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Show limited in amount and (2) that it is a temporary condition. Because the individual Upper Basin projects all consume relatively small amounts of water compared to the total amount of water in the main rivers, the effect of such flushing by one or even several new projects constructed concurrently will have little net effect upon the quality of the water supply at Lees Ferry. Further, most of such leaching will have been completed long before the ultimate project is developed. In this report, therefore, no attempt has been made to evaluate the temporary effect of soil leaching on water quality in considering either the initial phases or the ultimate development of the project. In 1948-49 a comprehensive study of Lake Mead* was conducted by the Department of the Navy in cooperation with the Department of Interior, Department of Commerce, University of California and others. The report, now in the process of publication, covers a detailed study and analysis of most of the physical phenomena and changes which occur in the operation of this large holdover reservoir. One of the principal effects of storage is the mixing of the varying qualities of the seasonal runoffs of the stream. The relatively saline flows of the fall and winter months are sweetened by the better quality spring runoffs from snowmelt. Summer torrential flows may be either better or worse than the average qualities depending upon the areas drained by such storms. Further discussion of the smoothing effect of holdover storage on quality of released water will be found later in the report. Since no salts are removed from solution by the evaporation process, the increase in salinity concentration resulting from reservoir evaporation will vary directly with the amount of such evaporation. The Lake Mead studies indicate two other phenomena which have an effect upon the quality of water passing through the reservoir. Analysis of the qualities of inflow and outflow together with studies of the reservoir water itself show that some salts are actually precipitated out of solution in the storage basin. These salts, which in general comprise the less soluble constituents, seem in part to be precipitated because of temperature changes and in part to be carried down by the gradual settling of the finely divided sediments transported by the inflowing streams. In Lake Mead, the Virgin River branch or Overton Arm of the reservoir basin contains substantial deposits of sodium chloride and gypsum. The effect of these soluble beds on the quality of Lake Mead waters gave some concern to the geologists and others who studied the matter prior to Hoover Dam construction. Although studies indicate that some solution from these beds has occurred during the past 19 years of operation, the amount of such solution has not been as great as was originally feared and seems to be decreasing yearly as the beds become covered by silt deposits. C. S. Howard * "Lake Mead Comprehensive Survey of 1948-49, by W. O. Smith, C. P. Vetter, G. B. Cummings and others, February 1954" in three volumes. -27- |
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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] : |