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<br />5
<br />
<br />National Monument, was located from rm 328.5 to 334.5 (6.0 miles); the
<br />Jensen site, just below Split Mountain, was located from rm 303.0 to 310.0
<br />(7.0 miles); the Ouray site, in Ouray National Wildlife Refuge, was located
<br />from rm 250.5 to 261.5 (11.0 miles); the Sand Wash site, below the Ouray
<br />site, was located from rm 222.5 to 225.5 (3.0 miles), and the Mineral Bottom
<br />site, about 50 miles above the confluence of the Colorado and Green Rivers,
<br />was locat~d from rm 51.0 to 57.0 (6.0 miles). RH designations were as
<br />previously discussed.
<br />
<br />Backwater numbers and area were examined during seven riverf10ws at the
<br />Island Park, Jensen, OuraYj and Sand Wash sites: 5,260, 2,423, 1,773, 1,687,
<br />1,430, 1,381, and 1,101 ft Is. Figure 2 presents the average daily flow at
<br />the Jensen gauge from June to November for 1987 and 1988. Backwater numbers
<br />and area were examined during three flows at the Mineral Bottom site: 3,814,
<br />3,261, and 2,748 ft3/s. Flow measurements for the four upper sites were
<br />taken at the Jensen USGS gauge, and the Mineral Bottom flow measurements
<br />were taken at the Green River USGS gauge. When flows were stabilized at
<br />each site, color infrared aerial photography was acquired at an approximate
<br />scale of 1:4,000. Flows were gradually stepped down during the late spring
<br />and summer in order to mimic the descending limb of a "natural" Green River
<br />hydrograph. However, because of weather conditions, the 1,430 ft3/s flow
<br />was not photographed in proper sequence and was actually the last flow
<br />attained.
<br />
<br />Field trips were taken to familiarize the photointerpreter with backwater
<br />delineation and to place panel markers at specified distances at each site
<br />to verify and correct photographic scale. Aerial photographs were fitted
<br />with mylar overlays upon which the river channel, backwaters, and sandbars
<br />were delineated. Transfer and digitization processes were as previously
<br />described.
<br />
<br />Backwaters were classified according to their position in the river. Bank
<br />backwaters occurred in sandbars or cobblebars attached to the bank, and
<br />channel backwaters were associated with sandbars or cobblebars in mid-
<br />channel. Bank and channel backwaters were further separated according to
<br />area: <20, >20<200, >200<500, >500<1,000, and >1,000 m2.
<br />
<br />Regression analyses (Bailey 1981) were conducted for flow versus backwater
<br />area and flow versus backwater number at each site. linear re~ression of
<br />flow versus area was analyzed for flows from 2,423 to 1,101 ft /s for the
<br />Island Park, Jensen, and Ouray sites. The 5,260 ft3/s flow was deleted
<br />because it was far outside the range of normal operations and was not
<br />considered a realistic flow scenario for the summer season. The 1,430 ft3/s
<br />flow was also deleted at the Sand Wash site, as this flow had not reached
<br />the site when the photography was acquired.
<br />
<br />1988 Study
<br />
<br />Approximately 320 rm from about rm 335 to rm 0 (confluence of the Green and
<br />Colorado rivers) were photographed during 1988. Because of the length of
<br />the river being studied, CIR photography was obtained at an approximate
<br />scale of 1:6,000 on August 23, 27, and 28. The 1:6,000 scale photography
<br />
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