5
DESIGN OF ICE BOOMS
m/s) for the maximum velocity. Ice retention at the upper end of
these ranges can be achieved by modifying the boom configura-
tion to avoid having the point of maximum boom sag coincide
with the region of maximum flow velocity, and by designing the
boom unit cross-sectional geometry to optimize ice capture effi-
ciency. In deeper rivers, the velocity criterion is more important,
since the greater depth would allow the Froude number criterion
to be met at an unrealistically high velocity. Froude numbers and
surface water velocities for a number of successful ice boom
applications are provided in Table 1. Ice may override a boom
where wind is the main driving force, even though the velocity
and the Froude number are well within the acceptable ranges.
Under marginal conditions, ice cover formation behind a boom
may require some form of hydraulic control, such as a down-
stream dam or weir, to raise the water level and reduce surface
water velocity. As mentioned earlier, if flow control is available,
favorable hydraulic conditions may be achieved through flow
reduction during the critical ice formation period.
Design loads
The most important forces acting on an ice boom typically
result from water shear on the underside of the ice cover and wind
stress on the ice cover surface. Additional forces to consider
include the downslope component of the gravity force on the ice
accumulation, water drag on the upstream face of the ice cover or
the boom unit itself, ice impact forces, and forces caused by
vessel passage. The total force on an ice boom (fb), per unit width
of river, can be expressed as the sum of all forces:
fb = fw + fa + fg + fd + fi + fv
(1)
where fw = water shear on the underside of the ice accumula-
tion
fa = wind drag force on the ice cover
fg = downslope component of the gravity force on the
ice accumulation
fd = water drag on boom unit or the upstream face of the
ice cover
fi = force resulting from ice impacting the boom
fv = forces resulting from vessel passage.
One of the most difficult aspects in ice boom design is estimat-
ing the length or area of the ice cover that contributes to the ice
load on the boom. In rivers, ice loads acting on a boom are often
assumed to derive from an area that extends three to five river
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