7245

• UCREFRP Catalog Number: 7245
• Author: Rose, K. L. and D. R. Hann.
• Title: Consolidated Instream Flow Report, Habitat Modeling on the Green River Using the Physical Habitat Simulation System.
• USFW Year: 1989.
• USFW - Doc Type: Grand Junction, Colorado.
• Copyright Material: NO

3. Calculation of WeiQhted-Usable-Area

The objective at the Ouray site was to quantify changes in backwater habitat
for young-of-year Colorado squawfish. Presently, the only curve available for
young-of-year was developed by Bio/West, Incorporated (Valdez et al., 1987;
Figure 10) and applies to the Upper Colorado River System occupied by Colorado
squawfish from March to November. Pucherelli et al. (1989) reported that a
range of flows between 1100 and 1800 cfs (measured at the Jensen Gage)
produced substantially more backwater area and numbers in the upper Green
River. Further it has been noted from field observations (Tyus, H. personal
communications) that flows at Ouray above 3200 cfs inundate all mid and side
channel backwaters thus eliminating the important nursery habitats. For these
reasons, we simulated flows from 1000 to 3200 cfs only for young-of-year at
Ouray study site.

At the Ouray study site, PHABSIM predicts that the WUA for young-of-year
squawfish was maximized at a flow of 1200 cfs, with an approximate 90 percent
habitat retention level with a flow range between 900 and 1300 cfs (Table 23).

Table 23. Weighted-usable-area (WUA) versus simulated discharges for young-
of-year Colorado squawfish at the Ouray site on the Green River,
River Mile 259.0.

------------------------------------------------------------------------------

WA

Discharge
in cfs

Young-of-Year Colorado Squawfish
March/November

1000.00
1200.00
1400.00
1600.00
1800.00
2200.00
2400.00
2600.00
2800.~0
3000.00
3200.00

6080.62
6403.91
5192.13
4368.83
3788.50
3259.12
3983.41
4934.37
4865.26
5045.51
5446.42

4. Discussion

This analysis has, at this time, a severe restriction in that the frequency,
distribution, or variability in size of side channel backwaters, or the range
of flows when backwaters become chutes or isolated pools is unknown.

36