7145

• UCREFRP Catalog Number: 7145
• Author: Inslee, T. D.
• Title: Spawning of Razorback Suckers
• USFW Year: 1981.
• Copyright Material: NO

the past 24 years, peak flows have been less than this 58% of the time.
During the low water years of 1988 and 1989, when the abundance of intro-
duced minnows greatly increased, peak flows at the State line were 15,000
and 9,480 cfs, respectively. Peak flows of 15,000 cfs or less at the State
line now occur at a rate of about 25%, or an average of once every four
years (Fig. 8). We believe the now-common occurrence of these low-flow
years has greatly aided the proliferation of these introduced fishes.
In determining optimal flows for the 15-mile reach we need to consider not
only the habitat affected within the reach itself but also the contribu-
tion that flows there make to the Colorado River downstream. Though the
Colorado River picks up substantial inflow from the Gunnison River, the
majority of Colorado River flow downstream of the Grand Valley is com-
prised of upper Colorado and not Gunnison River water (Fig. 9 and Appendix
30,000
COLORADO (15-MILE)
25,000
U
W 20,000
1-
0- 15,000
U
00
U 10,000
5,000
0
APR MAY JUN APR MAY JUN
HISTORIC RECENT
Figure 9. Recent and historic mean monthly flows in the Colorado River
at the top of the 15-mile reach and in the Gunnison River near Grand
Junction, Colorado. Data from Table 5.
32