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",- j ,~ -. :.... ..... \',., ;, upon a study for the Colorado Water Conservation Board by the Colo- rado Water Investigation Commission. That report is dated July 1959. Work of the Enqineerinq Groups The studies by both the Upper and Lower Basin engineering groups were prepared on a strictly objective basis, with the purpose of preparing reservoir operation studies in sufficient numbers to permit appraisal of the effect of a wide variety of possible filling conditions. It was not anticipated, at least by the Bureau engineers, that it would be possible to hit on a proposed filling crteria which could be adopted "as is". , " For the purposes of this memorandum, it is not believed necessary to brief the results of those many studies. The studies have, nevertheless, been extremely helpful in arriving at the proposed filling criteria which are discussed hereafter. One general obser- vation is that all of the studies show that even a slight change in filling assumptions can create large differences in answers. This dictates that the studies can only be indicative and no one set of detailed regulations can be written in advance to cover all conditions. There must be latitude, therefore, for the Secretary to operate to a great extent on a year-by-year basis. During the course of the studies and as a result of dis- cussions within the Bureau group and with the Upper and Lower Basin groups certain conclusions became apparent to the Bureau. Neither the Upper nor Lower Basin groups can be expected to agree in all respects with these conclusions. Stated generally, these are as follows: ::;,~ :Jj: :.:;; ,", ,< (1) Nothing should be done at Glen Canyon which would have an adverse effect on the users of water for consumptive purposes below Hoover Dam or use of water from the main stem between Lake Mead and Glen Canyon. The magnitude of these uses will vary from year to year and cannot be accurately forecast on an annual basis. (2) Secondary energy should not be generated at Hoover Dam except in those times when all reservoirs are full and a spill would otherwise occur. (3) The obtaining of the minimum power head at Glen Canyon reservoir, elevation 3,490 (approximately 6-1/2 million acre-feet) at the earliest practicable time should be an objective of any filling criteria. Bureau Proposal :':"(:,; '-":.' " Basic to a solution of the filling problem is an answer to what to do about any deficiency that might occur in the firm energy generation at Hoover Powerplant incident to filling the Storage Proj- ect reservoirs. 3