362 THE IRRIQA110N AGE. 



far in excess of what is required for irrigation. During the cold 

 weather less water is required, and the whole supply of a river is 

 often dammed up. at the weir and taken into the canal or canals taking 

 out of the river above its weir. 



As, however, the beds of the rivers are pure sand to a great 

 depth, there is a large underflow below each weir, and this comes out 

 on to the river bed again at some distance downstream, again forming 

 a flowing river, though of greatly diminished volume. 



In years of drought, when the rains in the plains fail, the rainfall 

 in the Himalaya mountains, though very much less than usual, is still 

 always in sufficient quantity to make the rivers rise and give them a 

 fairly good supply, more than enough to fill to their fullest capacities 

 all the canals at present constructed and supplied from them. Hence 

 the first canal along a river never suffers from want of water during 

 the rainy season; others lower down its course, where there are no 

 weirs to raise and impound the water, may receive a less supply than 

 usual owing to the river level being lower than in years of good rain- 

 fall, but the river supply is not all utilized. Such canals are small 

 and occur in series and will be described further on as Inundation 

 Canals. A weir cannot be provided for each one, as the cost would be 

 out of all proportion to the benefit to be gained, and is absolutely pro- 

 hibitive. But the question of amalgamating a series of these canals 

 and giving them all one head with a weir in the river, is now coming 

 under consideration in the Irrigation Department of the Panjab as a 

 practical scheme, 



(TO BE CONTINUED.) 



