8112

• UCREFRP Catalog Number: 8112
• Author: Osmundson, D. B. and B. K. Scheer.
• Title: Monitoring Cobble-Gravel Embeddedness in the Streambed of the Upper Colorado River, 1996-1997.
• USFW Year: 1998.
• USFW - Doc Type: Grand Junction, CO.
• Copyright Material: NO

Table 1 continued.
Mean
Median
Habitat-Bank
Run-U per 67.2 61.5
Riffle-Upper 61.0 55.9
P S NS
Run-Lower 85.9 82.2
Riffle-Lower 84.4 79.8
P NS NS
Run-Upper 67.2 61.5
Run-Lower 85.9 82.2
P S S
Riffle-Upper 61.0 55.9
Riffle-Lower 84.4 79.8
P S S
locations) were very similar to those taken during base flow (lower banks): 123 mm during
runoff, 126 mm during base flow. Although these differences were statistically significant,
the differences were so slight as to probably have no biological importance. The largest
difference we noted was between runs and riffles. Depth-to-embeddedness was slightly
greater in the riffles: 129 mm for rifles versus 119 mm for runs. These differences were
more acute in 1996 than in 1997 (Table 2).
Comparisons Among Dates Within Runoff and Base-flow Periods
Runoff. In 1996, total DTE significantly increased from the first to the second sampling date
in riffles of strata 9 and 8 and also in runs of Stratum 9. This pattern was repeated in 1997,
but only in riffles of Stratum 9 (Table 3 and Figures 8 and 9). Between the second and third
runoff sampling date in 1996, DTE significantly decreased in runs of both strata, though not
in riffles. This pattern was not seen in 1997: then, DTE remained essentially constant
between the second and third sampling dates in both habitats in both strata.
An additional riffle site was added in the 15-mile reach in 1997 (Riffle 1-B in reach 9-B) at a
bar in which declining runoff flows were eroding small chute channels at right angles from the
direction of the main-channel flow. On a given date, there were 3-4 of these small chutes
actively dissecting the bar with water pouring into a secondary channel situated parallel to but
at a lower elevation than the adjacent main channel. Tertiary bars of eroded gravel and
cobble formed at the base of these chutes. By the end of the runoff season, about a dozen of
these chutes had formed; the now-dry chutes were clustered parallel to one another and were
confined to the center region of the bar, evidently having formed only during a narrow range
of flows. We sampled depth-to-embeddedness in two of the chutes when they were active:
17