9603

• UCREFRP Catalog Number: 9603
• Author: Clayton, R. and A. Gilmore.
• Title: Flaming Gorge Environmental Impact Statement Hydrologic Modeling Study Report - Results of Action and No Action Alternative Analysis.
• USFW Year: 2001.
• USFW - Doc Type: \
• Copyright Material: NO

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4
I. Achieve peak of 26,400 cfs for at least I day in 10% of all years.
2. Sustain peak of 22,700 cfs for at least 2 weeks in 10% of all years.
3. Sustain peak of 18,600 cfs for at least 4 weeks in 10% of all years.
4. Achieve peak of 20,300 cfs for at least I day in 30% of all years.
5. Sustain peak of 18,600 cfs for at least 2 weeks in 40% of all years.
6. Achieve peak of 18,600 cfs for at least I day in 50% of all years.
7. Sustain peak of 8,300 cfs for at least I week in 90% of all years.
8. Sustain peak of 8,300 cfs for at least 2 days in 98% of all years.
9. Achieve peak of 8,300 cfs for at least I day in 100% of all years.

These requirements were derived from Table 5.5 in the 2000 Flow Recommendations.
The 2000 Flow Recommendations are divided into five separate categories depending on the type
of hydrologic conditions experienced in the Upper Green River Basin. The objectives described
above aggregate all of the flow objectives in the separate categories of the Flow
Recommendations into one group.

The Action Alternative also has flow objectives for the summer, autumn and winter.
During this period (August through February), the Action ruleset controls the releases from
Flaming Gorge Dam to achieve flow objectives for Reach One and Two while attempting to
lower the reservoir water surface elevation to a target of 6027 feet above sea level by the
beginning of March. The Action ruleset maintains releases to .achieve the flow objectives during
the base flow period unless the reservoir elevation rises to 6040 feet above sea level or greater.
When this occurs, releases are controlled by a maximum storage rule that prevents uncontrolled
spills. When the inflow into Flaming Gorge during the base flow period is greater than
anticipated, and the elevation is below 6040, the flow objectives are maintained and the target
elevation will not be achieved. Releases during March and April attempt to reset the elevation of
the reservoir to 6027 feet above sea level by the beginning of May by making releases in the
range from 800 to 4600 cfs.

The No Action Alternative has spring flow objectives that are less specific than the
Action Alternative. Instead, the flow objectives of the No Action Alternative focus more on
flows during the summer and autumn period. The flow objectives of the No Action Alternative
during the spring require a peak release with a magnitude of at least 4600 cfs (power plant
capacity) and a duration from I to 6 weeks in all years. In wet years, the No Action ruleset
makes the duration of the peak release approach 6 weeks in length. In dry years, the duration is
set to at least 1 week in length. The No Action ruleset determines a spring release volume by
attempting to control the reservoir elevation to achieve a fill target for the end of July. This
volume is then shaped into a spring peak hydrograph that achieves the spring objectives
described above.

During the summer and autumn (before October), releases from Flaming Gorge Dam are
managed by the No Action rule set so that flows in Reach Two are between 1100 and 1800 cfs.
In October releases are managed so that flows in Reach Two are between 1100 and 2400 cfs.
From November through February, there are no restrictions placed on flows during the base flow