IRRIGATION AND DRAINAGE 



147 



Fig. 69. Ridger used in basin irrigation 



with steel, which extends part way up the inner side. The runners 

 are 4 or 5 feet apart at the front end and from 16 to 24 inches at 

 the rear, and are held in position by the crosspieces on top, by a 

 floor, and by straps of steel. The height of the ridges varies with 



depth of water to be ap- 

 plied, from 4 to 9 inches; 

 their elevation above the 

 surface of the water when 

 a basin is flooded should 

 be several inches. 



Several methods of 

 flooding basins are prac- 

 ticed. In one a ditch is 

 run from the supply ditch 

 at the head through alter- 

 nate row spaces, so that the basins on each side are flooded in 

 pairs, beginning with the lowest. This plan is shown in outline 

 in Fig. 70. In another method water is allowed to flow through 

 openings into each basin of a tier in a zigzag course from the top 

 to the bottom of the or- 

 chard, the upper basins 

 receiving the most water. 

 With gravity canals, 

 where water is abun- 

 dant, the water is turned 

 into the upper basin un- 

 til it is full and overflows 

 into the next, and so on 

 down the tier. The irri- 

 gator then begins at the 

 lower end and repairs 

 the breaks, leaving each 

 basin full of water. 



The check method. Where the check method is practiced, it 

 frequently happens that the land planted to fruit trees is that on 

 which alfalfa has been grown. In plowing down the alfalfa and 

 setting out the trees, the levees undergo little change and the checks 

 can be flooded if it is considered best. A better plan is to furrow 



Fig. 70. Basin method of irrigation 



