Figure 31. Flow impact holds ice in channel 2.
ice runs in question be near the ice conveyance capacity of the particular channels.
The additional force associated with the merging of ice and water equals or
exceeds the force increment needed to cause ice to jam in the confluent channel.
1. Jamming of merging ice runs
The first mechanism suggests the following criterion for use in assessing
whether a jam will develop in one or other of the two confluent channels entering
the confluence: ice moving in one confluent channel will jam if
ΣF F′merge1 1F″merge1 = Fdrag + Fweight Fbank
Fstrength F′merge1 1F″merge1 ≤ 0
(21)
where Fdrag
=
water drag force acting against the ice,
Fweight
=
the streamwise component of weight of the moving ice,
Fbank
=
bank friction acting against the ice in channel 1,
=
the internal strength of the ice.
Fstrength
These four forces are usual for ice jams in single channels. The further forces are
F′merge1 = σz2η2(bd) and F″merge1 = σz2η2(b2/sinα + be). The force F′merge1 is approx-
imated as the lateral pressure exerted by ice moving from channel 2, σz2, multi-
plied by the contact area normal to the direction of flow in channel 1, η2bd. The
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