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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For water year 1998 operations, Blue Mesa Reservoir will be drawn down to at least an
elevation of2283 meters (7490 feet) by December 31, 1997, in order to minimize 'icing problems
in the Gunnison River. Blue Mesa will continue to be drawn down through April 1998 to a level
that will accommodate the current most probable inflow scenario and accomplish the release
objectives with minimal power plant bypasses at Crystal.

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The minimum release objective of the Aspinall Unit is to meet the delivery requirements of the
Uncompahgre Valley Project and to keep a minimum of8,5 cms (300 cfs) flowing through the
Black Canyon of the Gunnison National Monument and to maintain a minimum of8,5 cms (300
cfs) below the diversion structure at Redlands (at the confluence of the Gunnison and Colorado
Rivers) during the summer months, Under all three inflow scenarios, Blue Mesa is expected to
fill in the summer of 1998 and flows through the Black Canyon of the Gunnison National
Monument are expected to be above the minimum release objective during the summer months,
Filling of the reservoir in water year 1998 will ensure that reasonable specific releases required
to study the protection and improvement of habitat for endangered fish can be accommodated,
The forecasted runoff for the spring of 1998 will be closely monitored to achieve these
objectives, To protect both the blue ribbon trout fishery in the Black Canyon and recreation
potential, releases during 1998 will be planned to minimize large fluctuations in the daily and
monthly flows in the Gunnison River below the Uncompahgre Tunnel Diversion,

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Navajo Reservoir

The April through July unregulated inflow into Navajo Reservoir in water year 1997 was
1,026 MCM (0,832 MAP) or 123 percent of average, Water year 1997 unregulated inflow was
1,530 MCM (1.240 MAF)or 123 percent of average, Navajo Reservoir did not fill in1997,

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Section 7 consultation with the Fish and Wildlife Service on the operation of Navajo Dam
continued in 1997, Water year 1997 was the seventh year of a seven'year study to evaluate
alternative operations of Navajo Reservoir to benefit endangered fish, In an attempt to monitor
the aquatic impact oflow winter flows on the San Juan River, winter releases were restricted to
250 cfs during the November - February period, During the spring large releases of up to 140
cms (5,000 cfs) were made during June and July to coincide with the peak flows of the Animas
River, This resulted in peak flows of305 cms (10,800 cfs) at Bluff, Utah, After the completion
of the large spring releases, releases were gradually reduced to approximately 17 cms (600 cfs)
for the remainder of the year,

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In water year 1998, Navajo Reservoir is expected to nearly fill only under the probable
maximum inflow scenario, The reservoir should fill above 80 percent of full under the most
probable and probable minimum scenarios, Releases from the reservoir will be held near 17 cms
(600 cfs) through the fall and winter months and large releases will likely be made in May and
June in order to improve the habitat and provide better spawning conditions for endangered fish
in the San Juan River,

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September 3, 1997

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