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, . .... -.., the river with a close water supply, it is expected that the lI/IIOunt could be reduced somewhat. Nevertheless, for purposes of this study, 1,762,000 acre-feet should be a part of the assumed releases. The item of "unaccounted-for-water" consists of the average amount necessary to be placed algebraically in the hydrologic equation in order to balance that equation under the conditions encountered during the operating years 1951-1956. It includeereaervoir losses, crnL~el losses, ~npoun~~ent and recovery of bank storage, inflow from tributary streams, unmeasured diversions, unmeasured returns, and errors in stream flow measurementso Tbe amount is 508,000 acre-feet, which ie the average of the annual amo~~tB shown in Table IV. It is estimsted that by the year 1970 demanda will be made upon Lake Mead to meet downstream uses in the United States and Mexico to ths extent of about 8,900,000 acre-feet; the derivation of this estiJate is sho'oln on Table V. By use of this figure, it is not intended to implY' that this figure represents the legal bounds ot permissible use under the ,- law of the r1 ver. Operation of Lake Mead for Power J.3 -,,3 () Firm power from the Boulde~nyon project is defined under the Hoover Dam power contracts aa~miilion kilowatthours annually with III diminution of 8.76 million kllowatthours lIU1ually after operating year ending May 31, 1938. In ytlars of high runoff, when excess flow would be available and the reservoir nearly full, such excess flow may be used for the generation of secondary energy. During the immediate past few 19ars, due to severe drought and low reservoir content, some shortages have occurred in the firm energy generation. It is estimated that by April 1, 1958, the active content of Lake Mead will be about 20,000,000 acre-feet. Table VI summarizes the operations of Lake Mead and Glen Canyon Reservoirs, under the premises adopted for these stUdies, during the years 1958-1970, inclusive. SUI1Il'llB.ry of Assumed Operation In the years 1958 to 1961, inclu8ive, the entire flow of the Colorado River would have been bypassed at Glen Canyon Dam site. In these years Lake Mead storage would have been drawn down to an active . content of 20,000,000 acre-teet at the .pd of each operating year. In these years a total of about 13,300,000 ac!'8-feet would be available for generation of secondary energy at Hoover. In the year 1962, storage would have been initiated at Glen Canyon Id.th about 1,000,000 acre-teet being impounded. In that year, due to the availability of vacant storage 8pece in the Glen Canyon Reservoir, in lieu of producing secondary energy at Hoover poverplant about 1,800,000