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<br />9 . DISCUSSION OF "PRESEl'lT" DEPLETIONS.
<br />
<br />In the synopsis (page 6) the Report says: "Stream depletions in the upper
<br />Basin now average more than 2,400,000 acre feet a year. In the Lower Basin the
<br />depletions are near 4,500,000 acre feet." The two figures are not directly
<br />comparable. The Upper Basin figure is based on drought cycle (1931-1940)
<br />conditions, and includes allowances for future depletions by projects under
<br />construction and authorized, whereas the Lower Basin figure is based on long-
<br />time (1897-1943) average conditions, and (in this instance) is exclusive of
<br />allowances for future depletions incident to the irrigable lands of existing
<br />enterprises that are not yet irrigated.
<br />
<br />Figures for both basins shown in the foregoing table are long-time averages.
<br />Present (actual) depletions are 2,129,000 acre feet in the Upper BaSin, and
<br />4,497,100 acre feet in the Lower Basin, exclusive in both instances of allowances
<br />for future increased depletions. Including the allowances made by the Bureau
<br />of Reclamation, to indicate conditions when authorized projects c <lne into
<br />operation and irrigable lands of existing enterprises are brought under irriga-
<br />tion, the depletions will amount to 2,620,000 acre feet annually in the Upper
<br />Basin, and 8,762,000 acre feet annually in the Lower Basin.
<br />
<br />Since the flow of the Colorado River as recorded at Lee Ferry (inc. Paria)
<br />during 1931-1940 averaged 10,167,000 acre feet per annum, it would be possible
<br />for upstream depletions to increase, over and above those which actually exist,
<br />by 2,567,000 acre feet per year, without thereby reducing the flow at Lee Ferry
<br />below 75,000,000 acre feet during a similar period of ten consecutive years,
<br />should all,)' such drought cycle again occur, and without constructing all,)' so-
<br />called replacement storage.
<br />
<br />Projects which might deplete the Lee Ferry flow by 2,567,000 acre feet per ','
<br />annum during such a drought cycle would involve depletions under nomal condi-
<br />tions of about 3,200,000 acre feet annually. With allowances for future
<br />depletions by projects now under construction and authorized of 500,000 acre
<br />feet, it would be possible to construct potential projects with aggregate
<br />nonnal depletions of 2,700,000 acre feet annually, without re'luiring the con-
<br />struction of any replacement storage reservoire, and without danger of depleting
<br />the Lee Ferry flow below 75,000,000 acre feet in ten years, even though a
<br />drought cycle such as 1931-1940 should occur after all such projects are con-
<br />structed and in operation.
<br />
<br />Inasmuch as the estimated depletions of all potential Upper Baein projects
<br />listed in the Report, exclusive of main stem power and replacement reservoirs,
<br />totals approximately 4,000,000 acre feet, more than half of the irrigation and
<br />export diversion program could be completed, before the need for replacement
<br />storage would arise, and without impairing the ability of the Upper Basin to
<br />deliver 75,000,000 acre feet of water or more during each period of ten
<br />consecutive years, even though a drought ~cle such as 1931-1940 should again
<br />occur.
<br />
<br />Extensive revisions of the Report are needed, first, to convert the Upper
<br />Basin data from drought-cycle (1931-1940) averages, to long-time (1897-1943)
<br />
<br />(14)
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