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

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September 30, 1950, averaged about 700,000 acre-feet per year,
equiv,alent to 168 acre-feet per square mile.
Thll extreme southerly portion of Colorado lying west of the Con-
tinental Divide is drained by San Juan River and its tributaries, most
of wliich loin San Juan River in New Mexico. The combined drain-
age ll!'rea In Oolorado amounts to 5,889 square miles. The average
annual flow across the boundary of Colorado during the 10-year
period ending September 30, 1950, was about 1,880,000 acre-feet,
equivMent to 319 acre-feet per square mile.
Most of such variations in runoff per square mile of drainage area
are due to differences in the elevation of the watersheds. Precipita-
tion on the high mountains is much greater than in areas of lower
elevation and consumptive uses at high altitudes are less, due to pre-
vailing low temperatures and shorter growing seasons. Hence, a
large j:)art of the total contribution of each stream originates near its
headwltters. For example, the average runoff per square mile from
drainage areas above 9,000 feet in elevation, for the same 10-year
period,' was found to be 1,000 acre-feet per year on the RoarinK Fork,
600 acte-feet per year in the Colorado River Basin east of Gore Range,
and 440 acre-feet per year in the upper portion of Gunnison River
Basin.

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LIMITATIONS ON USE

Colorado has entered into two interstate compacts limiting its use
of Oolor;ado River water: the Colorado River Oompact signed in 1922;
the UpI1er Colorado RiverBasin Compact signed in 1948. The former
allocate!l the waters of the stream system between the upper basin and
the Lower Basin; the latter allocated the Upper Basin share among the
States in that basin.

OoloradO, River Oompact
During the 30 years which have elapsed since the Colorado River
Oompac~ became effective, many disputes have arisen regarding the
intent and applicability of various provisions. However, for purposes
of this report we need be concerned only with two sections of Article
III in w~ich the waters of the Colorado River system are allocated;
(a) Thete is hereby apportioned from the Colorado River system in perpetuity
to the UPRer Basin and to the Lower Basin, respectively, the exclusive beneficial
consumptIve use of 7,500,000 acre-feet of water per annum, which shall include
all water n~cessary for the supply of any rights which may now exist.
* * * * * * *
(d) The :States of the upper division will not cause the flow of the river at
Lee Ferry to be depleted below an aggregate of 75 million acre-feet for any period
of 10 conse'cutive years reckoned in continuing progressive series beginning with
the first da! of October next succeeding the ratification of this compact.
When this compact was negotiated it was thought that the flow
of Colorado River under natural conditions would average considerably
more than 15 million acre-feet per year. It is now evident that such
is not thei case and that the provisions of section (d) of Article III
will probaibly limit depletions of the waters of the upper basin to
some amount less than that allocated in section (a) of the same article.
In order for the requirement of section Cd) of Article III to have
been satisfied during the past 36 years, with depletions in the upper
basin aggregating 7.5 million acre-feet per lear, it would have been
necessary to have had 38 million acre-feet 0 reservoir capacity avail-

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