WSP05167

• File Number: 8220.104.I
• Description: Flaming Gorge
• State: UT
• Basin: Yampa/White/Green
• Date: 10/1/2001
• Author: Clayton-Gilmore
• Title: Flaming Gorge Environmental Impact Statement Hydrologic Modeling Study Report
• Water Supply Pro - Doc Type: Report/Study

26

Reach Two Base Flow Release Results

Figure 23 shows the distribution of Reach Two flows during the base flow period that
occurred in the three model runs, Jensen gage Pre-dam historic flows (1950-1961) during the
base flow period and Jensen gage post-dam historic flows (1971-1991) are also shown in the
figure, The historic flows prior to 1961 show the distribution of flows in Reach Two during the
base flow period prior to the construction of Flaming Gorge Dam, Historic flows during the
period from 1971 through 1991 show the distribution of Reach Two flows after the construction
of Flaming Gorge Dam but prior to the 1992 Biological Opinion, The most significant change
that has occurred in Reach Two in terms of river regulation occurred during the period from the
end of the construction of Flaming Gorge Dam to 1991. Reach Two flows during the base flow
period were elevated substantially as a result of power production at Flaming Gorge Dam, The
No Action curve, shows the distribution of Reach Two flows during the base flow period that as
a result of operating Flaming Gorge Dam to achieve the flow objectives of the 1992 Biological
Opinion. The Action(ALL and ALL-I) curves show how the Action Alternative would adjust the
current distribution, Most notably the Action Alternative operational regime depressed the flows
during the base flow period in Reach Two when conditions are wetter than average in the Upper
Green River Basin,

FIGURE 23 Exceedance Percenta e Flows for Reach Two Flows Durin Base Flow Period

Base Flows - Reach Two
August through Febuary

5000

No Action
-f-AIl-I
All
-II- Historical (71-91)
* Pre Dam (50-61)

4000

~
~
""

3000

..
o
ti:
2000

1000

9J%

20%

40% 60%
Percentage Exceedance

80%

100%