gram. The review brings together information
formation of a stable, floating ice accumulation,
on a wide range of ice control structures, assess-
with relief flow passing underneath the ice and
ing their performance. General conclusions are
over the weir crest. Properly designed, weirs
presented on the current state of development in
and dams retain breakup ice runs with great re-
the field of structural ice control. The next sec-
liability. As an added benefit, dams may serve
tion examines how well existing methods (as
as freeze-up ice control structures by promoting
well as relatively untried ones) apply to a range
ice cover formation early in the season, thereby
of confluence ice situations. Finally, a range of
reducing frazil production. Major drawbacks are
existing ice control structures will be examined
their high capital cost, the obstacles presented to
with respect to channel depth and average vel-
navigation and fish migration, and upstream
ocity.
sedimentation. An example of a successful ice
control weir is the structure on the Ste. Anne
River in St. Raymond, Quebec. As a further
General conclusions
Structural methods to help form and retain
drawback, permitting for new dam construction
sheet ice are well developed and relatively well
at present is difficult in the U.S. There may be
understood. Floating booms, the most common
some potential for ice control using inflatable
structure type in this group, do not significantly
dams, however.
alter the existing hydraulic conditions, and their
The greatest development potential in the
environmental impact is minimal. Their initial
field of breakup ice control lies in pier struc-
capital cost is low, and applications are possible
tures. A grounded jam forming behind the piers
in very deep channels. A floating boom solution
creates an impoundment, allowing the forma-
applies to a relatively narrow range of hydraulic
tion of a stable floating ice accumulation up-
conditions, however, and reliability can be limit-
stream. Relief flow is typically routed around
ed, as seen in the ice runs that override the Lake
the grounded portion of the jam via some type
Erie boom. The selection of ice boom design to
of channel in the overbank area. In the non-ice-
date has been based on a combination of theory,
jam case, these structures do not cause a rise in
experience, physical model studies and avail-
water level, so they do not create a barrier to mi-
ability and cost of construction materials. The re-
grating fish or cause upstream sedimentation.
lationship between a boom unit's cross-sectional
Their capital cost is lower than for an equivalent
geometry and its capture efficiency is not that
weir structure. Being relatively new technology,
well understood, however. Recent applications
the ice and hydraulic design aspects are tricky
of note are the formation booms installed on the
and not that well understood, so their reliability
Salmon River in Idaho and the Allegheny River
may be less than for a weir. Scour and debris
at Oil City, Pennsylvania. In both cases the
clogging are also potential problems. A success-
booms caused ice covers to form at locations
ful example is the pier structure built on the
where the hydraulic conditions were previously
Credit River at Mississauga, Ontario. Future
thought to be unfavorable. The future may see
directions might be to scale the current small
reduced installation and removal costs through
river applications up to larger rivers or to devel-
the further development of sink-and-float
op removable frames or collapsible piers that do
booms. Efforts are now underway to increase ice
not interfere with navigation. Application of
boom capture efficiency. These designs might
pier ice control structures to moveable-bed riv-
lead to successful ice retention at surface veloci-
ers also presents a major challenge.
ties well above the currently accepted maximum
Recent innovations in freeze-up ice control in-
of 2.3 ft/s. Finally, floating boom technology
clude the development of fence booms, tension
might be further developed for the purpose of
weirs and ice nets. Though limited in their range
breakup ice control.
of application, these methods are extremely in-
Compared to sheet ice retention, breakup ice
expensive and easy to deploy. An example of a
control methods are less developed and less well
recent success is the ice fence located upstream
understood. Dams and fixed weirs are effective
of a small hydro station on the island of Hok-
and time-tested breakup ice control methods,
kaido in Japan. Ice nets caused the formation of
and the icehydraulic design aspects involved
an ice cover upstream of the Stornorrfors power
are fairly straightforward. The object is to create
station on the Ume river in Sweden, with sur-
upstream hydraulic conditions of sufficiently
face velocities in the 3-ft/s range, well above the
low slope and low surface velocity to allow the
accepted maximum for booms of 2.3 ft/s. The
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