threat to towns and properties along rivers by
capturing frazil at favorable locations upstream
of the historic ice jam sites.
Types
A wide variety of sheet ice retention struc-
tures exist, many of which are well described
and illustrated by Perham (1983) and Appendix
B of the Ice Engineering Manual (U.S. Army
Corps of Engineers 1985). The list includes con-
ventional floating booms, rigid booms, weirs,
groins and artificial ice islands. Many struc-
tures such as dams, bridge piers and tower
foundations, although not specifically designed
a. Ice island along the northern edge of the navigation
to control ice, do serve that purpose. In addi-
channel to stabilize shore ice.
tion, piers, piles and pile clusters (dolphins)
and, in some cases, sunken vessels have been
used to stabilize a sheet ice cover.
Examples
Examples are presented in six groups, ac-
cording the general type of structure and the
purpose of the ice control. The first group cov-
ers sheet ice control methods used on large riv-
ers with winter-long navigation. In the second
group, examples of ice control at channel con-
strictions and lakeriver confluences are pre-
sented. Ice booms and winter hydropower is
the topic of the third group. The fourth group
deals with formation booms to prevent ice jam
flooding along rivers. Sink-and-float booms are
the topic of the fifth group. Examples of sheet
ice retention using weirs, groins and dams form
Figure 1. Ice island on Lake St. Peter.
the final group.
Ice control on rivers and waterways with
winter-long navigation
ure 1 shows an ice island on Lake St. Peter re-
On the lower St. Lawrence River, where win-
taining sheet ice during the early spring. Perham
ter-long navigation extends as far upstream as
(1983), Appendix B of the Ice Engineering Man-
Montreal, the ice management program de-
ual (U.S. Army Corps of Engineers 1985) and
pends in part on structural methods to retain
Lawrie (1972) provided more detailed informa-
and stabilize sheet ice. Here the ice control ef-
tion. The five islands on the south side of the
fort has the goals of preventing the ice jams that
navigation channel were constructed after 1985.
have historically flooded Montreal and of en-
Initial construction and maintenance of the ice
suring safe and efficient navigation to the port
islands are costly. The islands must periodically
of Montreal. At Lake St. Peter, 45 miles down-
be topped off to compensate for continual settle-
stream from Montreal, the St. Lawrence River
ment in the soft lake sediments. Upstream of
widens and flattens, significantly reducing the
Montreal, three similar islands in Lake St. Louis
river's ice conveyance capacity. Here, nine arti-
prevent floes from entering the navigation chan-
ficial islands effectively stabilize the ice be-
nel during the early part of the navigation sea-
tween the shore and the centrally located,
son (Perham 1983).
dredged navigation channel. These islands,
The four booms in the northeast corner of
constructed of quarried rock, have base diame-
Lake St. Peter, depicted in Appendix B of the Ice
ters of 130 ft and are spaced 2500 ft apart. Fig-
Engineering Manual (U.S. Army Corps of Engi-
3
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