shear booms are not without potential. Perhaps
ice nets have the additional advantage of no
floating ice could be diverted towards the shore
depth limitation. Perhaps the nets could be used
or onto floodplains for storage, or directed away
upstream of booms in borderline formation situ-
from navigation channels and fleeting areas on
ations. Some adaptation of the ice net could pos-
large rivers. Weirs and dams get high rankings
sibly be used to stabilize and retain shore ice at
in nearly all categories when dealing with both
locations downstream of peaking hydro dams as
breakup and freeze-up ice problems. Finally,
well.
piers apply potentially to many confluence ice
control situations, although, to date, they have
Applicability of structural ice control methods
been tested only on small to medium-sized
to river confluence situations
rivers.
A future phase of the work unit on structural
ice control will evaluate various structural solu-
tions at selected confluences. This section serves
Channel depth and water current velocity
as a lead in, indicating which methods have
at selected structures
As a final overview, the closing section of this
potential in which applications. Table 1 ranks
report examines the range of existing structures
the applicability of selected structural ice control
with respect to river depth and velocity (Fig. 27,
methods to five confluence situations. For the
Table 2). The structures are divided into six
sake of simplicity, only the five major structure
groups according to type and function:
categories are considered:
Formation booms;
Floating booms;
Formation weirs;
Shear booms;
Tension weirs;
Man-made islands;
Lines and nets;
Weirs and dams; and
Pier breakup structures; and
Piers and boulders.
Weir and pier combinations.
The structure types are grouped according to
For methods that significantly raise the water
function, i.e., freeze-up and breakup. They are
level, such as weirs and piers, velocities and
further categorized as removable or fixed.
Table 1. Applicability of structural ice control methods to river confluence situations.
Breakup
Freeze-up
Fixed
Removable
Confluence
Floating Shear Man-made Weirs and Piers and
situation
Example
booms booms
islands
dams
boulders
Large riverLarge river
MississippiMissouri
3*
3*
3*
5
4*
Small riverLarge river
Oil CreekAllegheny R.
5
1*
0
5
5*
Large lakeLarge river
Lake ErieUpper Niagara R.
5
1*
4
0
4*
Large riverLarge lake
St. Lawrence R.Lake St. Peter
5
1*
5
4
3*
Small riverLake
Czech RiversReservoirs
0
0
0
4
5
* Indicates potential application, but not tried.
Scale:
0123
4
5
not
highly
applicable
applicable
depths are given for the pool immediately up-
Floating booms, man-made islands, and weirs
stream of the structure. The groups fall into
and dams apply well to relatively low velocity
somewhat distinct fields, as shown in Figure 27.
confluence situations where a stable ice cover is
Formation booms, the most common type of ice
desired. Careful location of formation booms
control structure, have the greatest range of ap-
upstream of large riverlarge river confluences
plication, particularly in terms of depth. For for-
may reduce the ice supply to the main stem and
mation booms the maximum possible velocity is
the severity of resulting ice jam problems.
approximately 2.5 ft/s. The depth ranges from
Although never tried in confluence situations,
22
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