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~ i"'.i~ ., ;:,\ ;; J Appendix "A" (Cont'd) Revised December 1957 -Las Vegas, Nev. (b) California (c) Nevada (d) Mexico (e) Unaccounted for water 5, 362, 000 acre-feet 46,000" " 1,762,000" " 508,000" " (4) Power is to be generated at Hoover to the extent that water re- quired to meet downstream uses, as defined in (3) above, will permit such generation. If such releases do not permit generation of firm power as defined by contract, then Lake Mead storage would be drawn upon for firm power, except that when Lake Mead storage is thereby drawn down to 17,000,000 acre-feet (active), the accumulation of addi- tional storage in Glen Canyon Reservoir shall be restricted to the ex- tent necessary to permit continuance of firm power production at Hoover without further demand upon Lake Mead storage, Water already stored in Glen Canyon Reservoir shall not be released, however, for continu- ance of firm generation at Hoover. .... Reservoir operations will necessarily depend upon the conditions of use, of flow, and of storage as they develop. If in the course of actual operations during the period 1958-1970 there are appreciable deviations from average flows the foregoing premises, including the criteria for operation of Glen Canyon and Hoover, should be reconsidered. Application and further discussion of, and the resulting computations under the foregoing basic premises are contained hereinafter. Assumed Stream Flow Conditions An assumption as to expected stream flows is necessary in any reservoir fill- ing demonstration. The assumption of average stream flow conditions is a reason- able one for this study. Reservoir operation studies presented herein assume aver- age stream flow at Glen Canyon equal to that obtained from the period 1914-1945 in- clusive, modified to reflect present conditions of development and progressively re- duced each year through the operation period consistent with a projected schedule of increasing annual depletions. Of course, stream flow realized at Glen Canyon will depart from the average in any given year, but speculation involving variants in the developing physical situation is premature and would not be useful. Lake Mead storage reached a low point immediately prior to the 1957 flood season due to a recent drought (1953-56 being the lowest four years in sequence in the history of the Colorado River). The flood run-offin 1957 was considerably greater than average and Lake Mead active storage content is expected to be 20.0 million acre-feet on April 1,1958. Therefore Refers to clarifications by Interior to "Hydrologic Bases" discussed in Washington October 24, 1957. 1/ . I MA&">INt>- A;"T'E: -ii- THIS 72.",-vIS/CN /5 INC"....tt..'=--rrr: - A t'o."'1fl-w--,e fA"'1i!. V.~R. SIOIV ,5. A rrA c/fsJ) r" f"'b<=S)