IRRIGATION IN INDIA AND 

 AMERICA. 



BY. E. H. PARGITER, OF THE IRRIGATION BRANCH, PUBLIC WORKS 

 DEPARTMENT, PANJAB. INDIA. 



(Continued from last month.) 



The physical configuration of a country to be traversed by a canal 

 naturally influences the design of the canal, and usually determines 

 the limits of its size. In the great and almost level plains of North 

 India, there is practically no limit to the width possible, as far as the 

 natnre of the ground is concerned. There the width and discharge 

 are determined, in most cases, by the quantity of water available in 

 the river suplying a canal; if the whole of the low cold weather dis- 

 charge of the river can be utilized for irrigation, then the canal is de- 

 signed to take this discharge, and is given a suitable maximum bed 

 width and minimum depth of supply for it; bearing in mind also that 

 this width, with a greater depth of supply, shall allow of double or 

 even perhaps treble that discharge being taken during the hot 

 weather when the supply in the river is many times greater. The 

 depth of supply possible to be taken in safety in a canal constructed 

 to allow of free flow or gravity irrigation, with its minimum cold 

 weather discharge, thus limits its maximum discharge during the hot 

 weather, and of course it would not be practicable to take, asa rule, 

 more than double the depth of the low supply, consistently with the 

 safety of the banks, and reasonable economy in iconstruction and 

 maintenance. 



In some cases, as in the Jhelam canal now under construction, 

 the small size of the doab to be irrigated, limits the area of land for 

 which water is to be provided; and all the available cold weather dis- 

 charge of the river is not needed. In such cases, the canal is de- 

 signed to take only as much as it needs; and there is no necessity to 

 allow for largely different hot and cold weather discharges; though, as 

 a matter of fact, with approximately equal areas to be irrigated in the 

 two seasons, a considerably larger supply will be required in the hot 

 weather, owing to the greater loss by evaporation, and the greater 

 quantity of water required by the crops then grown. 



The almost level plains of North India allow of curves of great 

 radius being given to a canal; so that a canal with a bed width of 250 

 feet or more, a depth of supply of 10 or 12 feet, and a discharge of 



