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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16
Typically, by the end of July, theOreservoir is approaching its highest level of the year.
Figures 9 and 10 show the same relationships as Figures 7 and 8, only for reservoir elevations at
the end of July. Inspection of these figures shows again that the occurrences of elevations at the
end of July that were below 6000 feet above sea level increased significantly when the model
achieved the 18,600 cfs objective. The Action(ALL-l) occurrences when elevations at the end of
July were below 6000 were about 20 (> I % ofthe time). The Action(ALL) occurrences for this
same classification were nearly 300 (12% of the time). The No Action model run had no
occurrences where elevations at the end of July were below 6000.

Table 2 shows the exceedance percentage values for all February and July elevations for
the Action(ALL and ALL-I) and No Action results. The results in Table 2 indicate that the
"most likely" (50% exceedance) reservoir elevations at the end of February for the Action(ALL-
I) model run were be about 2 feet lower than the No Action model run. The "most likely" end of
July elevations had a difference of nearly 4 feet for the Action(ALL-l) and NoAction rulesets.
Similar comparison between the Action(ALL) ruleset and the NoAction rulesets shows that the
"most likely" end of February elevations were about 5 feet lower for the Action(ALL) then the
NoAction ruleset. The July elevation difference was about 7 feet.

TABLE 2 P

t E

d

Fb

/J I EI f

ercen ~e xcee ance e ruarYI my eva IOns
Percentage A9tion (ALL-I) Action (ALL) No Action
Exceedance (Feet above Sea Level) (feet above Sea Level) (Feet above Sea Level)
90% 6016.4/6019.2 5992.9/5997.2 6020.1/6021.4
80% 6020.116023.6 6013.7/6015.7 6024.7/6024.1
70% 6022.5/6026.4 6017.7/6020.3 6026.3/6026.7
60% 6024.0/6028.0 6020.0/6023.5 6026.9/6028.7
50% 6025.116029.1 6022.0/6026.0 6027.0/6032.8
40% 6025.9/6030.3 6024.2/6027.9 6027.2/6033.9
30% 6026.3/6030.7 6025.5/6029.3 6027.3/6034.9
20% 6026.6/6031.2 6026.2/6030.8 6027.5/6036.1
10% 6027.0/6032.1 6026.8/6031.8 6027.7/6038.0

Figures 11 and 12 show the complete distribution of the February and July elevations that
were predicted for the three model runs. For reference, historic elevations for the period from
1971 through 1991 have been included on the figures.