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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Reach One Spring Peak Release Results

18

The estimated flows at all points along Reach One were assumed in the model results to
be the same as the release rate from Flaming Gorge Dam. During the spring, the model released
the volume of water necessary to safely operate the reservoir while also achieving the objectives
of the Action (ALL and ALL-I) and NoAction alternatives. Figure 13 shows the distribution of
the peak flows (greatest magnitude single day average flow) that occurred in Reach One for all
three model runs. The capacity of the power plant at Flaming Gorge is assumed to be 4600 cfs.
Releases greater than 4600 cfs are considered bypass releases. Figure 13 shows that water was
bypassed by the No Action model run in about 18% of all years. The Action (ALL-I) model run
bypassed water in about 37% of all years while the Action (ALL) model run bypassed water in
about 53% of all years. It is also noted that bypasses from the Action (ALL and ALL-I) model
runs had significantly higher magnitudes than those for the No Action model run. For reference,
historic peak flows for the period from 1971 to 1991 are included in Figure 13. This historic data
includes years 1983, 1984, and 1986, which were abnormally wet years in the Upper Green River
Basin. Statistically, it is very unlikely that three years of such high magnitude would occur
within 20 years of record. The historic record presented in Figure 13 is therefore statistically
skewed toward wet conditions. Figure 13 also shows that the differences in peak releases
between the Action (ALL) and the Action (ALL-I) model runs were significantly larger than the
differences between the Action(ALL-l) and No Action model runs.

FIGURE 13 Distribution of Peak Flows in Reach One

14000
12000
10000
~ 8000
~
~
~
0
u: 6000
4000
2000

Flow Durations (May - July)

Reach I

- - No Action Peak Flow
- Historic Peak Flow (71-9 I )
- All - 1 Peak Flow
I - All Peak Flow
I- ~
- I
-, I-- ~
'-- L I ~
I L- h
I I
I
1.-
'---

o
0%

40% 60%
Percent Exceeded

80%

100%

20%