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<br />STORAGE CHANGES <br /> <br />Upper and Lower Basin reservoir storage increased from 1972 <br />through 1983, and began declining in 1987. By 1991, the storage <br />C) had declined sharply. As shown on Figures 1 and lA, basinwide <br />~ storage at the end of Calendar Year 1991 was about 12.6 maf less <br />~ than at the end of 1987. Of the total difference, 7.6 maf was in <br />~ the Upper Basin and 5.0 maf was in the Lower Basin. The 1991 end <br />of calendar year storage in the Colorado River system was about 1.5 <br />million acre-feet less than the 1990 value. <br /> <br />During 1990 storage in most of the major reservoirs on the <br />Colorado River declined and only flows required to meet downstream <br />demands were released. The reduced flows in 1988 thru 1991 have <br />resulted in an increase in salinity concentrations in the major <br />reservoirs. <br /> <br />HISTORICAL USES <br /> <br />Estimated historical Lower Basin mainstream and Upper Basin <br />uses for calendar years 1975 through 1990 are shown in Table 2. <br /> <br />SALINITY CONCENTRATION AT MONITORING STATIONS <br /> <br />salinity concentrations for the years 1973-1990 at the three <br />stations at which numeric criteria have been set (below Hoover Dam, <br />below Parker Dam, and at Imperial Dam) are shown in Table 3. These <br />concentrations are all less than the numeric criteria. <br /> <br />TABLE 3 <br />FLOW-WEIGHTED AVERAGE ANNUAL SALINITY CONCENTRATIONS <br /> <br />AT SELECTED STATIONS <br />(Total Dissolved Solids in <br />Calendar Below Hoover Below Parker <br /> <br />Nume~~~rcriteria ~~ ~ <br />1973 709 <br />1974 681 702 <br />1975 680 702 <br />1976 674 690 <br />1977 665 687 <br />1978 678 688 <br />1979 688 701 <br />1980 691 712 <br />1981 681 716 <br />1982 679 713 <br />1983 658 678 <br />1984 598 611 <br />1985 556 561 <br />1986. __ 517 ' - 535 <br />1987 519. 538 <br />1988 529 540 <br />1989 564** 559** <br />1990 578** 600** <br /> <br />mg/l*) <br />At Imperial <br /> <br />~ <br /> <br />834 <br />829 <br />822 <br />819 <br />812 <br />802 <br />760 <br />821 <br />827 <br />727 <br />675 <br />615 <br />577 <br />612 <br />648 <br />683** <br />702** <br /> <br />*Determined cooperatively by the U.S. Geological Survey (USGS) and <br />Reclamation. Published in "Quality of Water - Colorado River <br />Basin," Progress Report No. 15, January 1991. Some of these values <br />have been revised from previous years. <br />**provisional records. <br /> <br />3 <br /> <br />,,;> <br />