9553

• UCREFRP Catalog Number: 9553
• Author: Valdez, R. A. and R. T. Muth
• Title: Ecology and Conservation of Native Fishes in the Upper Colorado River Basin
• USFW Year: 2005
• USFW - Doc Type: American Fisheries Society Symposium
• Copyright Material: YES

174

VALDEZ AND MUTH

150 m3/s to nearly 800 m3/s. Closure of Glen Can-
yon Dam in spring 1963 interrupted river flows, and
dam releases no longer reflect natural flows.
Mean daily flow for the Green River at Green
River, Utah (1923 and 1997) reflects changes to sea-
sonal flow patterns as a result of human activities in
the upper basin (Figure 6). Average peak flows of the
Green River in June have decreased by 31 % (631 to
433 m3/s) and base flows in January have increased
by 81 % (48 to 87 m3/s). Average peak flows of the
upper Colorado River near Cisco, Utah, in June have
decreased by 30% (759 to 530 m3/s) and average
base flows in January have increased by 40% (72 to
101 m3 / s). These changes in stream hydrology have
affected various parts of the river ecosystem on which
the native fauna and flora depend.

Physical Habitat Destruction, Alteration, and
Fragmentation

Dams, diversions, and local channelizations account

for most aquatic habitat destruction or modification

1400
1200
1000
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C') 800
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J 600
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400

in the upper basin. Nine dams impounded major
rivers or tributaries of the upper basin starting in
1962 and inundate a total of about 940 km of river-
ine habitat. These dams, years of completion, and
length of inundation are: Glen Canyon Dam (1963,
325 km of the upper Colorado River), Flaming Gorge
Dam (1964, 265 km of the Green River), Navajo
Dam (1962, 120 km ofthe San Juan River), Aspinall
Unit (i.e., Blue Mesa, Crystal, and Morrow Point
dams; 1965, 60 km of the Gunnison River), Taylor
Draw Dam (1984, 60 km of the White River),
McPhee Dam (1984, 80 km of the Dolores River),
and Fontenelle Dam (1964, 30 km of the Green
River). These dams have also disrupted the river con-
tinuum and converted about 300 km of seasonally
warmed river reaches into cold, isothermal tailwaters.
Dams have fragmented habitats, blocked passage of
migrating fish, reduced high channel reshaping flows,
and increased base flows. Local channelizations for
highway construction, flood control, and community
development have straightened the river channel, fur-
ther reducing habitat diversity.

200
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ns II) I.'G CI. :s :s :::s II) u 0 lD
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Figure 6.-Daily historic and recent flows for representative years of similar flow volume for the Green River at
Green River, Utah. U.s. Geological Survey stream gage data.