an average annual At the present time two pipe lines, convey- ing 20,000,000 gallons a day from Thirlmere to Manchester, have been completed, and ar- rangements are in progress for laying a third line. The scheme was prepared by the late Mr. J. F. Latrobe Bateman, F.R.S. (the engineer of the Longdendale works), in con- nection with Mr. G. H. Hill, who carried it out on behalf of the Corporation. The cost of the watershed and lake, of all necessary way-leaves, of the construction of tunnel and cut-and-cover sections, and of two pipe lines, amounted to about £3,500,000. It is esti- mated that the total cost of the completed scheme will be £5,000,000. The next great British aqueduct to be noticed is that commenced in 1893 and opened in 1904, which brings water 73 miles from the Elan and Claerwen valleys, in Wales, to Birmingham. The two rivers named are tributaries of the Wye. The Birmingham Aqueduct. rainfall of 611 inches. At 36 inches per annum the fall would yield about 100,000,000 gallons a day—more than ample to meet all requirements. At the time of writing, all the dams in the Elan Valley have been completed, and the foundations laid for one in the Claerwen. The lowest of the dams, the Caban Coch, is 566 feet long at the top, 122 feet above the river bed, and 122J feet thick at the base. It impounds 8,000,000,000 gallons of water, and forms a lake which extends some dis- tance up both valleys. Below power - station, wherein the water let out into the river is utilized to generate electricity for use on the filter beds and for lighting purposes, and to operate a hydraulic accumulator for working the valves at the dam and at the inlet to the aqueduct. One and a half miles farther up the valley is a submerged dam—not referred to previ- * ously—which rises to an elevation 40 feet The Caban Coch Dam. the dam is a