7246

• UCREFRP Catalog Number: 7246
• Author: Pucherelli, M. J. and R. C. Clark.
• Title: Memo - February 9, 1990, Green River Backwater Habitat Mapping; Fluctuating Flow Test, Utilizing Airborne Videography Techniques ‎(Endangered Fish)‎.
• USFW Year: 1990.
• USFW - Doc Type: Denver, Colorado.
• Copyright Material: NO

4

Jensen

There were 26 backwaters at the Jensen site on August 2 (table 2) with a
total of 10,870 m2 (flow = 1,515 ft3/s). Subsequent to fluctuating flows,
backwater number increased to 34, but, backwater area remained stable
(10,941 m2) on August 16. Stabilized flows for 6 weeks increased backwater
area by 36 percent to 14,930 m2 on September 28, although backwater number
decreased to 30.

Backwater area decreased by about 50 percent to 7,593 m2 on October 11, and
backwater numbers decreased similarly. The same concerns discussed above
for this date and flow apply here.

Ouray

There were 37 backwaters at the Ouray site on August 2, with a total area of
35,098 m2 (flow = 1,500 - 1,700 ft3/s). Following the fluctuation of flows,
the number of backwaters remained similar (33) while backwater area
decreased about 13 percent to 30,482 m2 on August 16. Subsequent to stable
flows for 6 weeks, backwater number increased by approximately 70 percent,
to 56, and backwater area also increased by 70 percent, to 51,824 m2 on
September 28 (flow = 1,420 ft3/s).

The October 11 backwater number decreased substantially, to 29, as did
backwater area, to 37,898 m2 (flow = about 2,500 ft3/s). The flow on this
date was significantly higher than on the previous dates that video was
collected, which probably had an impact on backwater habitat.

Discussion

It is apparent that the flows on October 11 were higher than anticipated and
that they had a significant, negative impact on backwater habitat. At each
site studied, this flow produced the fewest backwaters and the least
backwater area. Although these data cannot be used in the fluctuating flow
study, it is notable that the flow on this date (about 1,900 ft3/s) is
outside the range recommended by the 1987 study for optimum backwater
availability (Pucherelli et al., 1988), of 1,100 to 1,800 ft3/s at the
Jensen gauge on the Green River.

There are two comparisons that may be made with the remaining three video
events, (1) video results between August 2 and August 16, which reflect the
effect of daily flow fluctuations between 1,600 and 2,900 ft3/s, and
(2) video results between August 16 and September 28, which reflect the
effect of very stable daily flows.

Fluctuating flows of 1,600 to 2,900 ft3/s produced a substantial decrease in
backwater area only at the Island Park site. A smaller decrease was
recorded at Ouray, while backwater habitat at Jensen remained relatively
unchanged following this event. The decrease in backwater habitat at