Effects of Ice Boom Geometry on Ice Capture Efficiency
GORDON GOOCH
Model tests using synthetic plastic beads can
INTRODUCTION
compare the ice retention capabilities of ice booms
An ice boom is a series of floating timbers joined
under controlled laboratory conditions. Model and
together with a cable and anchored to shore or
prototype ice boom behaviors are compared in this
riverbed anchors. The purpose of an ice boom may
report to emphasize the similarities between field
be to divert floating ice away from problem areas
and laboratory results.
or to collect it to encourage the formation of a solid
ice sheet on a river. The sheet will insulate the
water beneath, eliminating ice production in those
BACKGROUND
locations. A reduction in ice volume can signifi-
Site assessment criteria for ice cover formation
cantly reduce water levels and prevent ice jam
The criteria for a properly designed and func-
flooding. Researchers have been testing low-cost
tioning ice boom include many of the same gener-
solutions to encourage ice sheet formation on
al principles as debris booms (Perham 1987, 1988).
small, fast-moving, frazil-producing streams using
Froude number, flow velocity, ice forces and site
ice booms. Frazil ice has been found to be the lead-
layout must all be within acceptable limits. The
ing cause of ice jam flooding. Frazil ice begins as
Froude number is the ratio of the velocity divided
small ice particles and quickly forms into larger
by the square root of gravity times the flow depth.
ice pans, which can restrict the flow capacity of
It is very useful, along with pool length, in deter-
rivers and streams.
mining if a location will meet minimum require-
In this report, laboratory and field tests of ice
ments for an ice control structure (ICS). Based on
boom geometries are discussed, along with their
flow depth, an upper Froude number limit of 0.10
ability to capture floating ice and form a solid ice
is commonly used in selecting a site. The river pool
cover. How well this can be done is referred to as
length in open-water conditions should be greater
the "ice capture efficiency." In laboratory tests the
than two river widths (Table 1). Experience has
ice capture efficiency is dramatically improved
shown that without these two minimum require-
when the incoming ice is first directed to the shore,
ments, a conventional ice formation boom may not
where it becomes stationary and thickens.
Table 1. River hydraulics at ICS sites.
Oil Creek boom
Oil Creek weir
Allegheny R. boom
Salmon River boom
(198182) (198283)
(1988)
(198283)
(198991)
Average depth
(ft)
2
2.80
5
4.2
3
(m)
0.60
0.85
1.52
1.28
0.91
Flow velocity
(ft/s)
1.4
1.2
0.5
0.94
2.0
(m/s)
0.42
0.36
0.15
0.28
0.6
Froude number
0.17
0.13
0.04
0.08
0.21
Discharge
(cfs)
538
460
900
1870
900
(cms)
15
3
25
52
25
Channel width
(ft)
190
151
351
540
230
(m)
57
46
106
164
70
Pool length
(ft)
323
250
2431
600900
1478
(m)
98
76
740
182274
450
Length/width ratio
1.7
1.6
6.9
1.6
6.4
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