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<br />~ <br />Q) <br />rv <br />.....:t <br /> <br />Long-term historical flow and salinity conditions for the Colorado River <br />at Imperial Dam are depicted in Figures VIII-2 and VIII-3, respectively. <br />Figure VIII-2 shows the amount of water that reached Imperial Dam in the years <br />1983-85 was unusually high compared to the last 2 decades. Since the 1966 <br />closure of Glen Canyon Dam, with few exceptions, flows at Imperial Dam have <br />fluctuated within the narrow range of 5 to 6 million acre-feet, primarily due <br />to the filling of Lake Powell (1963-80) and the ability to control the <br />releases from the Upper Basin with the storage available in Lake Powell. With <br />Lake Powell at near capacity, more water has been released, reducing the <br />salinity in the Lower Basin. <br /> <br />The additional water in 1980, 1983, 1984, 1985, and 1986 had a dramatic <br />dilution effect on the salinity concentrations at Imperial Dam. Figure VIII-3 <br />shows an average annual value of 607 mgIL in 1985, the lowest level of the <br />period 1941-85. It appears that the 1986 salinity level will be even lower <br />than the 1985 value. <br /> <br />The 1986 salinity levels at Imperial Dam were again due to excess flow <br />and are expected to have a continuing but temporary impact on future salinity <br />projections. Due to the flushing out of more saline water in the major <br />reservoirs, current salinity reductions will also have a short-term impact on <br />salinity projections but will have little impact on long-term projections. <br />Reclamation estimates that normal flows would increase the salinity levels <br />back to the 800 mgIL range in 6 to 7 years. <br /> <br />The base condition from which all salinity projections are made assumes a <br />starting salinity condition at present 1986 levels, existing levels of <br />development as a starting point, scheduled developments for predictions in the <br />future, and existing salinity control units operating at existing levels <br />(126,800 tons per year). <br /> <br />The base condition for the evaluation assumes that no more funds would be <br />expended on salinity control after FY 1986. Consequently, only the completed <br />salinity control units or portions of units shown below are considered in the <br />base: <br /> <br />Table VIII-l. Existing salinity control unit summary. <br /> <br />Tons/year Removed <br />Uni t as of 1985 <br /> <br />Grand Valley Stage One (Reclamation) <br />Grand Valley (USDA) <br />Meeker Dome (Reclamation) <br />Uinta (USDA) <br />Las Vegas Wash (Pittman Bypass) <br />BLM well plugging <br />Total <br /> <br />21,900 <br />27,300 <br />48,000 <br />15,600 <br />7,000 <br />7,000 <br />126,800 <br /> <br />VIII-2 <br />