PROBLEMS FROM LAND OCCUPANCY 199 



Studies have shown, however, that the effect of the reser- 

 voir extends only a short distance beyond its boundaries. 

 Other studies show that the real culprit is probably the 

 artesian reservoir. Under most of the valley floor, water in 

 sand and gravel strata is confined under artesian pressure 

 by a layer of clay less than 50 feet thick in many places. This 

 clay permits some upward movement of water from the 

 aquifer, and the rising water accumulates in the soil and 

 even on the surface until it is dissipated by evapotranspira- 

 tion. Experimental pumping in 1930 from a well tapping 

 the artesian reservoir proved that waterlogging can be 

 eliminated by lowering the artesian pressure sufficiently, 

 but none of the waterlogged land has yet been reclaimed by 

 this method. 



Imperial Valley, Calif.™ The Colorado River has dis- 

 charged intermittently into this trough-like valley for mil- 

 lions of years and has contributed sediments that are now 

 thousands of feet thick. These sediments are clay, silt, and 

 sand of low permeability, with no known gravel layers of 

 any considerable extent, and there is practically no irriga- 

 tion from wells. The extensive agricultural areas are irri- 

 gated with Colorado River water brought in by the Alamo 

 and All- American Canals. The ground-water problems are 

 those of waterlogging and salt accumulation in the soil, 

 resulting from high water table. By October 1947, drainage 

 had been provided for 45,000 acres within the Imperial 

 Irrigation District; 1,5.00 miles of open drains were con- 

 structed to avoid the areas of highly plastic and impervious 

 clay, and 1,000 miles of tile drains were installed in the most 

 pervious layers. 



In an average year the water imported for irrigation 

 brings in about 2,600,000 tons of salt, and the drains carry 

 out about 2,300,000 tons. More than 300,000 tons of salt 



34 Reference: Aronovici, V. S., W. W. Fox, and W. W. Donnan, "Imperial 

 Valley Drainage Investigation," U.S. Soil Cons. Service, 

 Progress rept., 1944. 



