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<br />Data collection at these stations include streamflow, specific conductance, and periodic <br />sampling for dissolved solids concentration. In addition to those stations shown in Figure 2-1, <br />many other monitoring stations are maintained where data can, in part, be used to analyze the <br />effectiveness of the salinity control program. <br /> <br />~ <br />o <br />c.o <br />1-. <br /> <br />Observed S~linity <br /> <br />Salinity of the river, and to a lesser extent salt loading, has fluctuated significantly over <br />the period of record (1941-1994; Figure 2-2). Salinity generally decreases in periods of high flow <br />and increases in periods oflow flow as can be seen in Figure 2-2. <br /> <br /> Salinity vs Flow at Imperial Dam <br /> 1000 40 <br />- 820 32 <br />...J 'C' <br />-. >. <br />0) OJ:: <br />E 640 24 co <br />- E <br />~ - <br />&:: 460 16 == <br />(ij 0 <br /> u: <br />CJ) 280 8 <br /> 100 0 <br /> 1940 1955 1970 1985 2000 <br /> Years <br /> FIGURE 2-2 <br /> <br />Record high flows during the mid-1980's resulted in a reduction in salinity in the lower <br />main stem of approximately 250 mg/L at Imperial Dam. Conversely, the period from 1988 to <br />1992 was the driest five years of record historically observed. As a result, storage in the <br />reservoirs was depleted and salinity in the River gradually increased. Table 2-1 shows the flow- <br />weighted salinity from 1972 to 1995 below Hoover and Parker Dams, and at Imperial Dam. <br /> <br />2-4 <br />