a. Low concentration of ice.
b. Moderate concentration of ice.
Figure 21. Model ice moving through the alluvial channel fitted with border ice.
sweep fully across the confluence by water cur-
decreased with increasing ice discharge (or sur-
rents alone, and therefore does not jam. However,
face concentration of ice) issuing from the Missouri
field observations show that ice drifting from the
River. In a corresponding manner, and somewhat
Missouri River does sweep across the Mississippi
surprisingly, the amount of ice swept across the
River at the confluence, as Figure 22 depicts. This
confluence also diminished as the areal concen-
difference suggests that other factors need to be
tration of model ice increased. Essentially, a more
considered, i.e., wind, border-ice growth, bathy-
compact layer of moving ice increasingly damped
metric complexity, such as a large dune at the
surface eddy formation.
confluence, or a channel contraction downstream
A related, preliminary finding is that ice dis-
of the confluence. During tests, some model ice
charge category I.1 probably does not lead to jam-
dispersed across the confluence through the
ming, unless other factors, such as described
action of the large eddies at the shear layer be-
above, prevail.
tween the merging Missouri and Mississippi
As wind often significantly affects ice drift in
flows. The visible size of the eddies at the surface
wide channels, a brief qualitative test was con-
26
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