394 THE IRRIGATION AGE. 



and has been working for more than thirty years, though some of its 

 branches were not ready till much later; then the Sirhind Canal from 

 the River Satlej was taken in hand, and has been working for seven- 

 teen years; and next the Chanab Uanal from the River Chanab, just 

 completed, though some branches have been working for several 

 years- The next canal to be opened will be the Jhelam Canal, from 

 the River Jhelam. This has been lately commenced, about three 

 years ago, and is expected to take five or six years in construction 

 from its commencement, before it will be sufficiently ready to be 

 opened for irrigation. 



The circumstances and designs of the first named of the above 

 canals, are very similar, and show the site on a river that engineers in 

 India 30 years ago considered it necessary to select for the head works 

 of a large perennial canal. This site is the point where the river 

 leaves the lowest mountain ranges, and enters the great plain of 

 North India. Here the river bed is permanent, and narrower than in 

 its course further down through the great alluvial plains in which, as 

 the river when in flood erodes its banks to a large extent, a very wide 

 bed has been cut in the course of centuries. The wier or dam across 

 the river at the site selected, would be shorter than further down, 

 while there is always an abundance of good building stone in the 

 mountains close by, and the river bed is full of boulders of all sizes, 

 admirably adapted for paving and flooring, and pitching (or riprapp- 

 ing) the sides of works and channels. 



The disadvantage of such a site for the head of a canal, are, 

 firstly, that for the first few miles of its course the canal is in very 

 deep digging, and the cost of the large quantity of earthwork in ex- 

 cavation is considerable; and secondly, that the canal has to cross 

 several hill torrent and drainage channels that fall into the river. 

 The crossings are very troublesome and expensive to construct; and 

 the subsequent training of the torrent channels leading to and from 

 the crossings, needs constant attention and frequently a heavy ex- 

 penditure on spurs and riprapping. These channels are usually dry, 

 except immediately after heavy rain, when they are filled with a rush- 

 ing, raging flood of water, the drainage from the lowest range of hills 

 to the river. This water is heavily laden with sand and sediment, 

 and cannot be taken into the canal for fear of choking it up with the 

 sediment that would then be deposited. Also the amount of water 

 brought down would often be much in excess of the capacity of the 

 canal. Hence each drainage channel of any considerable size must be 

 provided with a syphon crossing, to pass it under the bed of the canal; 

 or with a super-passage, to pass it above, wherever the canal is in 

 such deep digging that the bed of the torrent is well above the full 

 supply level in the canal. The foundations of these syphons and 



