9676

• UCREFRP Catalog Number: 9676
• Author: U.S. Department of the Interior.
• Title: Preliminary Analysis
• USFW Year: 2001.
• USFW - Doc Type: Wayne N. Aspinall Unit Operations and the Draft Endangered Fish Flow Recommendations for the Gunnison and Colorado Rivers.
• Copyright Material: NO

Attachment B contains the following summary tables from the hydrology runs:

B-1 Peak Flows, Gunnison River below Gunnison Tunnel (Black Canyon)
B-2 Peak Flows, Gunnison River at Delta
B-3 Peak Flows, Gunnison River near Grand Junction (Whitewater)
B-4 Blue Mesa Reservoir, End-of-Month Elevation
B-5 Blue Mesa Reservoir, End-of-Month Content
B-6 Average Monthly Flows, Gunnison River below Gunnison Tunnel (Black Canyon)
B-7 Average Monthly Flows, Gunnison River near Grand Junction (Whitewater)

Peak Flows

Peak flows are needed for habitat maintenance. The recommended minimum peak flows at the
Whitewater gage for endangered fish vary according to the type of hydrologic runoff. The
recommended peaks consist of a minimum 2 day peak with a flow of 90 percent of the peak on the
previous day and the following day. The peaks for each year for each of the 4 model runs are shown
in Table B-3 in the attachments. The following table shows the percent of time when the modeled
peak flows exceeded 95 percent, 80 percent, 75 percent and 70 percent ofthe recommended minimum
peak flow,

95% of Recommended Min. Peak
90% of Recommended Min. Peak
80% of Recommended Min. Peak
75% of Recommended Min. Peak
70% of Recommended Min. Peak

Percent of Years Peak Exceeded
Run A RunB
Baseline FWS 5000
19 35
19 50
27 81
46 92
58 100

Rune
FWS 6500
35
58
85
96
100

RunD
FWS UNL TD

35
58
85
96
100

An analysis of these results indicate that using the spillways at Morrow Point (Model Run D) with the
current operation criteria provides no real advantage to meeting the recommended minimum peak
flows. A detailed look at the specific flows show use of Morrow Point spillways would result in an
additional 300 cfs in one year; therefore, it must be concluded that physical limitations at Blue Mesa
Reservoir upstream prevented any additional release. The use of the bypass outlet of Morrow Point
(Model RunC) has only a small benefit. Using the bypass increased the peak flow in 8 years, in 3 of
those the increase was less than 100 cfs. The increases in the other 5 years were 350, 350, 500, 700,
and 1,500 cfs. In two of these instances, the increases were limited due to physical constraints of the
outlet works at Blue Mesa. Blue Mesa's spillway is unavailable to make releases when the reservoir
water elevation is below the spillway crest.

It should be noted that even though 90 percent of the recommended peak flow at the Whitewater gage
was met only 58 percent of the time when using Morrow Point bypass outlets or bypass outlet plus
spillway, the Aspinall Unit releases met the FWS demand hydro graph peaks in all but 3 years. In 2 of
these 3 years, the physical limitation of the Blue Mesa outlets prevented additional releases; and in
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