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<br />C,)1 <br /> <br />The Forum adopted a system of baseline salinity values for certain key monitoring points <br />in 1980. Since that time salinity changes at these baseline stations have been separately reported <br />and commented upon in subsequent triennial reviews. The Forum has not found the concept of <br />baseline values to be especially helpful in guiding salinity control efforts, and as of this 1993 <br />Review, will not be relying on the notion of baseline values to assess or plan the program. <br /> <br /> <br />and coliform. In addition, continuous recordings of temperature and specific conductance are <br />taken at seven stations in Utah. <br /> <br />OBSERVED SALINITY CONr.F.NTRATlONS <br /> <br />Salinity concentrations of the river have fluctuated significantly over the period of record, <br />(1941-1991; Figure 2.2). Salinity concentrations generally decrease in periods of high flows and <br />increase in periods of low flows. Figure 2.2 shows the inverse relationship between the mean <br />annual flow and the salinity of the Colorado River at Imperial Dam. <br /> <br />Salinity concentrations at Imperial Dam decreased steadily from 1972-1979, increased <br />in 1981-1982, and decreased significantly from 1983-1986. The period 1983 through 1986 was <br />a period of above-normal runoff. Each of the four years had an estimated natural flow at Lee <br />Ferry in excess of 20.0 million acre-feet (mat), with the four year average of 22.6 maf. Only <br />one other period has had 20 maf of natural flow for two or more consecutive years (1920-1921), <br />and only one period (1920-1923) had an estimated average natural flow exceeding 20.0 maf <br />(20.4 mat). During 1983-1986, the annual (calendar year) flow to Mexico exceeded scheduled <br />deliveries by a cumulative total of 45.7 maf. <br /> <br />The record high flows during the period 1983-1986 produced a reduction in salinity <br />concentrations in the lower main stem of approximately 250 mg/L at Imperial Dam. Table 2.1 <br />(page 2-6) shows the flow-weighted average annual salinity concentrations from 1972 to 1992 <br />at Imperial Dam and also below Hoover and Parker Dams. With river flows below normal from <br />1987 to 1992, salinity concentrations increased. Initially, because of the large volume of lower <br />salinity water in the reservoirs, the rate of increase was attenuated. However, as of 1992, the <br />reservoirs had been drawn down and most of the lower salinity storage water had already been <br />released. <br /> <br />WATER USE AND AsSQCIATED lMPACfS OF SALINITY <br /> <br />The Colorado River, from its headwaters in the Rocky Mountains to its mouth in the Gulf <br />of California, is utilized for a variety of purposes. A portion of the flow is transported out of <br />the Colorado River Basin for use in adjacent river basins. In the Colorado River Basin, <br />irrigation, municipal and industrial, powerplant cooling, fish and wildlife, and recreation are the <br />major uses of the river water. <br /> <br />Colorado River water users in the Lower Basin have suffered significant economic <br />impacts due to long-term continued use of water with elevated salinity levels. Figure 2.3 on <br /> <br />2-4 <br />