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<br />-4- <br /> <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br />I <br /> <br />In the western portions, many of the mountain streams remain pristine and <br /> <br />pollution free. Sediment and naturally occurring dissolved solids are major <br />problems in the rivers crossing the plains. Where land is cultivated, return <br />flows from the croplands are often laden with fertilizers, pesticides, and <br />herbicides degrading nearby watercourses. Runoff from animal feedlots and <br />municipal and industrial wastes also causes water-quality problems. The <br />quality of ground water varies between and within aquifers. <br />Water Use--Water for irrigation accounts for about 80 percent of all <br />basinwide water withdrawals from both ground and surface sources. Withdrawals <br />for cooling at steam-electric power plants, predominantly from surface sources, <br />run a distant second--about 10 percent of basin water withdrawals. All other <br />purposes constitute the remaining 10 percent of water withdrawn from ground and <br />surface sources. <br /> <br /> <br />Hydroelectric power generation facilities are a major component of water <br /> <br /> <br />development in the basin. Their installed capacity currently exceeds 3,300 <br /> <br /> <br />megawatts representing over 15 percent of total generating capacity in the <br /> <br /> <br />basin. <br /> <br /> <br />Problems and Needs <br /> <br /> <br />Problems--A number of studies have been conducted in the basin in recent <br /> <br /> <br />years to estimate current and projected water use and availability. Results <br /> <br /> <br />from these studies differ substantially. This is illustrated by a comparison <br /> <br /> <br />of the figures presented in The Missouri River Basin Comprehensive Framework <br /> <br /> <br />Study, published in 1971, and those of the Second National Water Assessment, <br /> <br /> <br />published in 1979. Comparisons of net depletions and average depleted outflows <br /> <br /> <br />under current water-use conditions are presented in table 1. It should be <br /> <br /> <br />recognized that the framework study used 1970 for current conditions, while the <br /> <br /> <br />national assessment used 1975. However, this change in base year does not <br />