WSP07506

• File Number: 822.600.10
• Description: Colorado River Annual Operating Plan - Annual Reports
• Basin: Colorado Mainstem
• Date: 1/1/1998
• Author: USDOI/BOR
• Title: Annual Operating Plan
• Water Supply Pro - Doc Type: Annual Report

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Lake Powell

The April through July unregulated inflow into Lake Powell in water year ]997 was ]3,964
MCM (11.321 MAF) or 147 percent of average. Water year 1997 unregulated inflow was
20,057 MCM (16.261 MAF) or 139 percent of average. Lake Powell ended the water year
8 feet from full.

During March and April 1996, a test of the Beach/Habitat Building Flow was conducted from
G]en Canyon Dam. The test consisted of peak releases of 45,000 cfs which lasted 7 days,
preceded and followed by 4-day periods oflow steady flows to allow photographic mapping and
monitoring of the canyon resources. Scientific understanding and results of this test were
presented in a symposium held Apri] 8 - 10, ] 997.

This test was implemented following discussions between the Department of the Interior, the
Basin States, and key scientists and researchers which resulted in a long term agreement for
managing spills from G]en Canyon Dam. This agreement provides for the use of reservoir
releases in excess of power plant capacity required for dam safety purposes during high reservoir
conditions to accomplish the objectives of the Beach/Habitat Building Flow described in the
Record of Decision for the Glen Canyon Dam Final EIS (GCDFEIS). Such releases would be
consistent with the] 956 Colorado River Storage Project Act, the] 968 Colorado River Basin
Project Act and the ]992 Grand Canyon Protection Act. Such releases would be managed to the
maximum extent possible to (1) protect river sediment storage downstream or (2) be released
in such a way as to reshape river topography, redeposit sediment and enhance aquatic habitat.
With current full reservoir system conditions, there is a possibility releases above powerplant
capacity will be necessary in 1998. Such releases would be made consistent with the ] 956
Colorado River Storage Project Act, the 1968 Colorado River Basin Project Act, and the] 992
Grand Canyon Protection Act. In accordance with the GCDFEIS and the Record of Decision,
Reclamation intends to reinstall the spillway gate extensions at Glen Canyon Dam to increase
the flexibility of managing high runoff years.

During water year 1998, releases greater than the minimum release objective of ] 0,] 52 MCM
(8.230 MAF) likely will be made to avoid anticipated spills and/or to equalize the storage
between Lakes Powell and Mead. Under the most probable inflow conditions, releases of ] 3 ,260
MCM (10.750 MAF) would be made, while under the probable maximum inflow scenario,
approximately 21,759 MCM (17.640 MAP) will be released. This maximum probable inflow
would require releases of about 708 cms (25,000 cfs) for a lengthy period of time.

The interim flow restrictions on the daily and hourly releases from Glen Canyon Dam
implemented in August, 1991 were replaced during water year 1997 by the parameters of the
Record of Decision for the GCDFEIS preferred alternative. Operating criteria and a plan of
operations were issued on February 24, ] 997, in accordance with the 1992 Grand Canyon
Protection Act. A monitoring and research program has been implemented and will continue
to measure the effect of operating criteria on downstream resources as part of the Adaptive
Management Program. Releases from Lake Powell in water year 1998 will continue to reflect

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