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<br /> <br />Salini ty concentrations at Imperial Dam decreased steadily <br />from 1970-79, increased in 1981-82, and decreased significantly <br />W from 1983-86. The period 1983 through 1986 was a period of above- <br />-...] normal runoff. Each of the four years had an estimated natural <br />~ flow in excess of 20.0 million acre-feet (maf), with the four year <br />W average of 22.6 maf. Only one other period has had 20 maf of <br />natural flow for two or more consecutive years (1920-21), and only <br />one period (1920-23) had an estimated average natural flow <br />exceeding 20.0 maf (20.4 maf). During 1983-86, the annual calendar <br />year flow to Mexico exceeded scheduled deliveries by 12.6, 13.8, <br />10.1, and 9.2 maf, respectively, for a total of 45.7 maf. <br /> <br />The record high flows during the period 1983-86 produced a <br />significant reduction in salinity concentrations in the lower main <br />stem by approximately 250 mg/l at Imperial Dam. With river flows <br />dropping below normal since 1987, salinity concentrations are <br />increasing. However, because of the large volume of lower salinity <br />water in the reservoirs, the rate of increase has been attenuated. <br /> <br />The flow-weighted average annual salinity at the stations for <br />which numeric criteria have been set are shown in Table 2. <br /> <br />Projections of Future Water Depletions <br /> <br />One of the significant factors affecting salinity <br />concentrations is water use. Estimates of both 1989 water use and <br />projected future use through the year 2010 for each of the seven <br />states were developed jointly by the states and Reciamation. <br /> <br />Table 3 presents a summary of projected water depletion in the <br />Upper Colorado River basin, and from the main stem of the Lower <br />Colorado River. Figure 2 presents the total water depletion. <br /> <br />Salt Routing Studies <br /> <br />Salt routing studies were made for the 1990 Review using the <br />Colorado River Simulation System (CRSS) developed by Reclamation.2 <br />The CRSS is a package of computer programs and databases developed <br />by Reclamation as a tool for use by water resource managers dealing <br />with water related issues and problems in the Colorado River basin. <br />The central feature of the CRSS is a computer program which <br />simulates the flow of water and salt through the system and the <br />operation of the reservoirs including hydroelectric power plants. <br /> <br />2 <br /> <br />Detailed information on CRSS is presented in the following <br />Bureau of Reclamation reports: Colorado River Simulation <br />System, An Executive Summary (October 1981); Colorado River <br />Simulation System, Users Manual (June 1982); and Colorado <br />River Simulation System, System Overview (1984). <br /> <br />9 <br />