SHEET ICE RETENTION STRUCTURES
structures, and Ashton (1986) contains a brief ver-
sion of Perham's review. At the same time, struc-
Sheet ice retention structures promote ice for-
tural ice control techniques were evolving in
mation on water bodies with relatively low sur-
northern Europe, the main focus being on hydro-
face velocities (≤ 2.3 ft/s), low energy slopes and
power. Roen and Tesaker (1988) discussed a
low Froude numbers (≤ 0.08) (Perham 1983). Hy-
range of ice problems and structural solutions at
draulic conditions must allow for arriving ice to
hydroelectric plants in Norway, presenting five
accumulate against the structure (juxtapose),
case studies. At a more general level, Carstens
rather than be dragged beneath the surface dur-
and Tesaker (1987) presented a general inventory
ing the formation period. The cover typically
of ice problems on rivers, listing possible struc-
progresses from the structure in the upstream or
tural solutions. Calkins (1984) presented six case
windward direction, and arriving ice may be in
studies of ice jam problems on rivers in the U.S.
the form of frazil, floes or brash. The main goal
and Canada, in outline form, briefly describing
of a sheet ice retention structure is to initiate ice
existing and proposed structural solutions.
cover formation. Once a solid cover has formed,
A project headed by Harold Belore of the con-
the structure is usually not designed to add to
sulting firm CummingCockburn and Associates,
the cover's overall stability. Although sheet ice
Ltd. (1986a) produced a comprehensive overview
retention structures are typically not designed to
of ice control methods on small rivers in Canada
retain breakup ice, they may make breakup less
where dams, weirs, piers and booms were used
severe by delaying the breakup of the upstream
successfully to mitigate both freeze-up and break-
ice cover until the downstream ice has had a
up ice problems. Belore et al. (1990) also de-
chance to clear out.
scribed a variety of structural methods, ranging
from sheet ice control structures on the St. Law-
Purposes
rence River to weir-and-pier structures designed
Retention or stabilization of a sheet ice cover
to control breakup ice on smaller Canadian
has a number of positive effects. Stabilizing the
rivers. Deck (1984) briefly presented a structural
shore ice on a river or lake reduces the ice vol-
solution to the ice jam problems at Oil City in
ume supplying potential ice jams at locations
Pennsylvania. Deck and colleagues later drew on
downstream. As an added benefit, a stable shore
the Canadian experience with weir-and-pier
ice zone protects the shoreline and shoreline
structures to develop a design for a proposed ice
structures from the destructive effects of off-
control structure on Cazenovia Creek near Buffa-
shore ice movement. In cases of winter naviga-
lo, New York (Gooch and Deck 1990).
tion, stabilization of the ice along the channel
Jain et al. (1993) contains a summary of ice con-
sides minimizes the ice volume in the navigation
trol methods, describing the point at which a
channel and increases the channel's ice-flushing
nonstructural solution such as flow control may
capacity. At lake-to-river transition areas, special
become more feasible than a structural one on the
booms, some with navigation openings, have
larger rivers in the U.S. The innovative methods
been developed to prevent lake ice from enter-
of controlling pack ice off the northern coast of Ja-
ing and clogging the narrower downstream
pan described by Saeki (1992) are mentioned in
channels.
this report since they could possibly be applied to
Formation booms may be placed on a river or
ice problems at the confluences of large rivers in
canal to stop the downstream transport of frazil
the U.S.
ice and promote the upstream progression of an
So why write this review? At the very least,
ice cover. The hydropower industry in northern
this effort is of value since it assembles much of
climates has used this type of boom extensively
the relevant information in one place. In addition,
to promote the rapid formation of an ice cover
this report is more complete, taking a broader
upstream of their intakes early in the ice season,
perspective than much of the general literature. A
minimizing ice-related head losses and increas-
single information source may help eliminate the
ing winter power production. Though not spe-
need to rediscover previously used methods.
cifically designed for the purpose, these booms,
Other than the focus on structural ice control
alone or in series, may help prevent ice floes
methods that could be applied to river confluenc-
from piling up and damaging hydropower in-
es, this review is not limited to any particular size
takes at breakup. In addition to increasing the
or type of river or structure nor is it constrained
reliability of winter hydro production, formation
to any specific geographical region.
booms have effectively reduced the ice jam
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