IRRIGATION 



259 



according as more or less water is being drawn above 

 the orifice. The amount of water let through under the 

 constant head is regulated by the slide A shown in 

 Figure 153. 



An acre inch means sufficient water to cover an acre 

 of land an inch deep, and is 226,875 pounds, 28,359 

 gallons, or 886 barrels of 32 gallons each. 



Constructing farm supply ditches and field ditches. 

 The location and construction of ditches to carry the 

 water to the fields can be done with the reversible road 

 machine, Fresno scraper, especially devised scrapers, the 



Figure 155. Showing plank scraper in use, placing the embankment all on one side 

 of the ditch. 



road plow, the common stubble plow, the spade and 

 other suitable implements. In many cases the earth 

 from the ditch can be made to serve as an embankment 

 in checking ofT nearly level fields or in terracing the hill- 

 sides with slight fall so as to hold water in flooding. 



Locating field laterals. In making shallow laterals 

 through the farm, and often temporary ditches through 

 the fields, it is necessary to curve about small eleva- 

 tions so as to have only very slight grade to the 

 ditches. 



