Engineering Wonders of the World
Volume III

THE GREAT IRRIGATION WORKS OF INDIA. 241 The engineers had to protect the piers and under sluices from the large stones swept down by the current by sheathing them in sheets of iron. Owing to the lack of that experience which has been gained during the last half century, the engineers made the mistake of placing the head of the Bari Doab Canal too A Beautiful far river. The results Spot. r have been costly, but beautiful. In the first twelve miles of its course the canal drops more than 200 feet by a series of cascades and rapids, and winds between well-wooded banks, protected by stone revet- ting at curves, in a comparatively shallow stream. The velocity of the current is high, and the water sparkles brightly in the sun. It is as pretty a piece of canal scenery as India can show. The river Ganges, which has a course of more than 1,500 miles, and a catchment basin extending over an area more The Ganges r , than seven times the size of Canal. England, is bridled at two points to irrigate the fields of the United Prov- inces. The two systems have quite separate Building Temporary Dams. heads, but meet at a certain point. Together they include 6,500 miles of channels, and irrigate, in some years, more than 2,000,000 acres of crops. The head of the Ganges Canal is at Hurd- war, a very beautiful place, and one of the most holy spots on the most sacred of Indian rivers. The canal works had to be carried out in such a manner as not to affect the sacred bathing places of the Hindus, although a channel passing these spots had to supply the canal. In this very picturesque channel several masonry weirs and escapes have been built to regulate the stream. More interesting is the temporary dam con- structed during the dry season to force the waters of the parent stream to flow down the channel. The first operation in the making of the dam is to fix a 14-inch rope across the river, and to prop it up at intervals so that it hangs in festoons. Triangular cribs are made on the bank out of poles bound strongly together. A barge picks up one of the cribs by means of a derrick hanging over the stern, and is drawn with the help of pulleys run- ning on the main rope into the required posi- tion on the line of the dam. Then the crib is lowered gradually on to the bed of the river, boulders being dropped into it as it descends, so that by the time it is seated its weight suffices to keep it steady. It is then lashed to its neighbour, and weighted with more boulders. This operation is repeated until a line of cribs extends right across the river. All this is done in a stream 8 or 10 feet deep in places, and moving perhaps 12 feet per second. Next, the dam is raised by boulders dropped uniformly vol. nr