WSP02781

• File Number: 8220.101.12
• Description: Glen Canyon Dam/Lake Powell
• State: AZ
• Basin: Colorado Mainstem
• Date: 10/14/1997
• Title: Annual Operating Plan for Colorado River Reservoirs - 1998
• Water Supply Pro - Doc Type: Annual Report

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1998 DETERMINA nONS

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The AOP provides guidance regarding reservoir storage and release conditions during the
upcoming year, based upon Congressionally mandated storage, release, and delivery criteria and
determinations, After meeting these requirements, specific reservoir releases may be modified
within these requirements as forecast inflows change in response to climatic variability and to
provide additional benefits coincident to the projects' multiple purposes,

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Upper Basin Reservoirs

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The Operating Criteria provide that the annual plan of operation shall include a determination
of the quantity of water considered necessary to be in Upper Basin storage at the end of the
water year, Taking into consideration all relevant factors required by the Operating Criteria, it
has been determined that the active storage in Upper Basin reservoirs forecast for September 30,
1998 exceeds the storage required under Section 602(a) of the Colorado River Basin Project Act
under any reasonable range of assumptions which might be applied, Therefore, "602(a) Storage"
is not the criterion controlling the release of water from Glen Canyon Dam during water year
1998,

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Section 602(a)(3) of the Colorado River Basin Project Act provides for the storage of Colorado
River water in Upper Basin reservoirs that the Secretary of the Interior finds necessary to assure
deliveries to comply with Articles ID( c) and ID( d) of the 1922 Colorado River Compact, without
impairment to the annual consumptive use in the Upper Basin, The Secretary is required to
make this determination after consultation with the Upper Colorado River Commission and
representatives from the three Lower Division States, and after taking into consideration all
relevant factors including, historic stream flows, the most critical period of record, the
probabilities of water supply, and estimated future depletions, Water not required to be so stored
will be released from Lake Powell:

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to the extent it can be reasonably applied in the States of the Lower Division to the uses
specified in Article III(e) of the 1922 Colorado River Compact, but these releases will
not be made when the active storage in Lake Powell is less than the active storage in
Lake Mead,

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to maintain, as nearly as practicable, active storage in Lake Mead equal to the active
storage in Lake Powell, and

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to avoid anticipated spills from Lake Powell,

Spill avoidance and/or storage equalization criterion in accordance with Article II(3) of the
Operating Criteria will control the releases from Glen Canyon Dam during water year 1998
unless the minimum objective release criterion in Article II(2) is controlling, Under the most
probable inflow scenario Glen Canyon Dam will release 13,260 MCM (10,750 MAF),

September 3, 1997

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