|
<br />2
<br />
<br />cost-effective alternative for mapping backwater availability using
<br />videography was investigated during 1988 (Pucherelli et al., 1989). The
<br />study found that the quality of videography was sufficient to replace aerial
<br />photography for use in river monitoring studies.
<br />
<br />The objective of the study presented here was to determine the effects of
<br />fluctuating flows on backwater habitat at three sites in the Green River
<br />using airborne video.
<br />
<br />Methods
<br />
<br />Three study sites were selected by FWS and Reclamation in areas known to
<br />contain important backwater habitat for young-of-the-year Colorado
<br />squawfish: the Island Park site, just above Split Mountain in Dinosaur
<br />National Monument--river-mile (r-m) 328.5 to 334.5 (about 6 miles); the
<br />Jensen site, just below Split Mountain, located from r-m 303.0 to 310.0
<br />(7 miles); and the Ouray site, located in Ouray National Wildlife Refuge,
<br />from r-m 250.5 to 261.5 (11.0 miles). River-mile designations were from
<br />Evan's and Belknap's Dinosaur River Guide. Video was acquired at each site
<br />on four dates: August 2 (flow = 1,515 ft3/s), August 16 (flow =
<br />1,500 ft3/s), Segtember 28 (flow = 1,420 ft3/s), and October 11, 1989
<br />(flow = 1,900 ft3/s).
<br />
<br />Two fluctuating flow events were analyzed: (1) Stable flows at Jensen were
<br />maintained for most of July to allow backwaters to form under a "normal II
<br />summer hydrograph, and video was acquired on August 2. Following this
<br />sequence, releases from Flaming Gorge Dam produced fluctuating flows at the
<br />Jensen gauge, beginning on August 7, ranging daily from approximatell 1,600
<br />to 2,900 ft3/s until August 14. Flows were reduced to about 1,500 ft /s on
<br />August 15 and 16 and remained stable, and a video of each site was acquired
<br />on August 16. (2) Stable daily flows were maintained at the Jensen gauge
<br />from August 16 to September 28, with little variation in daily or weekly
<br />flows. Flows were generally about 1,000 ft3/s or less from August 23 to
<br />September 27. On September 28, flows were increased to about 1,420 ft3/s
<br />and video was acquired. Following this stable flow sequence, flows were
<br />again fluctuated beginning October 4 through October 11. Daily flows at the
<br />Jensen gauge ranged from about 1,600 to 3,700 ft3/s. Video was acquired on
<br />October 11 for each of the sites as described above. The flow at the Jensen
<br />gauge was expected to be between 1,400 and 1,500 ft3/s on October 11
<br />(see enclosed letter dated July 27, 1989, from Reclamation to WAPA);
<br />however, when the video was acquired, the flow was about 1,900 ft3/s. Thus,
<br />backwater area at the three sites cannot be successfully compared between
<br />September 28 and October 11 because the flows on these dates (1,420 and
<br />1,900 ft3/s were substantially different and would produce different amounts
<br />of backwater habitat regardless of antecedent flows.
<br />
<br />The above flow scenarios allow the following comparisons at Island Park,
<br />Jensen, and Ouray sites, Green River: (1) The effects of fluctuating flows
<br />of 1,600 to 2,900 ft3/s on backwaters formed under stable flow conditions,
<br />(2) the effects of stable flows, for about 6 weeks, on backwaters between
<br />
|