8188

• UCREFRP Catalog Number: 8188
• Author: Muth, R. T., et al.
• Title: Flow and Temperature Recommendations for Endangered Fishes in the Green River Downstream of Flaming Forge Dam.
• USFW Year: 2000.
• USFW - Doc Type: \
• Copyright Material: NO

Final Report

3-18

September 2000

Table 3.S.-Probabilities of exceedance for regulated and unregulated flows of the Green
River at the USGS stream gages near Jensen (Reach 2) and Green River, Utah (Reach 3),
1963-1996.

Flow at Jensen Gage Flow at Green River Gage
Probability of Recurrence (m3/s) (m3/s)
Exceedance Interval
(%) Years Regulated Unregulated Regulated Unregulated
50 2 448 669 575 788
20 5 618 934 836 1,132
10 10 727 1,076 1,003 1,321
5 20 827 1,192 1,158 1,477
100 1,045 1,396 1,495 1,753

Table 3.6.-Percent reduction in annual peak flows of the Green River due to regulation at
various exceedance values.

% Flow Reduction Due to Regulation at Various % Exceedance Values
River Reach/Gage 10 20 30 40 50 60 70 80 90
Reach lIGreendale -61 -73 -70 -67 -63 -61 -60 -58 -52
Reach 2/Jensen -32 -34 -34 -34 -33 -32 -30 -28 -23
Reach 3/Green River -24 -26 -27 -27 -27 -26 -25 -23 -19

The duration and timing of peak flows have also been reduced by regulation. Unregulated
flows of 475 and 575 m3/s are exceeded at the Jensen gage 8% and 4% of the time, respectively
(Figure 3.9). With regulation, however, these two flows are exceeded only 3% and 1 % of the time.
On average, peak flows now occur earlier in the year than they did before regulation. For both
Reach 2 and Reach 3, regulated peak flows generally occur about a week earlier than unregulated
peak flows (Table 3.7).

3.4.3 Base Flows in the Green River

Approximately 70% of the annual natural flow of the Green River occurs between April and
July as a result of melting snow. During the remainder of the year, natural flows are generally low.