84
ERDC/CRREL TR-02-14
north bank along the site. With further flow the deposited sediment may eventu-
ally erode until the thalweg is lowered to the elevations reached during winter.
Away from the thalweg, the bed along the river's south side rose, typically
by about 23 ft. This was likely caused by sediment deposition resulting from the
reduced flow velocities through that portion of the river. The bed seems not to
have eroded back to a lower elevation once the ice cover had broken up.
Flow velocity
A velocity profile about the middle of the channel at ice station 2+00 with
respect to the north bank is shown in Figure 60. The winter stations were repeat-
able in location, and the open water measurements were within a 15-ft radius.
But because they were not at precisely the same location, the open water meas-
urements could have skewed the plot because of the dramatic changes of the bed
elevation in the area.
1900
1895
1890
1885
1880
Oct-98
1875
Jan-99
Feb-99
1870
Apr-99
1865
Location: Approximate center of the thalweg at RM 1624.02
1860
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Velocity (ft/s)
Figure 60. Velocity distributions at approximately mid-channel at RM 1624.02.
Comments
Of all the sites monitored, this site had by far the largest extent of channel
shifting and bank erosion during, and immediately subsequent to, ice cover
formation.
An interesting feature of riverbank behavior observed at this site was the
gradual tilting of the face of the site's concave bank. As winter progressed,
cracks along the bank top widened, and strips appeared to peel slowly from the
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