Salinity Problems in the Lower Colorado River Area

Document: State of California, Colorado River Board of California, "Salinity Problems in the Lower Colorado River Area," September, 1962, page 17MEXICALI VALLEY The history of irrigation in Mexicali Valley is contemporaneous with that of the Imperial Valley. The right to divert up to one-half the water flowing in the Alamo Canal was reserved to irrigate Mexican lands in return for the concession by the Mexican Government to predecessors of the Imperial Irrigation District of the right to convey Colorado River water in the canal through Mexican territory. In 1920, 220,000 acres were irrigated in Mexico and in 1942, at the completion of the All-American Canal, 260,000 acres. Ratification of the 1944 Treaty, with its guarantee of minimum annual quantities of water at regulated rates resulted in a large increase in irrigated acreage; it reached a maximum of more than 500,000 acres in 1957, and is reported to be 410,000 acres in 1962. Water for irrigation of the land west of the Colorado River is diverted from the river at Morelos Dam a mile below the California-Mexican boundary and conveyed through the Alamo Canal and branches thereof. In addition, about 500,000 acre-feet a year of ground water is pumped into the canals from wells in the eastern portion of the area. Mineral content of the ground water is said to average about 1,400 ppm. Waste and drainage water from the Yuma Valley Project is taken across the land boundary at San Luis into a canal system which serves lands in Sonora, east of the Colorado River. In addition a number of diversions are made by pumping directly from the river. It is reported that all but one of these pumped diversions will be replaced upon completion of a siphon now under construction to convey water from the Alamo Canal under the river to the east side. Substantial quantities of waste water from the Alamo Canal and drainage and domestic sewage from Mexicali Valley re-enter the United States in the channels of the New and Alamo Rivers. Little adequate drainage has been provided in the Valley however. The soils are generally tight and because of the lack of adequate drainage the salts in the irrigation water have accumulated in the soils to the extent that serious problems of soil salinity exist in many parts of the Valley. Thus the problem in the Mexicali Valley has been building up over the past half century by failure to achieve a favorable salt balance in the soils. The beginning of the highly salinized outflow from the Wellton-Mohawk area has simply aggravated the problem into an acute status. Crops grown in Mexicali Valley are largely cotton and winter wheat. In 1961 over 70 percent of the crop land was planted to cotton. For this reason, and because the water requirement of winter wheat is comparatively small, the demand for water for irrigation is high in the summer and relatively low in the winter. [17] 2-74889Epson Perfection 4870 Photo, 600 dpi, 8 bit, 3,892,348 byte