PROBLEMS FROM LAND OCCUPANCY 197 



tion projects the corrective measures were undertaken only 

 after the need for them was shown by the loss of production 

 from certain lands. As almost every project for irrigation by 

 surface water is likely to create problems of rising water table 

 eventually, the probable needs for drainage have become an 

 essential part of preliminary project investigation and plan- 

 ning. 



The magnitude of the requirements for drainage in irri- 

 gated western valleys is suggested by the conditions in San 

 Joaquin Valley, Calif, (page 70), where by 1940 some 505,- 

 000 acres in a total irrigated area of 749,000 acres had been 

 provided with drainage. 32 The preferred type of drainage 

 is by pumping from wells, because wells can be placed where 

 drainage is needed and can lower the water table to greater 

 depths than can be done by any other method. In the Tur- 

 lock irrigation district, for instance, the increase of water- 

 logging and alkalinity reached alarming proportions early in 

 the century, and open drains excavated about 1920 did not help 

 much. Beginning in 1924, the district started to pump from 

 wells for drainage. By 1943 about 155,000 acre-feet was pumped 

 annually, of which 120,000 was used for irrigation elsewhere 

 in the district. The drainage pumps are operated so as to 

 maintain the water table at a fixed depth of about 6 feet. In 

 some valleys the use of wells for drainage has provided water 

 so valuable for irrigation that pumpage has been expanded 

 for additional supplies and lowered the water table signifi- 

 cantly. 



In the very permeable soils of the west slope of San Luis 

 Valley, Colo, (page 87), the farmers have found it possible to 

 regulate the position of the water table by adjusting the water 

 levels in ditches, which thus have become combination irri- 

 gation and drain ditches. Water reaches the crops by subirriga- 

 tion and need not be distributed over the fields. By contrast, 

 in Cache Valley, Utah, experiments have shown that water- 

 logging of the clayey soils in the lower parts of the valley is 



32 Ewing, P. A., "Irrigation and Drainage in San Joaquin Valley, Calif.," 

 U.S. Soil Cons. Service, Mimeo rept., p. 54, 1946. 



