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( 0;)2329 \ I 32 ASSEMBLY INTERIM COMMITTEE ON WATEIt the Department of the Interior in projecting the futur~,rate of Upper Colorado River Basin depletions reflect, almost entirely, dJfferent judg- ments as to: " 1. The scope and bmIng of construction of Federal R\clamation projects in the Upper Basin. 2. The magnitude and timing of future industrial demands for water such as represented by the oil shale industry. 3. The magnitude and timing of future municipal and domestic water demands. ' , Such differences in estimated. development raise uncertaip.tiesl{!i1 va: rious areas as to anticipated future supplies. Until the. estinyttes of the state and federal agencies are more nearly agreed we ca<llnot be certain as to when critical shortages will occur. As is described,.below, estimated Upper Basin development particularly, is a maj<;>:r factor in determining silpplies available to the Lower Basin. .' .. .. These differences between the projections of UpPcJr Basin de~~lqp- ment by the two agencies are summarized in the foll/owing tabulation: I . . Colorado River Department of Board of Calif. * Interior * , (1.000 A.F.) (1,00fl)iF~f ? 1975 __________ 4,300 4,000 1990 __________ "',400 4,900 2000 _________ _ 5,700 .5,430 . Total for re!"..jervolr losses and other depletions. Year Difference (i,OdO A:F.) : 306 500 270, Thp",lJepartment of the Interior's projection, in general, envisages an ;illcrease over historic trends in the ratc. of Upper Basin depletions ,until the year 1975. Such an increase obviously will result from the construc- tion and operation of federal projects authorized in recent years, principally the Colorado River Storage Project and participatipg proj- ects, the Fryingpan-Arkansas Project, and the San Juan-Chama and Navajo Indian Irrigation Projects. After 1975 the department expects the 1960-1975 rate of increased depletion to reduce until the year:20dO, after which it will further tend to level off 'as the Upper Basin ap- proaches full use of its share of Colorado River Basin water. The impact of this expected development, coupled with natural flows expected in the river for use in both the upper and lower basins is dis- cussed in the sections below. . . COlORADO RIVER WATER SUPPLY The Colorado is characterized by uneven and. unpredictable flows. A vaiIable flow data indicates that the flow has varied from 4,;39~,400 acre-feet in 1934 to 22,~03,000 acre-feet in 1907. The. ;river's early l:1is~ tory was marked by "vIOlent floods causing great damage." 9 In addi- tion to erratic flow, prior to construction of Hoover.and Glen 'Cil.llyon Dams, the river carried large quantities of silt, estimated during the suit, ArizO'na v. California, as being "proportionately 17 times that of the Mississippi River." 10 . 9 Report of Special Master, op. cU." at 18. 10 Ibid." at 20.