Engineering Wonders of the World
Volume III

GREAT BRITISH DAMS AND AQUEDUCTS. 181 Water enters the aqueduct at an ornamental tower, 170 feet high, which rises 100 feet above high-water level at a point in the lake about three-quar- ters of a mile from the The Water Tower. dam. Outside the tower are two sets of six vertical tubes, and inside two sets of four similar vertical tubes, each 9 feet long, placed end to end and moving in guides. At the bot- tom the sets are connected by a pipe. Water can be admitted at any joint by raising the pipes above, a system which enables the supply to be drawn from near the surface, where the water is purest, whatever be the level of the lake. Within the tower the water is strained through wire gauze having 10,000 meshes to the square inch, and then passes through valves into a concrete culvert leading to the Hirnant tunnel, with which begins the aqueduct proper. The aqueduct is made up entirely of tunnel and syphon sections. The tunnels, which have an aggregate length of only about * 3i miles, are designed Aqueduct. ° to carry at least 40,000,000 gallons a day. Two lines of 42-inch pipes have been laid, and a third will be added when required. On the hydraulic gradient are five balancing reservoirs—at Parc Uchaf (9| miles from the lake), Oswestry (18 miles), Malpas (36| miles), Cotebrook (48 miles), and Norton (59 miles). The Oswestry reservoir is formed by an earthen embankment, able to impound 46,000,000 odd gallons. Beyond the reservoir are filter beds and a clean water reservoir, through which the water passes on its way to the next syphon. Between the Cotebrook and the Prescot reservoirs, a dis- tance of 20 miles, the ground nowhere reaches the hydraulic gradient. At Norton Hill, THE WATER TOWER AT LAKE VYRNWY. {Photo, J. Maclardy.) It rises 60 feet above high-water level, and has a total height of 170 feet. about midway, it was decided to construct a reservoir. As the surface lay 110 feet below the gradient, a handsome tower of red sand- stone was built to the required level. It supports an enormous circular tank, 80 feet in diameter and 31 feet deep at the centre. The basin-shaped steel bottom has a depth of 21J feet, the upper cast-iron portion a height of 10J feet. The weight of the tank and its contents (650,000 gallons) is borne by rollers resting on a cast-iron bed-plate sup- ported by the coping of the tower. This arrangement allows for the expansive and contractive movements of the metal.