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SALINITY PROBLEMS-LOWER COLORADO RIVER 19 According to the handbook, study of more than 1,300 sources of irrigation water indicates that less than 10 percent of the samples were in the very high salinity range (1,350 to 3,000 ppm). The Imperial Irrigation District, California, provides a prime example of the profitable irrigation of fine-textured soils of poor natural drainage with water which on the basis of data in Handbook 60 is "high salinity water." Records by the Imperial Irrigation District, from 1944 through 1955, show a salt content of water in the All-American Canal varying from about 680 to 860 ppm (0.93 to 1.17 tons per acre-foot of water). Geographically and geologically, the Imperial and Mexicali Valleys are one. Imperial Valley farmers initially faced the same problems which now confront the Mexicans, but the Imperial Valley farmers leached their soils and installed extensive drainage facilities to avoid excessive salt accumulations. The soil in Imperial Valley is complex, with no particular pattern or soil profile. By 1922 substantial areas in the valley had gone out of production because of drainage and salinity problems. Starting then, drain ditches and subsequently tile drains were constructed and the systems have been extended every year. In the period of record, since 1943, the salt content of the water discharged from the District into the Salton Sea varied from 2.03 to 3.42 tons per acre-foot. The gain in removal of salt from 1949 to 1955 inclusive was about 1 3/4 million tons. In contrast, it is said that the struggle against soil salinity and alkalinity in the Mexicali Valley has always been and still is losing ground. Authorities state that even without the incidence of the Wellton-Mohawk drainage channel effluent, users in the Mexicali Valley would still face a salinity problem because of the lack of adequate drainage facilities. The Mexicans themselves have recognized that a part of the problem is attributable to the need for drainage and better irrigation practices. Nevertheless the Mexicali Valley farmers have overextended their irrigated area by planting more acreage than can be irrigated and drained properly with the available water supply. It is reported that although the Mexicali Valley now has about 900 miles of open drain ditches, it has need for at least 900 miles more ditches and for extensive tile draining of farmlands. No tile drains exist now. Also the water distribution system is said to be badly in need of rehabilitation and improvement to reduce the loss of water to seepage and non-beneficial plant growth.Epson Perfection 4870 Photo, 400 dpi, 24 bit, 9,944,064 byte