The Allegheny boom, an innovative upstream vee
Formation booms to prevent ice jam flooding
[V] design, pushes flow and ice towards the
along rivers
shores, to capture frazil and form a cover at a
Formation booms have helped solve ice jam
location where a traditional single-sag boom had
problems on poolriffle rivers. Freeze-up jams
failed. The tip of the vee was connected by cables
occur naturally at slope reduction points, pro-
to anchors on each bank, eliminating the need for
gressing upstream, sometimes flooding towns
a midchannel anchor. Since the hydraulic condi-
and property. Thick frazil deposits may also in-
tions at the site are marginal, successful ice cover
crease the ice volume supplying potential break-
growth behind the boom depends on flow reduc-
up jams, or if the deposits remain in place at
tion at an upstream dam during the formation pe-
breakup, the frazil may stop ice floes from
riod. This boom, in conjunction with a weir struc-
upstream, resulting in a breakup jam. A forma-
ture to trap frazil on Oil Creek, has significantly
tion boom may be installed to create an ice cover
reduced the occurrence of breakup ice jam flood-
upstream of the traditional problem area. The
ing in Oil City since its first installation in 1982
ice cover behind the boom reduces local frazil
(Perham 1983, Deck and Gooch 1984, U.S. Army
production and captures much of the frazil
Corps of Engineers 1985, Gooch and Daly, in
arriving from upstream.
prep.).
This was the design intent of the timber boom
A pair of 200-ft-wide ice booms was installed
installed in 1989 on the Salmon River upstream
in 1968 on the North Platte River, seven miles
of Salmon, Idaho, a town that had historically
upstream of Casper, Wyoming, to protect a resi-
experienced a freeze-up ice jam flood one out of
dential development from freeze-up ice jam
every three years. During the Salmon boom's
flooding. A physical model study by Burgi (1971),
second year of use, in 1990-91, the right bank
of the Bureau of Reclamation, found an upstream
anchor was relocated 240 ft upstream as shown
vee design optimal, similar to the configuration
in Figure 8. The new configuration diverted sur-
used over a decade later on the Allegheny River
face flow and ice away from the zone of highest
boom at Oil City. However, on the North Platte a
surface velocity, greatly improving the frazil
single-sag design, rather than the upstream vee,
capture efficiency. Although difficult to quantify
was used, perhaps due to the added complication
because of the short period of record, the Sal-
of placing midchannel anchors in a moveable-bed
mon boom appeared to have a positive effect in
river. The design was also unique in that the 14-
terms of limiting the progression of potential
in. 20-in. 12-ft timbers had steel spikes pro-
freeze-up ice jams below the town of Salmon
truding 6 in. above and below, in an attempt to
during the winters of 1989-1992. The boom was
increase frazil capture efficiency. It appears that
not installed for the 1992-93 or 1993-94 winters,
the booms are no longer installed, however, since
however (Axelson et al. 1990, White 1992, White
Bureau of Reclamation personnel near Casper
and Zufelt 1993).
know nothing about them.*
A well-sited formation boom on the Alle-
gheny River (Fig. 9) significantly reduced the
Sink-and-float ice booms
volume of frazil depositing every winter at the
Since the annual installation and removal of
mouth of Oil Creek near Oil City, Pennsylvania.
ice booms is costly, the Canadian Coast Guard is
considering the use of a sink-and-float boom (yet
to be developed) on Lake St. Peter. At the end of
the ice season the booms would simply be sunk
in place for storage during the open-water sea-
son. During the late fall the individual pontoons
would be raised to the surface, drained and re-
floated. An existing structure, similar in concept,
protects the harbor entrance at Hokkaido, Japan,
from drifting pack ice (Imaizumi et al. 1993).
When there is no pack ice present, or during win-
ter vessel transits in and out of the harbor, the
pontoons lie on the seabed. The pontoons are re-
Figure 9. Allegheny River ice boom.
* Personal communication with Phil Burgi, 1994.
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