66 



THE IRRIGATION AOL. 



of square inches in the opening. The assumption made that the dis- 

 charge is proportional to the size of the opening is not true, but the 

 error in measuring small quantities is not great enough to be taken 

 into consideration. By converting the results of measurements in 

 miner's inches to gallons, cubic feet, or some other familiar unit, it 





FIG. 2. Measurement of a brook by the miner's inch method. 



may be determined how long it will take the stream to fill a reservoi r 

 or cover a given field with the necessary depth of water. This unit is 

 readily convertible into cubic feet or gallons or acre inches of water, 

 according to the time the water flows. 



The following data will be helpful in computations: One miner's 

 inch, as described above equals 0.1496 gallon per second; 8.976 gallons 

 per minute; 538.56 gallons per hour; 12,925.44 gallons per day; 0.02 

 cubic foot per second; 1.2 cubic feet per minute; 72 cubic feet per 

 hour. One acre inch of water (that is; 1 inch in depth over an acre of 

 surface) equals 27,152 gallons, or 3,630 cubic feet, and 1 miner's inch 

 will supply this quantitj r in about 50.4 hours. Thus a simple calcula- 

 tion shows that a little stream of 5 miners inches will supply enough 

 water to cover an acre 2.3 inches deep in about 23 hours a fair amount 

 for one irrigation of soil of average character if it has not been allowed 

 to become too dry before the application; 1 in fact, this is an average 

 amount actually used for an irrigation of shallow- rooted plants like 

 most field and garden crops. 



SOURCES OF WATER SUPPLY AND THEIR USE. 



The sources of water supply and methods of use most frequently 

 available for a single farm include the following: Diversion of peren- 

 nial streams; development in dry stream beds; development of springs 



*For the water capacity of different soils see U. S. Dept. Agr., Farmers' Bui. 46i 

 p. 14. 



