FOREIGN RELATIONS, 1942, VOLUME VI



lower basin of the United States at the present time will use 9,140,000
acre-feet of Colorado River water per year. This is 640,000 acre-feet
more than the firm allocations of the Colorado River Compact to the
lower Basin States. These projects do not comprehend the total
possibilities of the lower basin.
  In addition it must be borne in mind that we are here dealing
with average figures which do not take into account extended peri-
ods of low run-off such as have been recently experienced, where
American developments would necessarily be deprived of sufficient
water if any substantial amount was guaranteed to Mexico. It is
quite possible that in years of abnormal run-off 2,000,000 acre-feet
of water or more could be delivered to Mexico without deprivation
to lands in the United States, even after ultimate developments in
the United States. In the average year, however, the amount that
could be so delivered would be very much less than this figure, and
during dry cycles much less than 1,000,000 acre-feet would be avail-
able without serious deprivation to American interests.
  Mexico's estimates of the water supply and that amount which will
be available for ultimate use were undoubtedly based on early figures
which have been shown by later surveys to be inaccurate. When
the Colorado River Compact was negotiated in 1922 it was assumed
that total water production in the basin was about 19,000,000 acre-feet.
Sixteen million acre-feet were allocated by the Compact. Subse-
quent stream flow records have indicated that the 1922 estimate was
too high. In this connection it is of interest to note that as gauging
facilities have been improved, the estimates of virgin flow of the
river have tended to decline, so much so as to place in some doubt
the present estimate of 18,000,000 acre-feet. The total water produc-
tion of the basin, including the Gila River, during the low run-off
period, 1930-1940, averaged only about 14,500,000 acre-feet per year,
or 1,500,000 acre-feet per year short of the Compact allocations. If
such a 10-year cycle occurred at the end of the 50-year amortization
period provided for Boulder Dam and appurtenant facilities, it is
estimated that the release from Lake Mead would be only about
8,500,000 acre-feet per year and this would be made possible only
by drawing the contents of the reservoir down 17,000,000 acre-feet
during the 10 year period.
  Furthermore, no account has apparently been taken in the data
cited in the Ambassador's memorandum of March 19, of reservoir
evaporation losses, which are estimated as being in excess of 1,000,000
acre-feet annually, thus materially reducing the amount of water
available for distribution, either to the United States or to Mexico.
  Existing projects below the dam will require 7,800,000 acre-feet
of this annual release of 8,500,000 acre-feet without taking into con-



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