94
ERDC/CRREL TR-02-14
1930
Dec
1925
Jan
Feb
1920
April
1915
1910
1905
1900
1895
0
100
200
300
400
500
600
700
800
900
Distance Relative to Downstream Left Bank (ft)
Figure 67. Bed profile cross sections at RM 1646.9.
Flow velocities
Variations in the velocity profile approximately midchannel of the upstream
cross section are shown in Figure 68 (RM 1649.90 station 5+00). Velocity
measurements were not taken during the open water survey in April.
Comments
The survey revealed important glimpses into the dynamic nature of ice cover
interaction with the multiple subchannels of a sinuous-braided channel. However,
this site also revealed the considerable extent to which ice cover effects on chan-
nel stability are inadequately understood.
The survey was only partially successful in detecting the ways in which river
ice influences channel stability at the Mattelin site. As with the Culbertson site
the major changes in bed profiles are related to the process by which the ice
cover formed and progressed upstream through the site. The dynamic manner in
which that process unfolded at the Mattelin site was difficult to monitor by
means of intermittent bathymetric surveys of the site; site monitoring inevitably
was fragmentary. Though the bed profiles are useful, an alternate approach to
monitoring is required. For example, a useful alternative approach may be based
on bathymetric surveys of the site before and after ice cover presence and on
aerial photographs or video taken of the site as the ice cover forms.
Throughout the winter the exposed and partially vegetated face of the north
bank of the site desiccated through freezethaw and sublimation, and spalled
bank material fell onto the ice cover below (Fig. 69). This desiccation weakened
the bank face, making it prone to erosion by ice and water.
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