Engineering Wonders of the World
Volume III

THE GREAT IRRIGATION WORKS OF INDIA. 235 HYDRAULIC WEIR SHUTTERS. In the foreground is a self-acting shutter, which falls when the water rises to a certain height. It has hydraulic brakes at the back to break the shock as the gate rises. In the background is a front shutter, erect, holding up 10 feet of water. large is not easily realized. The river Thames, when it overflows its banks and floods the adjacent country, swirling ThcanaT*3!5 ^rouS^ badges in a torrent and inundating some of the valley towns, carries about 10,000 cubic feet per second. The Chenab Canal, when doing its utmost, but so silently and peacefully as to look placid as compared with the rushing, hurrying Thames, carries 11,000 cubic feet per second—that is, mor© than the Thames in its angriest mood. The canal is 250 feet wide at the base, and when full has a depth of 11 feet. These are the dimensions at tho head. From that point the channels taper down, spreading and branching here and there, until they are reduced to ditches perhaps only 18 inches or a foot wide at the base. The whole system comprises some 2,800 miles of chan- nels, spreading, like the veins of a man’s hand, over a tract of country little less than 4,650 square miles in extent—almost one-tenth the area of England, and half the cultivated area of Egypt. This large area was all Crown waste land jungle What Canal done. the has before the canal was made. A part, well wooded, with three or four kinds of growth, bore a good crop of grass after a favourable rain; and on this nomadic tribes, the only inhabitants, pastured their cattle at certain times of the year. A small scrub and camel thorn covered some of the land. By far the larger portion was abso- lutely barren, a country of mirages which often deceived the engineers. Into such a region 400 miles of main canals and about 1,400 miles of distributaries now conduct the volume of water mentioned above. The main canals and the branches run on the main ridges, and the larger distributaries— some of considerable size, and passing 500 cubic feet a second—keep to the main water- sheds. Two million acres of crops now grow annually on the lands which once were waste and sterile. As the tract irrigated by the Chenab Canal was originally uninhabited, villages had to be formed and settlers introduced. The special colonization, officer appointed had to survey his vast estate, and lay it out in villages and in holdings of convenient size. The system adopted was to divide the whole district into squares of 25 or 27 acres, each square having its individual supply of irrigation water. HYDRAULIC WEIH: BOTH SHUTTERS DOWN.