WSP11823

• File Number: 8281.400
• Description: Colorado River Studies and Investigations -- Colorado River Depletion Projections
• Basin: Colorado Mainstem
• Water Division: 5
• Date: 3/25/1955
• Title: Report on Depletion of Surface Water Supplied of Colorado West of Continental Divide
• Water Supply Pro - Doc Type: Report/Study

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DEPLETION OF SURFACE WATER SUPPLIES

able 'in 1917 for storage of all floods since then. Such a reservoir, or
combination of reservoirs, would not have filled until] 930, as shown
on plate A, and would not have been more than half full at any time
during the past 19 years. Furthermore, even if the next 13 years
should be as wet as those from ]917 to 1930, these storage reservoirs
would not refill until 1965, a carryover of 35 years. If such a series
of wet years should not recur, the delivery of 75 million acre-feet at
Lee Ferry in each 10 consecutive years could not be maintained with
. depletions of 7.5 million acre-feet per year in the upper basin. .
. . While it is true theoretically that there could have been annual
depletions in the Upper Basin aggregating 7.5 million acre-feet without
breach of the provisions of section (d) of Article III to the present time,
. it is believed that a more conservative value should be used in the
. planning of new projects until the supply actually available to the
: upper basin has been determined by many more years of record.
. Should the years of carryover of water in storage be limited to the
period from 1930 to 1952, the aggregate depletion of the natural
supply in the Upper Basin could not be more than 6.2 million acre-feet
. per year. A total of about 21 million acre-feet of reservoir capacity
would be required for regulation under this condition with the delivery
of 7.5 million acre-feet annually at Lee Ferry to comply with the
provisions of section (d)bf Article III of the Compact. The perform-
Jance of such reservoirs is shown on plate B. Initial filling would have
,had to commence in 1927, the reservoirs would have been full in
1930, substantially empty just prior to the flood in the spring of 1941
,and would have refilled only in ]952. .

Upper Colorado River Basin Compact
The Compact of 1922 did not apportion water among the several
States. This was done as to the upper basin in the compact entered
into in 1948 without change of any of the provisions of the earlier
compact. Basically, there was apportioned to Colorado 51.75 percent
of the total quantity of consumptive use per annum apportioned in
perpetuity to, and. available for use each year by, the upper basin
:under the Colorado River Compact, after allowance of 50,000 acre-feet
per annum apportioned to Arizona.
J This percentage of the difference between 50,000 acre-feet and
7,500,000 acre-feet amounts t03,855,375 acre-feet per year. The same
percentage of the difference between 50,000 acre-feet and 6,200,000
acre-feet would be 3,182;625 acre-feet per year.
. It is the position of Colorado and of the other States signatory to
the 1948 compact that credit should be taken for any reductions in
:iJ.atural depletions which may be brought about by construction of
.!lew works but that they will be responsible for evaporation losses
from reservoirs including those required to provide for the delivery of
15 million acre-feet of water at Lee Ferry during each period of 10
Ilonsecutive years.
It is our understanding that Colorado anticipates that its share of
the maximum allowable depletion caused by acts of man will be
4,043,000 acre-feet per year and that the evaporation losses charge-
able to Colorado would be 3]6,000 acre-feet per year. This would
ltlave 3,727,000 acre-feet as the limit (under section (a) of article III
of the Colorado River Compact) of all depletions in Oolorado arising
from consumptive uses by agriculture, consumptive uses by industry,
IJ!Ild diversions out of the drainage basin of Colorado River.

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