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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28

DEPLETION OF. SURFAC.E WATER SUPPLIES

DIVERSIONS FROM GUNNISON RIVER BASIN

No significant diversions have yet been made from Gunnison River
Basin for the benefit of lands east of the Continental Divide, but
various plans have been advanced for large transmountairr diversions.
The United States Bureau of Reclamation is now considering means
for the diversion of most of the surplus water in Gunnison River
above Black Canyon. One such plan would involve a re~ervoir with
a capacity of 940,,0,0,0, acre-feet at the Curecanti site and l1 tunnel 60,
miles long from this reservoir to a point on Arkansas River near Salida
for the diversion of 50,0,,0,0,0, acre-feet per year. .
The critical period that determines ~he safe yield of GunJ;lison River
was from 1930, to 1949. A reserVOIr of about 2 million acre-feet
capacity ,:,,"ould be required to carryover a similar period Of 19 years,
and the YIeld for all purposes would be about 1 10,0, 0,0,0, acre-feet after
allowances for reservoir evaporation losses. If 'the gross demand were
reduced 10, percent, only a little more than 1 million acre-feet of stor-
age would be required at this site. This would seem to be the prac-
tical limit of the quantity of water which could be relied upon to
satisfy irrigation uses and transmountain diversions. Such irrigation
uses of this water in the Uncompahgre Valley already amount to
about 40,0,,0,0,0, acre-feet per year. Another 100,,0,0,0, acre-feet may be
needed to provide for increased consumption in the basin a90ve Cure-
canti and for extension of Uncompahgre project. Henc'e, 50,0,,0,0,0,
acre-feet per year is about the physical limit on diversions from Gunni-
son River Basin into the Arkansas River.
Preliminary estimates indicate that the total cost of a project for
the diversion of 50,0,,0,0,0, acre-feet annually would be close to $80,0,
million, of which more than $50,0, million would be chargeable to
irrigation. It is assumed t~at ~aa,aaa acre.s C?f land in the Arkansas
Valley would be served whICh IS not now IrrIgated, and that about
20,0,,0,0,0, acres more would benefit by use of return waters. :The gross
cost would thus be about $2,50,0, per acre if charged against only the
hew land and $1,250, per acre if spread over all the land to be benefited.
In its preliminary estimates of revenues, the Bureau of R~clarnation
assumed that $278 million would be received from the sale of water
to irrigators during a period of 94 years; this would be at the rate of
about $6 per acre-foot. Such payments would amortize less than
$70, million of the cost allocated to irrigation, leaving a subsidy of
more than $2,0,0,0, per acre if charged against the 20,0,,0,0,0, aeres' of
new land, and still more than $1,0,0,0, per acre if spread over all the
land which might be benefited.

RELATION OF SUBSIDIES TO DEPLETIONS

Further depletion of the flow of Colorado River by tran~mountain
diversions will thus be dependent upon the extent to which new
projects may be subsidized. It is evident that municipalities could
not independently finance all costs of construction of works for the
diversion of more than 20,0,,0,0,0, acre-feet per year. Subsidies to
irrigation under the cheapest project contemplated, involving the
diversion of 72,0,0,0, acre-feet per year, would be about $480, per acre.
Next in order is the Blue-South Platte project for the diversion of
430,,0,0,0, acre-feet per year, but the required subsidies to :irrigation

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