9602

• 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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In the 65 traces of inflow hydrology used to populate the model, a variety of wet and dry
cycles occurred. These cycles were routed through the Flaming Gorge model with the reservoir
elevation set at various levels to show the full range of potential impacts that could realistically
occur. The cycles having the driest and wettest intensities with durations of two, three, five, and
seven years were found in the model results. The traces where these cycles occurred at the
beginning of the trace were identified so that the differences between the Action and No Action
alternatives could be directly compared. This is because the water surface elevation of the Action
and No Action alternatives were the same in these traces prior to these cycles routing through
Flaming Gorge Reservoir. The difference in reservoir elevation at the end of the cycle then could
be attributed solely to the operational regime. The reservoir elevations and release hydrographs
generated under the Action and No Action alternatives were plotted to show the differences
between these regimes. Figure 1 shows the reservoir elevations resulting from the most intense
three year dry cycle found in the input hydrology. The plot extends one year beyond the end of the
dry cycle to show the rate at which the reservoir was able to recover under the two alternatives.
Fia„rP 1 Re.cPrvnir F.levntinnc Ilnder the Most Intense Three Year Dry Cycle
Flaming Gorge Model Results Comparison
Driest Three Year Cvde Elevations
6050 - -
6045
6040
6035
--
6030
6025
0
6020
N
W
6015
6010 -
6005
-Action .alternative
6000 -
-NoActinn Alternative
-
5995 ---
5990
Jan-02 li_tl-02 Jan-03 Jul-03 Jan-04 Jul-04 Jan-05 Jul-05 Jan-06
Date
By the end of this three year cycle, operating under the No Action alternative caused the
reservoir elevation to be about eight feet lower than operating under the Action alternative. This
can be mostly attributed to the fact that the No Action alternative requires a spring peak each year
with a minimum duration of seven days while the Action alternative allows the spring peak to with
a duration as short as two days. The corresponding release hydrographs produced for this three
year cycle are shown in Figure 2. While the peaks, under both alternatives, have a magnitude of
4600 cfs (power plant capacity), the No Action alternative maintains 4600 cfs for seven days
before declining back to baseflow levels where as the Action alternative peaks for only two days.