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<br />e.." <br />I-'- <br />W <br />0) <br /> <br />CHAPTER II. SALINITY OF THE RIVER <br /> <br />. <br /> <br />The Colorado River system drains 244,000 square miles of the western <br />United States and a small portion of northern Mexico. Its waters serve some <br />2.25 mill ion people within the United States portion of the Basin and through <br />export provide full or supplemental water supply to another 12 million <br />people. The regional economy is based on irrigated agriculture, livestock <br />gra2:ing, mining, forestry, manufacturing, oil and gas production, and tourism. <br /> <br />About 2.5 million acres are irrigated within the Basin and hundreds of <br /> <br />thousands of acres are irrigated by waters exported from the Basin. The <br /> <br />Colorado River also serves about 1.5 million people and 425,000 irrigated <br /> <br />acres in Mexico. <br /> <br />Salinity has long been recogni2:ed as one of the major problems of the <br /> <br /> <br />river. The Colorado, like most western rivers, increases in salinity from <br /> <br />. <br /> <br />its headwaters to its mouth. This is the result of both natural and manm~de <br />causes. Natural causes include salt contribution of sal ine springs and other <br />ground waters, erosion and solution of sediments, and the concentrating <br />effects of evaporation and transpiration. Man-caused increases in salinity <br /> <br />result from the diversion, consumptive use,out-of-basin exports of water, <br /> <br />and salt loading. The largest man-induced increase in salinity is caused by <br /> <br /> <br />the concentrating effect of, and salt loading associated with, irrigated <br /> <br /> <br />agriculture. <br /> <br />In addition to the comprehensive studies conducted by the Forum in 1975, <br />1978, and for this review, evaluations of the sal inity of the Colorado <br />River have been made by the Bureau, U.S. Geological Survey (USGS), EPA, <br />Bureau of Land Management (BLM), and the Colorado River Board of California <br /> <br />(CRBC). <br /> <br />. <br /> <br />6 <br />