BOARD01635

• Board Meeting Date: 3/26/1945
• Description: Table of Contents and Minutes
• Board Meetings - Doc Type: Minutes

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comparable in completeness and accuracy with that of the Bureau of Reolama-
tion. Colorado says, however, that U. S. Census Bureau data conoerning
populations are used in the Report; and' that Census Bureau reports on irri-
gation should not be disregarded inasmuch as they are ,the principal squrces
of information for the historio period during whioh depletions and virgin
flows have been oaloulated, and is information whioh has been oompiled in
eaoh oensuS' year under llniform dsfini tions that are applicable to both ba-
sins and all States alike.

32. The quantity of water oonsumed within the natural basin above
Lee Ferry, by the irrigation of 1,256,800 aores of land therein, is esti-
mated in the Report at 1,948,000 aore feet annually. Although unit rates
of water consumption are not disclosed in the Report, the total is equiva-
lent to 1.55 acre feet per aore irrigated, and the Report assumes the same
oonsumption per year in both drouth oyoles, such as 19~1-194P and in normal
or long-time periods. Colorado engineers estimate that total water oon-
sumption within the Upper Basin by existing irrigated lands will average
2,Ol~,Ooo acre feet under normal oonditions, - a figure derived from the
application of a somewhat smaller unit rate to a somewhat greater aoreage, -
and will average 1,812,000 acre feet per year during a drouth oyole suoh
as 1931-1940. Colorado engineers say that the unit rate of water consump-
tion adopted in the Report may be applicable to the problem of estimating
water consumption in the basin under full-supply conditions, but that the
adopted vate may be too high, considering the relatively large aoreage
served by unregulated and erratio tributary streamflows, for whioh present
irrigation is inadequate. They say that water oonsumption in the average
year of a drouth cycle such as 1931-1940 is necessarily sub-normal for the
reason that diversions and applications of water, the oontributions to
ground storage, and the return flows dur1ng'suoh a period are below average;
that muoh of the acreage is irrigated indifferently ~d some not at all
during drouth cycles; that transpiration losses are reduoed by the impair-
ed crop yields; and that the above mentioned factors more than offset the
higher temperatures and evaporation rates of lon@Sr drouth seasons. Colo-
rado says the Report reoognizes the sub-normal depletions of drouth oyoles
with'respeot to both expert diversions and evaporation losses from main-_
stem reservoirs, and suggests the same reoognition be given to water oon-
sumption incident to the irrigation of lands wi thin the natural basin.

~3. Existing export diversions above Lee Ferry, for use outside ,the
natural basin, exolusive of allowanoes for future exportations of author-
ized projeots, are estimated in the Repor~ at 102,000 aore feet in Colo-
rado and 66,000 acre feet in Utah, or a total of 168,000 aore feet per
year during a drouth cyole such as 19~1-194D. Details are not shown for
normal oonditions, and the stmIlJ1ary tabulation (pages 10~ and 104) is oon-
fusing beoause unspeoified amounts of water diverted from one division
to an6ther~ or one State to another, within the natural basin, are in-
cluded in the totals reported for export diversions. Colorado suggests
that suoh diversions within the natural basin be exoluded from the Re-
port, or if inoluded be designated "trans-division," or "trans-state" di-
versions, and be segregated and summarized, separately from "export diver-
sions," whioh term is applicable to and should be reserved for the waters
diverted from the Colorado River system for use outside the natural basin.