FARM IRRIGATION 251 



the grooves should be tight so that no water will 

 trickle through; sometimes they are faced with 

 rubber or leather. Besides many styles of these 

 home-made gates there are various manufactured 

 gates which are more complicated. 



Distributing Ditches and Flumes. Having 

 brought the water to the farm by ditch, flume or 

 pipe, it must now be distributed to different fields. 

 This is usually done by taking out from the main- 

 supply ditch smaller distributing ditches or laterals, 

 which should have a slight but uniform grade. 

 Generally it is best to run these main laterals direct 

 to the different fields, from the point where the 

 water is delivered, and to take from them small 

 laterals to all parts of the fields. The main lateral 

 or " head-ditch," is located on the border of the 

 fields, if the land is nearly level; or on the ridges, 

 without regard to field lines, if the land is rolling. 

 They are usually permanent. Laterals for flooding 

 should be 50 to 100 feet apart. Laterals for furrow 

 irrigation are farther apart, usually from 20 to 50 

 rods and run across the direction of the furrows, 

 so that water can be turned into each furrow at its 

 head. These small laterals may be permanent or 

 temporary. Distributing laterals should be run 

 nearly at right angles to the greatest slope of the 

 land. A fall of at least five feet per mile is com- 

 monly recommended and twenty-five to thirty feet 

 per mile is not uncommon. 



Small laterals are quickly built with a mould- 

 board plow by turning up two parallel furrow- 

 slices with unbroken ground between them. The 

 bottom of the ditch should be on a level with the 

 surface outside, so that water will flow out of it 

 when the bank is cut. In other words the banks 

 must be made of soil that is mostly taken from 



