Figure 21. Ice in confluence: Q2/Q1 = 2/3, α = 90,
Figure 22. Ice in confluence: Q2/Q1 = 3, α = 90, and
and b1/b2 = 1.5, bathymetry modeled.
b1/b2 = 1.5, bathymetry modeled.
Figure 23. Ice in confluence: Q2/Q1 = 3, α = 90,
and b1/b2 = 3.
vealed that the available surface area for ice movement through the conflu-
ence was much reduced. Also, the flow from channel 2 was necked more tightly
than was the case without the bar. Jamming on channel 2 not only occurred
quicker, but it occurred with a lesser ice transport rate than for the preceding
example. Figure 21 illustrates ice jammed in channel 2.
Case 4: Q2/Q1 = 3; b1/b2 = 1.5; b2 = 16 cm; bar modeled. This example further
shows that the presence of a bar in the confluence exacerbates ice jamming.
Increased discharge on channel 2, together with a bar present, rapidly caused
a jam to form in channel 1, as illustrated in Figure 22. The jam was more severe
in this case compared to Case 2 above, because the confluence region avail-
able for ice conveyance was reduced.
Case 5: Q2/Q1 = 3; b1/b2 = 3; b2 = 16 cm. This example illustrates the influence
on ice movement of widening of the main channel (i.e., decreasing bd/b3, while
retaining Q1/Q2). For the same discharge conditions as for the first example,
the widened confluence was able to convey ice from channel 1 without jam-
ming. Even though the greater width of channel enabled the dividing stream-
line to extend further into the main channel than was the case with the nar-
rower main channel, jamming occurred as evident in Figure 23. Note the model
ice pieces trapped in the separation zone indicate the extent of that zone.
33
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