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<br />l7 <br /> <br /> <br />w <br />w <br />o <br />N <br /> <br />in developing a simulation model of the hydrologic and salinity <br /> <br />flow systems of the Upper Colorado River Basin. Estimates were <br /> <br />derived based on the 1931-1960 period and reflect cropping and <br /> <br />riverflow regulation conditions as of 1960. The estimated salt <br /> <br />load at Lees Ferry was 8.6 million tons per year of which approx- <br /> <br />imately 4.3 million tons originated from natural sources, 1.5 mil- <br /> <br />lion tons from within the agricultural system, and 2.8.million tons <br /> <br />from other inputs to the system; thus, natural sources are thought <br /> <br />to contribute SO percent of the salt load, agricultural sources <br /> <br />17 percent, and unidentified sources 33 percent. The report states <br /> <br />that the agricultural salt load and cropland consumptive use <br /> <br />increase the total dissolved solids concentration within the Upper <br /> <br />Basin by 104 and 113 mg/l, respectively. The model was designed <br /> <br />to predict the effects of various possible water resource manage- <br /> <br />ment alternatives. <br /> <br />Salinity of Surface Water in the Lower Colorado River- <br /> <br />Salton Sea Area (USGS) <br /> <br />U.S. Geological Survey Professional Paper 486-E, entitled "Salinity <br /> <br />of Surface Water in the Lo\~er Colorado River-Salton Sea Area," \~as <br /> <br />published in 1971. The report shows that during the period 1926- <br /> <br />1962, the chemical regimen of the Colorado River at Grand Canyon <br /> <br />and ~stream, although probably somewhat different from the virgin <br /> <br />regimen, was relatively stable. There may, however, have been <br />