8274

• UCREFRP Catalog Number: 8274
• Author: Pitlick, J. and R. Cress.
• Title: Longitudinal Trends in Channel Characteristics of the Colorado River and Implications for Food-Web Dynamics.
• USFW Year: 2000.
• USFW - Doc Type: Recovery Implementation Program Project 48-C,
• Copyright Material: NO

Combining the cross-section measurements of bankfull depth with reach-average values of slope
and grain size, we get corresponding estimates of the bankfull shear stress, rb, and the bankfull
dimensionless shear stress, r*b (Fig. 21). Over the full length of the study area, the rb decreases by
a factor of 3, from an average of 47 N/mZ in the uppermost reach to an average of 17 N/mz in the
lowermost reach (Fig. 21a). The high values of rb clustered around RKM 125 coincide with
Professor Valley. A least-squares fit of the full data set gives a weak exponential relation (R2=
0.16) with a slope of -0.0032. Over the same distance the median grain size decreases by a factor
of 2 (Table 1), resulting in a slight decrease in the z*b (Fig. 21b). This trend is subtle, however, and
the slope of the best-fit regression line is not significantly different from zero. For the reach as a
whole, the z'b averages 0.049. We emphasize the trend in r? because of its importance in sediment
transport relations. The consistency in r*b indicates that specific sediment transport thresholds are
likely to be exceeded in many places, providing some assurance that prescribed discharges will
achieve the desired effects on a widespread basis.
N
100
Z
co
N
N
d
L
U)
w
Y 10
c
cc
m
w 0.10
N
W
d
t
N
7
Y
C
m
0.01
a
•
0 0 0 •
?bo* 0• 00% o o o °o • •
• • ••
0 • • 00-'-•0-? 0 • •• • O
0 00 000000 ? .0 00 000 00
0 0 0 0 ••• 0-0o----01
o • 00 0 . .._
0 00 so
0
• •G 00
'` 0,00
T = 16.5'e o.aa3z•x ? 000
R2 = 0.16 00
0
350 300 250 200 150 100
b
•
ti •
0
0 08 • 0 00 • b 00 • •
0`O? A. O% O o O • • • 0 • N
0 0%---- 0 0? • •
NO N---------•-•------ 0 ---'0 -•••`-i -Y ? ------'p-Op ?---??----••-•?-'--
0 0 0 0m00 0 0 0 •• i • 0p 0 0 00 •
00 0 • 0 • %
0 0 •
= 0.046`e0.00013•x
R2 = 0.00042
350 300 250 200 150 100
Distance Upstream from Green River Confluence (km)
Figure 21. Downstream trends in (a) bankfull shear stress and (b) bankfull dimension-
less shear stress of the Colorado River. Symbols are the same as in Figure 20.
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