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Show Effect of Ultimate Depletions A reservoir operation study was also made for ultimate depletion of 7,500,000 acre feet of water in the Upper Basin. The analysis shows that the salt concentration in the releases from Glen Canyon will increase. Neglecting the modifying factors mentioned on page 5, the salt concentrations will vary between 1.04 and 1.26 and will average about 1.15 tons per acre foot. Base Exchange and Sodium Percentage Base exchange which occurs as a by-product of the irrigation process results generally in an increase in the sodium percentage. In most of the western streams of the country, the waters tend to be gradually changed by base exchange from "hard" to "soft" waters. A determination of the magnitude of the increase which will take place as a result of irrigation uses in the Upper Basin is exceedingly difficult because of the many factors which affect such change. It may be possible to approach a reasonable answer, however, by comparison with the Rio Grande Basin where detailed records of such changes have been kept for many years. In making such comparison the dangers of applying the hydrology of one river basin to that of an adjacent basin cannot be overlooked. In this instance, however, because of the many similar characteristics of the two basins, it is believed that the figures derived by the comparison can be adopted with reasonable assurance. Quality of water records of the Rio Grande below Elephant Butte Reservoir have been obtained by the Rubidoux Laboratory since 1931, the data being published in the annual reports of the International Boundary and Water Commission. For the 22-year period up to 1952, the following averages appear. River Station Discharge-A.F. T.D.S.-T/AF % Sodium Below Caballo Reservoir 801,000 0.71 44% At El Paso 596,000 1.10 53% At Fort Quitman 209,000 2.37 62% The station below Caballo Reservoir is at the head of the Elephant Butte Project, the El Paso station is at the head of the El Paso County division of the project and Fort Quitman is at the lower end of the El Paso Valley. Considering 801,000 acre feet as the available project water supply, the net depletion at El Paso is 33 % and at Fort Quitman is 74% . Plotting the sodium percentages at the stations against the depletions (Figure 1) gives an approximate measure of the change in sodium percentage as the water supply is depleted. For the purpose of determining the worst possible effect of depletions in the Upper Basin on the quality of water delivered to the Lower Basin, it will be assumed that the virgin flow of the river at Lees Ferry does not exceed 15,000,000 acre feet per year. The average discharge with present depletions will then be -40- |
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Original book: [State of Arizona, complainant v. State of California, Palo Verde Irrigation District, Coachella Valley County Water District, Metropolitan Water District of Southern California, City of Los Angeles, California, City of San Diego, California, and County of San Diego, California, defendants, United States of America, State of Nevada, State of New Mexico, State of Utah, interveners] : |