9670

• UCREFRP Catalog Number: 9670
• Author: Pitlick, J.
• Title: Channel Monitoring To Evaluate Geomorphic Changes On The Main Stem Of The Colorado River.
• USFW Year: n.d.
• USFW - Doc Type: Boulder, CO.
• Copyright Material: NO

As the plots on the preceding page show, the flow depth through the study reach
increases rapidly over the range of low to intermediate discharges, and more slowly thereafter. It
is also evident that the water-surface profile becomes more uniform as the depth and discharge
increase. The adjustments in depth and slope both influence changes in boundary shear stress, T,
which are used as the basis for estimating thresholds for bed load transport. Recall that the
boundary shear stress is calculated using equation 3, with the observed depth, h, and the modeled
energy slope, Se. Figure 25 plots the modeled values of boundary shear stress versus discharge
for the range of observed flows. The individual points represent the modeled values of boundary
shear stress at each of the cross sections in the study reach, and the smooth curve represents the
best-fit relation.

45

40
35
= • = s •
N

? 30 •

25

U)20 •
cc 15
v ? y _ 2.932 .ao
? 1 0
5 • • R2 = 0.51

0

0 100 200 300 400 500
Discharge (m3/s)
Figure 25. Relation between shear stress and discharge, RM 176
The results shown above indicate that, for a given discharge, the shear stress can vary
appreciably from one cross section to another. The greatest range in shear stress occurs at a
discharge of 125 m3/s, which was the second lowest discharge modeled. At this discharge, all of
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