MACHINERY 3.V 



Duty of water % 

 The duty of water is the irrigation work which a given 

 quantity of water can perform and is usually shown as the 

 number of acres on which a crop can be irrigated by a 

 continuous flow of water at the rate of 1 cubic foot per second. 

 The duty of water when used to cultivate paddy is much less 

 than when irrigated dry crops are grown. For tank irrigation 

 which is generally wasteful, the duty may be taken as 50 

 acres : in large irrigation systems, where the water is under 

 proper control, the duty will be as high as 100 acres. For 

 water lifted from wells by engines and pumps the duty may 

 be taken as 240 acres ; actual experiment at Coimbatore with 

 water lifted from wells gives 280 acres. At Cawnpore where 

 sugarcane needed 50 acre-inches of water, the duty is 171 : 

 for wheat 347 and for maize 192. 



Amounts of water needed for irrigated crop*. 

 (Exclusive of rain-fall.) 



Crop. 



Paddy 



Ragi, monsoon crop 

 Ragi, hot weather 



Cholam 



Sugarcane (Cawnpore) 

 Maize ( do. ) 

 Wheat ( do. ) 



Water data. 



1 cubic foot water — 62425 lb. = '557 cwt. = -028 ton*. 

 1 cubic inch = '03612 lb. 



1 gallon = 10 lb. = 16 eft. = 277*274 cubic inches, 

 1 cubic foot = 625 gallons (6i gallons). 



Gauging water. 



1. Through a sluice or submerged opening 

 Q = A X V=A X5^"H 

 where Q = quantity in cusecs (c. ft. per second). 



A = area in sq. feet of the opening through which th« 



water passes. 

 H = height of water in feet above the centre of the 



opening. 

 Q x 375 = gallons per minute. 



V = Mean velocity of water approaching the opening in 

 feet per second. 



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