7740

• UCREFRP Catalog Number: 7740
• Author: McAda, C. W. and L. R. Kaeding.
• Title: Physical Changes in the Gunnison and Colorado Rivers Resulting from Construction of the Aspinall Unit and Related Projects, with Hypotheses to Assess the Effects on the Endangered Fishes
• USFW Year: 1991.
• USFW - Doc Type: Final Report.
• Copyright Material: NO

Table 3. Percent decline of mean-monthly streamflow in the Gunnison
(Whitewater gage) and Colorado (Cisco gage) rivers during spring runoff
attributable to the Aspinall Unit. (Change from middle-development period to
post-Aspinall period.)
Month
Gunnison River
Change
Percent in
change CFS
Colorado River
Change
Percent in
change CFS
Percent of change
in Colorado River
due to Aspinall
April - 1.4 43.8 - 3.7 305.2 14.4
May -25.1 1,864.1 -12.8 2,477.3 75.2
June -32.2 2,326.7 -12.8 2,778.1 84.0
July - 2.6 62.6 + 8.6 699.4
(Table 3). Mean-monthly Colorado River flows have declined 2,477 and 2,778
cfs for the same months. Because changes in Gunnison River flow directly
affect Colorado River flow, the Aspinall Unit is responsible for 75 to 85~ of
the decrease in average spring runoff since 1966 for the Colorado River at
Cisco (Table 3).
EFFECT OF CHANGES CAUSED BY THE ASPINALL UNIT ON THE ENDANGERED FISHES
Water Temperature
The Aspinall Unit reduced the temperature of the Gunnison River within
historic range of Colorado squawfish and razorback sucker. This temperature
reduction probably did not affect adult habitat, but may have affected
maturation of adult fish or spawning success--particularly of Colorado
squawfish. Pre-Aspinall temperatures in the lower Gunnison River were already
marginal for Colorado squawfish reproduction, but construction of the Aspinall
Unit reduced them further. Wiltzius (1978) suggested that construction of the
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