9602 ‎(2)‎

• UCREFRP Catalog Number: 9602
• Author: Clayton, R. and A. Gilmore.
• Title: Flaming Gorge Draft Environmental Impact Statement Hydrologic Modeling Report.
• USFW Year: 2002.
• USFW - Doc Type: \
• Copyright Material: NO

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5
In yews classified as dry or moderately dry, the difference between the Action and No Action
alternatives, in terms of minimum duration, can have a significant impact on the reservoir
elevation. When dry years occur in series, which is often the case, the year to year differences in
reservoir elevation caused by the operational regime can compound upon each other as shown in
this case.
T;~..,,.., ') iJ.,~~,,..~..:,. i?nlc~ncoc rTn~lor tha Mnct Tntnncn ThrPP VPAr l~rv rVCle
Flaming Gorge Model Results Comparison
Driest Three Year Cede Release Hyydr~graph
15D00 - - --
14000
-•Action Alternative -..
1300D -NoArtion alternative _
-
-
12aoa
11D00
10000 -- -
~ 9000
8000
°
-----
r~
7000
~ _-_
6000
5000
4000
300D
2000
1DDo
D
Jan-02 Jul-02 .Jan-D3 Jul-03 .Jan-D4 Jul-04 Jan-O5 Jul-05 Jan-06
Date
When conditions are wet, the Action and No Action alternatives operate Flaming Gorge
Dam very differently from when conditions are dry. Spring releases for the Action alternative in
wet years are typically larger than those generated for the No Action alternative as a result of
attempting to achieve specific targets established for Reach Two. This is evident in Figure 3,
which shows the reservoir elevations that occurred during the most intense three year wet cycle
found in the inflow hydrology. The higher releases that occur each spring under the Action
alternative cause the reservoir to fill less in the spring as compared to the No Action alternative.
As a result, the releases under the Action alternative during the baseflow period are not as high as
those that occur under the No Action alternative. The No Action alternative is forced to release
greater volumes during the baseflow period to achieve the drawdown target established for the
following year. This can be seen in Figure 4, which shows the daily release hydrographs that
occurred during this three year wet cycle. In November, the release constraints of the No Action
Figure 3 Reservoir Elevations Under the Most Intense Three Year Wet Cycle