floated automatically by the injection of com-
and promote ice cover formation (Perham 1983,
pressed air. Developed by Nishimura-Gumi Co.
U.S. Army Corps of Engineers 1985). Updated
LTD, the pontoons have a teardrop cross-
information on the performance of these struc-
sectional shape, minimizing the tendency for
tures is not available. Burgi modeled opposing
burial by deposition of sediment while resting
groins as a means of enhancing boom perfor-
on the bed.
mance on the North Platte, upstream of Casper,
Wyoming (Burgi 1971). The groins were not
Groins
built, however.
With the exception of artificial islands, the
Submerged weirs are being constructed along
Montreal Harbor ICS and the Japanese sink-and-
the outside of bends on the Mississippi to direct
float booms, all structures described up to this
flow towards the dredged navigation channel.
point have been floating, flexible, seasonally de-
These structures, known as bendway weirs, are
ployed and relatively inexpensive. None of the
mentioned in this report since they are likely to
structures described so far cause a significant
improve ice conveyance. Engineers in the St.
water level change in the absence of ice or act as
Louis District of the U.S. Army Corps of Engi-
a barrier to migrating fish. Aside from midchan-
neers would like to locate a series of bendway
nel anchors for multiple-span booms, ice booms
weirs at the MississippiMissouri River conflu-
have little negative effect on the riverbed. Much
ence (Civil Engineering 1994). If constructed, the
of this is in contrast to the next group of fixed-
effect of this channel modification on the local
sheet ice retention structures, which includes
ice regime will be observed closely since this lo-
groins, weirs and dams.
cation is a well-known ice jam problem site.
As mentioned earlier, the majority of sheet ice
Bendway weirs may prove to be an effective ice
retention methods are successful only under the
control tool in the future.
hydraulic conditions of relatively low energy
slope, low water surface velocity and low
Dams and fixed weirs
Froude number. By raising the upstream water
Although seldom constructed solely for ice
level, groins, weirs and dams may create condi-
control, the most effective ice control structure is
tions favorable for the formation of a sheet ice
a dam or weir. By raising the water level and re-
cover. In addition, structurally raising the water
ducing the water current velocity, these struc-
level and reducing the surface water velocity
tures may allow the thermal growth of an ice
may make the capture of ice behind a boom pos-
sheet or serve as a barrier for the juxtaposition of
sible where it was not before.
frazil or frazil pans. The pool behind a dam or
Stone groins, or jetties, extending perpendicu-
weir stores frazil transported from open reaches
larly into the channel from the shoreline, stabil-
above, preventing its transport to a potential
ize the shore ice and may, under the appropriate
freeze-up jam site below. A later section of this
hydraulic conditions, encourage bridging and
report describes how weirs with piers reduce the
ice cover formation across the channel. The tops
severity of breakup ice jams by retaining a stable
of these structures are typically above the water
ice accumulation, thus limiting the ice supply to
level during the freeze-up period. As an added
potential downstream jams.
benefit, the groins raise the upstream water
Sartigan Dam, upstream of St. Georges, Que-
level, creating hydraulic conditions more favor-
bec, with a drop of 40 ft, creates a 2.5-mile-long
able for ice cover formation, with or without the
pool on the Chaudiere River (Fig. 10). The dam
use of ice booms. Groins, since they do not cross
was designed and built in 1967 for the sole pur-
the entire channel width, have an environmental
pose of ice control (Michel 1971). Much of the
advantage over weirs and dams since they do
frazil that once contributed to the severe jams at
not totally obstruct navigation or migrating fish.
St. Georges is now stored beneath the pool's ice
A system of groins, used in conjunction with
cover. Small stone weirs, some experimental,
booms, promotes ice cover formation upstream
have been used to form pools and trap frazil on
of the hydrostation at Hestefoss in northern
other rivers in Quebec, Ontario and northern
Norway (Kanavin 1970, Perham 1983, U.S. Army
New England (Perham 1983, U.S. Army Corps
Corps of Engineers 1985). On the Burntwood
of Engineers 1985, CummingCockburn and
River of the Churchill River Diversion Project,
Associates Ltd. 1986a).
Manitoba Hydro uses two opposing groins, or
A 6-ft-high, concrete-capped, rock-filled gabion
wing dikes, to raise the upstream water level
weir with sluiceway slots on the Israel River has
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