WSP01866

• File Number: 8220.105.LJ
• Description: Navajo Reservoir
• State: NM
• Basin: San Juan/Dolores
• Date: 10/1/1984
• Title: Draft Hydrologic Determination - October 1984 - Water Availibility from Navajo Reservoir and the Upper Colorado River Basin for Use in New Mexico
• Water Supply Pro - Doc Type: Report/Study

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III. aydrolog1~ Investigation

!he Depart..nt of Interior's present po.ition on water availability in the Upper
Basin is that for planning purposes, it will be assumed that up to 5.8 MAl of
water can be 'afely depleted annually in the Upper Sasin. !his Qumber was
derived froa three a.sumptions: (1) the lowest 3~-year period of natural
runoff; (2) tolerable shortages to irrigated agriculture; and (3) delivery of
half the Mexican Treaty ~omm1tment from the Upper Basin.

As to water use in the Upper Ba.in, sub. action (b) of Article III of the Upper
Colorado River Basin Compact permits New Mexico or any other Upper Ba.in State
to use waters in exce.. of it. percentage allotment, provided such excess use
doe. not prohibit any of the reMaining State. from ut~lizing its re.pective
allotment. Thu., the availability of Navajo Reservoir watar for .unicipal and
indu.trial purpo.e. in New Mexico beyond the year 2005 depend. upon the extent
of water use in .the entire Upper Basin beyond year 2005 a. well a. upon the
phy.ical availability of water in Navajo a..ervoir.

To avoid a critical compact interpretation, we a.sume that the Opper Ba.in will
be obligated to deliver 75 MAl of water every 10 years at Lee Ferry, plus
750,000 acre-feet annually toward Mexican Treaty deliverie.. This would require
an average annual water delivery ~t Lee Ferry of 8.25 ~~. Thi. a..umption i.
not to be eonaidered a. an interpretation of the Upper Basin obligatioG for
water delivery at Lee Ferry under the Colorado River Coapact. It repre.ent.,
rather, a practical and conservative approach for the purpo.e. of the pre.ent
determination required by sectioG 11(a) of Public Law 87-483.

!hroughout the hydrologi~ investigation, and as ~emonstrated in the'attached
tables, present Colorado River Storage Project (CaSP) operating policy, alona
with required Upper Sasin water deliverie., eombine ~o form the underlying
aseumption. that are integral to a hydrologic determiLation of water. avail-
ab~lity from Navajo Reservoir and the Upper Colorado River Ba.in for use in
New Mexico.

An estimate of projected water depletions for Bureau of Reclamation projects,
together with non-Federal projects, inditates that total depletions in the Upper
Basin will Qot reach 5.8 MAl until some time after year 2030 and very likely not
until year 2040. !he table of "Projected Water Supply and Depletion., Upper
Colorado River Basin" dated September 1984, which is appended to this report,
shows the projected timing for development of the water apportioned to each of
the Upper Ba.in State. Within this 5.8 MAl limit: Arizona, 50,000 acre-feet;
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Colorado, 2,976,000 acre-feet; New Mexico, 647,000 acre-feet; Utah,
1,322,000 acre-feet; Wyoming, 805,000 acre-feet. !he Upper Basin States have
reviewed tbi. table and, although they do not ne~essarily agree, they have
eho.en noc to object. !he State of Wyoming has said that it reserves the right
to submit a formal obje~tion.

A. Study Ap~roa~h

The present operation of the reservoirs 0: the ColoradO River Sy.tem in
ac~ordance with Publi~ Law 90-537 Operating Criteria is based on a Simple for-
mula approach that indicates water available for upper Basin ~onsumpt1ve use
would be limited to an average of 5.8 HAl annually if delivery to the Lower
Basin 0: 8.25 HAl is maintained during low flow periods similar to the most