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<br />Co" <br />~ BLM-administered public domain lands and other potential onfarm programs have . <br />~ <br />not been taken into account. As more information on these and other salinity <br />control measures becomes available, these measures can be incorporated in <br />future salt routing studies. <br />The policy set forth in the 1975 report calls for maintenance of salinity <br />concentration in the lower main stem of the river at or below the 1972 f1ow- <br /> <br />weighted average annual value while the Basin states continue to develop <br />their compact-apportioned waters although temporary variations may occur as <br /> <br />described in Chapter III. <br />Modifications to Salt Routing Model Input Data <br />A major factor influencing the results of the salt routing analyses is <br />the amount of salt entering the river system under 1979 conditions of devel- <br />opment. When work on the Forum's 1978 report was near completion, it became <br />apparent that the input data to the model used in both the 1975 and 1978 <br /> <br />. <br /> <br />reports to estimate future sa1 inity concentrations gave results that were too <br />high when compared with the most recent information available in 1978. A <br />preliminary investigation indicated that the salt load entering the river <br />system under 1976 levels of development was overestimated by 500,000 to <br />1 million tons per year. Time limitations precluded the reevaluation of <br />salinity projections for the 1978 report; however, the estimated impact of a <br />500,000-ton-per-year salt load reduction on projected salinity levels at <br />Imperial Dam was shown on Figures 2 and 4 of the 1978 report. <br />After completion of the 1978 report, a study was undertaken to develop <br />model inputs which would more accurately reflect present conditions. Inves- <br />tigation was centered on four areas: inflow to Lake Powell, inflow from Lees <br />Ferry to Grand Canyon, salt gain or loss in Lake Powell, and bank storage in <br /> <br />. <br /> <br />Lake Powe 11 . <br /> <br />14 <br />