120 IRRIGATION FAKMIXU. 



A cubic foot of fresh \vatur weighs G2.5 pounds and 

 contains 1,728 inches or 7.5 gallons. 



27,14-4 gallons of water will cover one acre one inch 

 deep. 



'.' 2~> gallons a minute or 25 miner's inches will be 

 sufficient to cover one acre one inch deep in two hours 

 and one minute. 



A simple method to determine what a windmill 

 pump is discharging is to measure the actual dclivcry 

 wich a gallon measure for one minute and multiply by 

 sixty. Divide the gallons per hour by 38 to obtain the 

 acre inches per month, or by 13 for the acre inches in 

 three months. These results arc not mathematically 

 accurate, but will be found close enough for ordinary 

 computations. They make no allowance for seepage and 

 evaporation. 



A safe rule for finding the capacity of a cylindrical 

 cistern is to take the dimensions in inches, square the 

 diameter, multiply by the depth, and then by .0034, 

 which will give the contents in United States standard 

 gallons. Thus to find the capacity of a cistern twenty- 

 five feet in diameter and one foot deep, multiply : 300 

 x 12 x .0034=3672 United States standard gallons. 



To measure flowing water in ditches, canals and 

 rivers, multiply the area by the mean velocity of its flow 

 in feet per second, and the product is the volume in 

 cubic feet; divide the number of cubic feet by 1.57, and 

 the result will be the number of miner's inches. 



