Cold Regions Technical Digest

No. 96-1, April 1996

Design of Ice Booms

Edward P. Foltyn and Andrew M. Tuthill

US Army Corps

of Engineers

Cold Regions Research &

Engineering Laboratory
CRREL’s Cold Regions Technical Digests are

aimed at communicating essential technical

information in condensed form to researchers,

engineers, technicians, public officials and others. They convey up-to-date knowledge concerning technical problems unique to cold regions. Attention is paid to the degree of detail

necessary to meet the needs of the intended

audience. References to background information are included for the specialist.
This technical digest provides basic engineering design guidance for floating ice retention structures or ice booms. Basic types

of booms and their ice control objectives are described briefly. The

basic theory and equations used in ice boom design are then presented and typical structural components described. The report

addresses other design considerations, such as boom layout, geometry, and anchor systems, as well as the selection of wire rope and

connection systems, and concludes with an example ice boom

design at a specific site. This technical digest not only incorporates

and builds on ice boom design information found in EM 1110-2-

1612, Ice Engineering (U.S. Army Corps of Engineers 1982), but

describes the actual design steps in greater detail, and elaborates

on boom geometry and the forces acting on ice boom components.

Booms are flexible wire rope structures designed to control

floating ice or debris. Ice booms are installed each winter by

hydroelectric and navigation interests to promote rapid ice cover

formation by retaining frazil and floating sheet ice. They are also

used to prevent brash ice and floes from interfering with hydroelectric intakes and navigation channels. An ice boom typically

consists of a series of floating structural members or boom units,

attached to a main boom cable. Figure 1 shows a typical ice boom

arrangement. An ice boom’s ability to deform and submerge will,

in most cases, prevent its failure under extreme loading. Ice retention by conventional ice booms is limited to hydraulic conditions

COLD REGIONS TECHNICAL DIGEST No. 96-1, April 1996

USA Cold Regions Research and Engineering Laboratory

Hanover, New Hampshire 03755-1290

Design of Ice Booms

Edward P. Foltyn and Andrew M. Tuthill

Introduction

The authors are

a private consultant

and a research

hydraulic engineer

 in CRREL’s Ice

Engineering Research

Division, respectively.

Types of ice

booms and

 their uses
 COLD REGIONS TECHNICAL DIGEST NO. 96-1

of mild slope and relatively low surface water velocity. Booms are

typically not designed to retain breakup ice runs.

Ice booms having the main purpose of frazil ice retention, both

to enhance winter hydropower production and to reduce the potential for ice jam flooding during freezeup, are sometimes termed

“formation booms.” This type of boom is also used to form and

stabilize shore ice adjacent to navigation channels and to alleviate

frazil problems associated with winter navigation at the approaches

to locks and dams. Other types of booms are designed to retain or

divert brash or floes, and apply to ice problems associated with

winter navigation, the operation of locks and dams, and winter

hydropower production.

By retaining frazil ice, formation booms promote rapid ice

cover growth during the early ice season. The ice cover that forms

behind a boom insulates the water beneath, eliminating local

frazil ice production. At the same time, the cover traps frazil

arriving from upstream, preventing its transport to traditional ice

problem sites downstream. Formation booms, often placed in

series, have been used successfully for many decades to alleviate

frazil ice problems associated with hydroelectric production. During the early ice season, these booms promote the rapid growth of

a smooth sheet ice cover upstream of hydropower intakes, minimizing the head losses that commonly result from frazil accumulations and the formation of hanging dams. Where flow control is

an option, discharge reductions during the critical ice formation

period may accelerate the rate of ice cover growth and reduce

1. Typical ice boom

arrangement. In this

case, boom units are

constructed of doubled

1- × 1- × 12-ft (0.3-

0.3- × 3.7-m) timbers,

connected by chain to

the boom cables. The

boom cables connect to

the anchor cable via a

junction plate, supported by floats.

2
DESIGN OF ICE BOOMS

force levels on the booms. Once a solid ice cover has formed,

most of the downstream forces on the ice cover are transferred to

the channel banks rather than to the boom, and the flow can be

increased to pre-freezeup levels.

Formation booms are also used to reduce the threat of ice jam

flooding on pool–riffle river reaches by capturing and retaining

frazil at locations upstream of the problem area, thus preventing

the formation of freezeup jams farther downstream. By decreasing the volume of frazil accumulations in problem reaches, the

booms may also alleviate ice jam flooding by reducing the prebreakup ice volume.

In addition to promoting ice formation, booms are used to

control ice accumulations made up of floes or brash. Booms have

been used successfully at channel constrictions, both to promote

arching and to prevent brash ice from blocking the narrower

downstream channels. Figure 2 is an example of a boom with a

navigation opening, designed to prevent wind-driven lake ice from

entering a hydropower canal. Booms may be designed to divert

frazil or brash ice away from lock entrances or hydropower intakes. In some applications a boom may have the dual purpose of

retaining frazil early in the ice season and controlling brash ice as

the ice cover begins to deteriorate.

Additional information on successful ice boom designs may be

found in EM 1110-2-1612 Ice Engineering (U.S. Army Corps of

Engineers 1982) and CRREL Report 83-30, Ice Sheet Retention

Structures (Perham 1983). CRREL Special Report 95-18, Struc2. Ice boom with a

navigation opening,

designed to prevent

wind-driven lake ice

from entering a

hydropower canal on

the St. Lawrence

Seaway.

3
 COLD REGIONS TECHNICAL DIGEST NO. 96-1

tural Ice Control; Review of Existing Methods (Tuthill 1995)

updates Perham (1983). CRREL Special Report 92-21, Salmon

River Experimental Ice Boom (White 1992) provides background

information on ice boom design, focusing on formation booms on

pool-riffle rivers.

Ice booms have many advantages over fixed ice control structures such as weirs, piers, piles, and man-made islands. Booms

are generally installed in the fall, just before the onset of the ice

formation season, and removed in the spring, shortly after ice-out.

They therefore do not interfere with open water uses of the river

or lake, such as recreation and commercial navigation. Booms

have a negligible effect on the natural hydraulic conditions of the

river, causing only minor changes in water depth and current

velocity. They typically do not cause scour or the deposition of

sediment, nor do they present a barrier to migrating fish. In addition, floating structures avoid the foundation settlement problems

typical of fixed structures in rivers and lakes with soft clayey

bottom sediments. Ice booms are designed to submerge under

extreme loading conditions, avoiding structural failure. This feature allows the structures to survive breakup and impacts from

large floes. Ice booms may be assembled from a wide variety of

commonly available materials and components, reducing costs

and construction time, and booms are readily installed using standard maritime or land-based construction equipment.

One possible limitation of ice booms is that, although the initial cost of an ice boom is low relative to a fixed ice control

structure, the ongoing costs of installation, removal, and maintenance may be substantial.

The main hydraulic constraint to floating ice retention structures is that they are effective only at sites with mild slope and

associated low surface water velocity. Surface water velocity and

depth are important, since they strongly affect the total ice force

acting on the boom. Wind stress on the ice cover is also important.

If the water drag and wind stress on the ice are too great, the ice

pieces may underturn and pass under the boom, or the ice may

ride up and submerge the boom unit to pass over the top. A great

deal of research and practical experience gives a range of 0.08 to

0.12 for the maximum Froude number,* and 2–2.5 ft/s (0.6–1.4

* Froude number: F V gh R = , where V = average channel velocity upstream of

the ice cover, h = average channel depth upstream of the ice cover, and g =

acceleration of gravity.

Hydraulic

constraints

Advantages and

limitations of

ice booms

4
DESIGN OF ICE BOOMS

m/s) for the maximum velocity. Ice retention at the upper end of

these ranges can be achieved by modifying the boom configuration to avoid having the point of maximum boom sag coincide

with the region of maximum flow velocity, and by designing the

boom unit cross-sectional geometry to optimize ice capture efficiency. In deeper rivers, the velocity criterion is more important,

since the greater depth would allow the Froude number criterion

to be met at an unrealistically high velocity. Froude numbers and

surface water velocities for a number of successful ice boom

applications are provided in Table 1. Ice may override a boom

where wind is the main driving force, even though the velocity

and the Froude number are well within the acceptable ranges.

Under marginal conditions, ice cover formation behind a boom

may require some form of hydraulic control, such as a downstream dam or weir, to raise the water level and reduce surface

water velocity. As mentioned earlier, if flow control is available,

favorable hydraulic conditions may be achieved through flow

reduction during the critical ice formation period.

The most important forces acting on an ice boom typically

result from water shear on the underside of the ice cover and wind

stress on the ice cover surface. Additional forces to consider

include the downslope component of the gravity force on the ice

accumulation, water drag on the upstream face of the ice cover or

the boom unit itself, ice impact forces, and forces caused by

vessel passage. The total force on an ice boom (fb), per unit width

of river, can be expressed as the sum of all forces:

f f f f f ff b wag = + + + ++ d i v (1)

where fw = water shear on the underside of the ice accumulation

fa = wind drag force on the ice cover

fg = downslope component of the gravity force on the

ice accumulation

fd = water drag on boom unit or the upstream face of the

ice cover

fi = force resulting from ice impacting the boom

fv = forces resulting from vessel passage.

One of the most difficult aspects in ice boom design is estimating the length or area of the ice cover that contributes to the ice

load on the boom. In rivers, ice loads acting on a boom are often

assumed to derive from an area that extends three to five river

Design loads

5
 COLD REGIONS TECHNICAL DIGEST NO. 96-1

widths upstream from the structure (U.S. Army Corps of Engineers 1982). In other words, beyond three to five river widths

upstream of the boom, forces on the ice cover are transferred

laterally to the banks rather than to the boom. This assumption is

greatly influenced by the ice cover type and the degree to which

the ice is attached to the shore. A full explanation is beyond the

scope of this report, but important factors are the ice piece size,

ice cover thickness, and the river width, as well as the cohesion

and the angle of internal friction of the ice accumulation. During

the initial formation period, the greatest forces typically occur

when the ice cover is the least consolidated. Peak force levels

may also occur just before breakup, as the ice cover begins to

fracture and detach from the shores. Once the ice pieces freeze to

each other and to the banks, the force on the boom can fall off

Table 1. Information on successful ice boom designs.

Geometry

Structure size

 Location type Function* Material ft (m)

St. Lawrence River Single icfs, p Douglas fir Rectangular

International Section timber fr, br 1.2 × 1.8 × 30

(0.4 × 0.5 × 9)

Lake Erie, Buffalo, Single icfs, p Douglas fir Rectangular

New York timber fr, br, fl 1.2 × 1.8 × 30

(0.4 × 0.5 × 9)

Lake Erie, Buffalo, Single icfs, p Steel Circular

New York pipe fr, br, fl 2.6 × 30

(0.76 × 9.1)

Lake St. Peter, Single icfs, p Douglas fir Rectangular

St. Lawrence River timber 1.2 × 1.8 × 30 ft

(0.4 × 0.5 × 9)

St. Marys River, Single n Douglas fir Rectangular

Sault Ste. Marie, Michigan timber brash 1.0 × 2.0 × 20

(0.3 × 0.6 × 6)

Lake St. Peter, Single icfs, n Steel pipe Circular

St. Lawrence River pontoon 2.0 diam. × 30

(0.6 diam. × 9)

Allegheny River, Single icfs, ijr Steel, Rectangular

Oil City, Pennsylvania pontoon foam filled 1.3 × 2.7 × 20

(0.4 × 0.8 × 6)

Beauharnois Canal, Double icfs, n, p Hollow Parallel,

St. Lawrence River pontoon steel 3 diam. × 20

6 on center

(0.9 diam. × 6

1.8 on center)

Salmon River, Idaho Triple icfs Douglas fir 1 × 1 × 20

timber (0.3 × 0.3 × 6)

*icfs = ice cover formation and stabilization

ijr = ice jam reduction

p = hydroelectric power

n = navigation

6
DESIGN OF ICE BOOMS

Force per unit width Average Average water

Span (kip/ft)† (kN/m) depth velocity Froude

ft (m) Designed Measured ft (m) ft/sec (m/s) number

400 0.58 17–29 0.95–2.75 0.02–0.12

(122) (8.5) (5–9) (0.29–0.84)

400 1.38 0.37 18 1.5 0.06**

(122) (20.1) (5.4) (5.5) (0.46)

400 0.62 0.97 18 1.5 0.06**

(122) (9.1) (14.1) (5.5) (0.46)

400 0.64 100 1 0.06

(122) (9.3) (31) (0.3)

205 0.73 10–31 2.7 0.09–0.15

(63) (10.7) (3–9) (0.82)

avg.

400 0.25†† 10 1 0.06

(122) (3.7) (3) (0.3)

250 1.12 5.4 1.15 0.09

(76) (16.3) (1.7) (0.35)

118 3.2 34 2.4 0.07

(36) (47) (10) (0.73)

260 0.66 0.42 5 2.5–3 0.16–0.012

(79) (2.2) (6.1) (1.5) (0.76–0.9)

†kips = kilopounds of force

**Wind driven lake ice can override boom

††Estimated force level at time of anchor cable failure

dramatically. For booms at lake-to-river confluences, where ice

arch formation tends to occur naturally, the forces on the boom

have been assumed to derive from a 45°–45°–90° triangular area

of ice upstream of the boom, the long side of the triangle aligned

with the length of the boom (Abdelnour et al. 1994). Figure 3

shows the fractured ice area that contributes to the ice loading for

a wide boom on a lake. Note that the maximum load occurs at the

central spans.

In rivers, the water shear on the underside of the ice cover is

usually the primary force acting on a boom. If the drag force

beyond five river widths upstream is not felt by the boom, the

water shear force per unit river width for a wide rectangular

channel can be determined by:

Water drag on

ice cover

7
8 COLD REGIONS TECHNICAL DIGEST NO. 96-1

f ySB w = γ water ice f 5 (2)

where γwater = the specific weight of water

yice = the average channel depth above the isoline of

maximum velocity

Sf = the friction slope

B = the average width of the ice cover on the reach

extending 3–5 boom widths upstream of the

structure.

Expressions for yice and Sf are given in the following:

 

y

n

n n

y

n

n

y ice

i

3/2

b

3/2

i

3/2 t

i

b

= t

+











 =

+ 



 

































−

1

1

3 2 /

where nb = the Manning’s roughness of the channel bed

ni = the Manning’s roughness of the ice cover

yt = the average under-ice flow depth.

S V n

R

c f

ice

= 2 2

4 3 2 22 . / (in English units)

where V = average under-ice water velocity

nc = the composite roughness for an ice-covered channel

Rice = the hydraulic radius.

3. Schematic showing

fractured ice area that

contributes to the ice

loading on a wide lake

ice boom.

Ice Boom

Open Water

on River

Unbroken Sheet Ice Cover on Lake

Fractured

Ice Cover

Current and Wind Direction

0 1000 ft

0 305 m

Shore

Shore

Current and Wind Direction

Unbroken Sheet Ice Cover on Lake
DESIGN OF ICE BOOMS 9

Table 2. Manning coefficients of roughness of the

bottom surface of initial ice covers (after Nezhikovsky

1964).

Initial Cover Cover

thickness formed from formed from Brash ice

 (ft) (m) loose slush frozen slush cover

0.3 0.1 — — 0.015

1.0 0.3 0.01 0.013 0.04

1.6 0.5 0.01 0.02 0.05

2.3 0.7 0.02 0.03 0.06

3.3 1.0 0.03 0.04 0.07

4.9 1.5 0.04 0.06 0.08

6.6 2.0 0.04 0.07 0.09

10 3.0 0.05 0.08 0.10

16 5.0 0.06 0.09 —

Using SI units, the 2.22 constant disappears. The composite roughness nc can be calculated from the Belokon-Sabaneev formula

(U.S. Army Corps of Engineers 1982):

n

n n c =  +









 i b

2

32 32 2 3 / / /

ni can vary from 0.01 to 0.10, depending on many factors, including ice cover type, thickness, piece size, temperature and age.

Table 2 gives ranges of values for different types of ice covers.

Under conditions where an ice cover will form behind a boom, ice

roughness will typically be in the 0.02–0.04 range.

The hydraulic radius Rice of the ice-covered channel can be

found from

R A

P P ice

bed ice

= +

where A = the under-ice flow area

Pice = the wetted perimeter of the underside of the ice cover

Pbed = the wetted perimeter of the channel bed.

For wide rectangular channels, the hydraulic radius can be approximated as one-half the under-ice depth.

If channel geometry data are available, standard step backwater models, such as HEC-2 with the ice cover option (U.S. Army

Corps of Engineers 1990), are extremely useful in determining

the hydraulic parameters used in the water shear calculation, since

HEC-2 output variables include water/ice surface slope, water

velocity, depth and channel top width.
10 COLD REGIONS TECHNICAL DIGEST NO. 96-1

Wind shear is not the predominant force in most river situations, since outside forces are generally not felt by a boom beyond

three to five river widths upstream of the structure. However, for

ice control structures on large lakes, such as the Lake Erie ice

boom, wind on the ice cover can be the most important driving

force.

For rivers, the wind force per unit width of boom can be estimated by

f C UB a d air = ρ 2 5 (3)

where Cd = the drag coefficient of air flowing over an ice cover,

in the range 1.7 – 2.2 × 10–3

ρair = mass density of air (2.5 × 10–3 slugs/ft3 at 32°F, 1.3

kg/m3 at 0°C)

U = wind velocity 33-ft (10 m) above the ice surface.

To estimate the extent of the ice area contributing to the wind load

on a wide lake ice boom, refer to Figure 3.

The downstream weight component of an ice cover results

from water surface slope, Sf. Since slope is usually mild at sites

where ice retention is possible (on the order of 0.001 to 0.0001),

the gravity component is relatively small. This force can become

significant if the ice cover is extremely thick, however. For rivers,

the gravity force acting on a unit width of boom is given by:

f e tS B g ice i f = − ( ) 1 5 γ (4)

where e = the porosity of ice cover, which is on the order of 0.5

for conditions of maximum loading (newly formed

freezeup jam, or accumulation of loose brash ice)

γice = specific weight of ice (57.2 lb/ ft3, 9000 N/m3)

ti = ice thickness

Sf = friction slope from Manning equation as defined above.

Because the boom units are relatively small, compared to the

cross section of the river, and the size of the ice cover, the drag

force on these units is generally negligible. In many ice boom

applications, the bottom of the ice cover is roughly even with the

bottom of the boom unit, rendering water drag on the boom unit

insignificant. If needed, the water drag force on the boom unit,

per unit river width, can be approximated from:

Wind drag on

 ice cover

Drag on boom units

Gravity force
DESIGN OF ICE BOOMS

f

ch V

d

D s w = ρ 2

2 (5)

where cD = drag coefficient for the submerged portion of the

boom unit (1.5–2.0 for rectangular shapes)

hs = submerged depth of boom unit

ρw = density of water (1.93 slugs/ft3, 1000 kg/m3)

V = average water velocity.

In general, the impact loads on an ice boom from a broken

cover are low. An exception occurs when an intact sheet upstream

of the boom is released in the form of floes that can be as large as

several acres. In most cases, large floes submerge the boom units

and override the ice boom. Relatively large forces can act on the

boom before it submerges, however. The impact of a large ice floe

typically does not occur when any of the other loads are present,

since large floes will be free to hit the boom only when the river is

relatively free of other ice. Impact loads may be distributed along

the length of the boom or analyzed as point loads. Distributed

over the boom width, the impact force can be expressed as:

f m V

L t i

ice = ∆

∆ (6a)

where L = length of the boom, perpendicular to the direction of

flow.

mice = mass of the ice floe

∆V = change in floe velocity, usually considered to end up

at rest

∆t = estimated time for the ice floe to come to rest.

Estimating the time required for the floe to come to rest may be

difficult. If the designer has an idea of the boom’s compliance, an

energy transfer approach can be used to estimate impact force per

unit width of river:

E fx m V

L = = i∆ ice∆ 2

2

where E is the energy transferred to the boom in the process of

stopping the floe, and ∆x is the distance required to stop the floe.

If we rearrange the equation, the impact force can be expressed

as:

Impact load from

broken cover

11
 COLD REGIONS TECHNICAL DIGEST NO. 96-1

f m V

x L i = ice ∆

∆

2

2 (6b)

The designer must determine the length over which this force is to

be distributed.

Large vessels navigating in winter can impose loads on an ice

boom in a number of ways. First, a vessel may collide directly

with the boom. Second, waves produced by a vessel passage can

result in both vertical and lateral movement of an intact sheet ice

cover, transmitting forces to the boom. The hydrodynamics of

boom loading due to vessel-induced waves are quite complicated

and beyond the scope of this technical digest. Third, waves or

propeller wash from a vessel may push broken ice pieces or brash

ice into a boom. The most common vessel effect takes place when

ship traffic in the vicinity of the boom breaks shore ice free,

allowing it to act on the boom. If the shore ice breaks into relatively small pieces, the increased ice load may be estimated by

increasing the ice area subject to water, wind and gravity forces

(eq 2, 3 and 4). If a large floe broken free by vessel passage moves

against the boom, it may be treated as an impact force and estimated using eq 6a and 6b.

Ice booms have been built in many configurations. Some booms

cross the entire channel width, while others stabilize or retain ice

only at the channel sides. The boom in Figure 2 has an opening for

ship passage. Figure 4 illustrates a variety of boom configurations. The upstream vee design shown in Figure 4e effectively

diverts arriving ice away from the highest velocity area at the

channel center and avoids the use of a midchannel anchor by

extending anchor cables to each shore. In more conventional configurations such as Figure 4b, the spacing between anchor lines is

typically 100 to 400 ft (30–120 m), depending on the loading and

the strength of the boom. Span lengths greater than 400 ft (Fig.

4c) are found in some debris boom applications, but are rare in

booms designed to retain ice.

In some applications, it may be advantageous to orient the

boom so that the region of maximum flow velocity does not

coincide with the area of maximum boom sag (Fig. 4e). In the

region of fastest current, the flow velocity component perpendicular to the boom will therefore be lower and the ice capture

efficiency increased. This arrangement also tends to divert ice

from the faster areas to slower parts of the channel, making it

easier for the boom to retain ice. Often, the part of the river with

Forces from vessel

passages

Typical ice boom

configurations

12
DESIGN OF ICE BOOMS 13

e. Upstream vee design

used on the Allegheny

River at Oil City in

Pennsylvania.

a. Conventional ice boom layout, showing components.

d. Spur boom

used to retain

and stabilize

an ice cover

at the channel

sides.

4. Typical ice boom layouts.

c. Single

span boom.

b. Multiple span

boom. Individual

spans are typically

100–400 ft (30–

120 m) in width.
14 COLD REGIONS TECHNICAL DIGEST NO. 96-1

the greatest depth and the highest current velocity is in the vicinity of the channel center. If the boom is oriented with the chord at

an acute angle to cross-stream direction, the point where the

boom is perpendicular to the flow is shifted away from the path of

maximum surface velocity (Fig. 4e and 5).

The following discussion is based on boom geometry as shown

in Figure 6. Relationships exist between the location of the anchor

points, the unstressed length of wire rope S0, the sag ratio s, and

the tension in the main support cable T. The sag ratio is defined as

the ratio of the midspan deflection, dmidspan, to the perpendicular

length L. Assuming a uniform loading across the river width

results in a parabolic shape for the ice boom cable. For most

applications, this shape is a reasonable approximation of the actual ice boom geometry.

Geometry of

boom and wire

rope tension

Ice Boom

Cable

20 ft

(6 m)

PLAN VIEW

3 ft

(0.9 m)

2 ft

(0.6 m)

Connector

Chain

END VIEW

Flow

Boom

Cable

Salmon

River

Boom Units

1990-'91

Approximate Path of 

Maximum Surface Velocity

0 100 ft

0 30.5 m

Boom Units

5. Salmon River boom.

Note that the boom is

aligned at an angle to

the path of maximum

surface water velocity.
DESIGN OF ICE BOOMS 15

Assuming a parabolic shape and an inextensible cable (Leonard

1988), the relationship among the unstressed length S0, the sag

ratio s, and the perpendicular chord length L may be approximated by:

SL s 0

2 2 1 8

3

1

2

=++ 





 tan θ (7)

The x-component of the load H along the boom cable is constant

and is given by:

H pL

s = 8 (8a)

The y-component of the load V in the main cable at any horizontal

distance x is given by:

V H pL x

L

= +− 





 tanθ

2

1 2 (8b)

Equations 8a and 8b can be combined to give a relationship that

approximates the resultant tension, T, at any point x:

T pL

s

s

x

L

= + +− 











 



 8

1 41 2 2

tanθ (9)

Calculation of main

cable tension

θ

P = Uniform

x

y

dmid-span

Flow

L tan θ

H

H

V1

T1

T0

V0

L

6. Definition sketch for

ice boom loading and

geometry. A uniform

loading is assumed

across the channel

width to produce a

parabolic shape.
16 COLD REGIONS TECHNICAL DIGEST NO. 96-1

where p is the uniform load on the boom per unit width of river

(= fb as computed above in eq 1) and θ is the angle between the

chord and the line perpendicular to the direction of force.

The complete geometry of the boom cable may be approximated

by:

yx s

x

L

= +− 











 



 tanθ 4 1 (10)

Several considerations affect the choice of a wire rope. First,

and most important, published wire rope strengths are considered

to be breaking, and not working strength, so a factor of safety is

needed. Table 3 lists the load carrying capacity of common sizes

and types of galvanized wire rope. Second, standard hoisting rope

(6 × 19 construction)* is recommended for booms because of its

high strength, good wearing characteristics, and availability. Third,

* 6 × 19 means that the rope is composed of six strands, and each strand is made

up of 19 wires.

Table 3. Nominal strength of 6 × 19 galvanized improved plow steel

wire rope.

Nominal strength (tons)*

of 2,000 pounds

6 × 19 galvanized Approximate weight

Diameter Diameter improved plow steel per foot (lb)**

(in.) (mm) Fiber core IWRC† Fiber core IWRC

1/4 6.3 2.47 2.65 0.105 0.116

5/16 7.9 3.83 4.12 0.164 0.180

3/8 9.5 5.49 5.90 0.236 0.260

7/16 11.1 7.44 8.00 0.32 0.35

1/2 12.7 9.63 10.30 0.42 0.46

9/16 14.3 12.10 13.00 0.53 0.59

5/8 15.9 15.00 16.10 0.66 0.72

3/4 19.0 21.40 23.00 0.95 1.04

7/8 22.2 29.00 31.10 1.29 1.42

1 25.4 37.60 40.40 1.68 1.85

1-1/8 28.6 47.30 50.90 2.13 2.34

1-1/4 31.7 58.10 62.50 2.63 2.89

1-3/8 34.9 69.90 75.10 3.18 3.50

1-1/2 38.1 82.80 89.00 3.78 4.16

1-5/8 41.3 96.30 103.00 4.44 4.88

1-3/4 44.4 112.00 120.00 5.15 5.67

2 50.8 144.00 155.00 6.72 7.39

This type of information can be found in many engineering handbooks or suppliers

catalogs. The above is taken from Washington Chain and Supply, Inc., 2901 Utah

Ave. South, Seattle, Washington 98124.

* 1 ton of 2000 lb = 1.102 metric tonnes

** 1 lbmass = 0.4534 kg

† IWRC = independent wire rope core

Choice of wire rope
DESIGN OF ICE BOOMS 17

flexible fiber core wire rope should be used for members to be

handled by heavy equipment. Fourth, because members are constantly wet, galvanized wire rope is used to minimize damage

from corrosion. Fifth, because wire rope sizes over 2–3 in. (5–7.5

cm) in diameter are very difficult to handle, the structural load

and therefore the wire rope size can be reduced by shortening the

span length of the boom cable.

For midstream river-bottom anchors, the anchor cable should

have a minimum “scope” of 7 (7 horizontal to 1 vertical). The

Engineer Manual, Ice Engineering (U.S. Army Corps of Engineers 1982) recommends a scope of 12. This allows the structural

system to absorb impact loads while maintaining a relatively

horizontal load on the anchors. These midstream anchors can take

many forms, such as ship anchors, driven piles, drilled and grouted

piles, and buried steel plates. Examples of anchor types are shown

in Figure 7. If the year-round river use conditions allow, perma7. Anchor types

illustrated.

b. Buried concretefilled pipe used as land

end anchor. Note Ibeam reinforcement.

a. Deadman and

pedestal type anchor

used at the land end.

c. Sheet-piling cell

serving as a midchannel anchor.

Anchoring systems
 COLD REGIONS TECHNICAL DIGEST NO. 96-1

f. Anchor constructed of steel weldment grouted to

drilled hole in bedrock (midchannel or land)

g. Anchor constructed of driven H-piles

(midchannel or land)

7 (cont’d). Anchor types illustrated.

d. Ballasted steel mud

anchor (midchannel).

e. Chain anchor

grouted to drilled hole

in bedrock (midchannel).

18
DESIGN OF ICE BOOMS 19

nent above-water anchors, such as rock islands, sheet-pile cells,

and timber and rock cribs can be used. These above-water anchors

provide the added benefit of increasing the overall stability of a

sheet ice cover.

Anchor lines are generally made of wire rope. However, if the

boom is being used in a large water body with commercial navigation, anchor lines of high strength anchor chain may be preferable, because a chain being more flexible will lie on the bottom

without coiling. Furthermore, a chain is more resistant to abrasion

if the bottom is rocky.

If the boom has midstream anchors, a junction plate must be

used to connect the two boom cables to the single anchor cable.

Because these junction plates must be designed for high loads,

they usually require additional flotation to support their weight

and prevent the boom from submerging near the anchor attachment points. This additional flotation is also needed to support

parts of the submerged weight of the anchor cable and the adjacent boom cables. Figures 8 shows a typical junction plate design,

and Figure 9 shows a typical junction plate and float arrangement.

8. Example of junction

plate design. Note the

reinforcing steel plates

welded to each side of

the three holes.
20 COLD REGIONS TECHNICAL DIGEST NO. 96-1

Boom unit design

Ice restraint

capacity

Important considerations in the design of the actual boom units

are the type and thickness of the ice to be retained and the anticipated ice forces. The strength of the boom unit is also important,

since a boom unit must resist bending failure under the design

loads, particularly if large floes are expected to impact the structure. In addition, the boom unit must have sufficient frontal area

to capture floating ice and debris. Size is also an issue, because a

boom unit must be small enough to be easily handled by available

equipment during its annual installation and removal.

The ice restraint capacity of a boom unit depends on the buoyancy, the righting moment, the location of the anchor connection,

and the type of ice being retained. Figure 10, based on experimental data with thin ice covers, shows that a single 1 × 2 ft (0.3 × 0.6

m) timber boom, with a scope of 12.5 or more, has a maximum

load capacity in the 80 lb/ft (1.2 kN/m) range, above which the tilt

angle β reaches about 35°, resulting in the ice overriding the

boom unit. With thicker, stronger ice covers, much higher loads

are possible, however. Some double pontoon booms have load

capacities as high as 500 lb/ft (7.3 kN/m). Measured force levels

listed in Table 1 give an idea of the maximum ice restraint capacities of various other types of booms.

Table 1 and Figure 11 illustrate a variety of successful boom

unit designs. Many others are possible. For years, single timber

boom units (Fig. 11a) have been successfully used in both large

Successful ice

boom designs

9. Example of junction

plate and float arrangement. In this case

a cylindrical float

supports the junction

plate with a 4-ft (1.2-m)

length of chain.

1 1/2” (38 mm) ø

Eyebolt 1” (25.4 mm) Shackle

2” (51 mm) Boom Cable

2” (51 mm)

Wire Rope Socket

A - A 2”

(51 mm)

1/2” (13 mm) Bolt

Cylindrical

Buoy

Steel

Band

A

A

Stiffener

5’

(1.74 m)

3’

(0.9 m)

4”

(102 mm)

7/8” (23 mm) x 4’ (1.22 m) Chain
DESIGN OF ICE BOOMS 21

and small rivers. Douglas fir has been the timber of choice because of its strength and durability, particularly under conditions

of constant wetting. Many of these booms were designed using 12- ×

14-in. (30- × 36-cm) timbers, often in parallel, separated by timber blocks or steel struts, to increase the righting moment (Fig.

11b). In addition, some of these units have a second timber installed on the upstream face to increase the depth of the boom and

the capture efficiency (Fig. 5). The lengths of these timber boom

units are generally in the 20- to 30-ft (6- to 9-m) range, and the

spacing between boom units is optimum at about three to six ice

thicknesses. Timber booms have to be periodically removed from

the water to allow for complete drying.

Douglas fir timbers are still being used on Lake Erie, the International Section of the St. Lawrence Seaway, and at Lake St.

Peter on the lower St. Lawrence River. However, the Canadian

Coast Guard and Hydro-Quebec are switching to steel pontoons

due to their lower maintenance costs and the decreasing availability of large Douglas fir timbers. The steel boom units may be

rectangular as shown in Figure 11c, or may use steel pipe as the

flotation members as shown in Figure 11d and 11f. Some steel

pontoon booms are filled with foam to maintain floatation in the

event of damage and leaks. In this case, additional floatation is

needed to compensate for the added weight of the foam. Often, a

vertical face is installed on the upstream face of a pipe boom unit

(Fig. 11f), particularly in the case of shear booms. Recently, the

Canadian Coast Guard has had success with single-circular10. Ice restraint capacity of a rectangular timber boom. Note that tan–1

(0.08) = 4.6° so the boom

chain is nearly horizontal. For the thin ice case,

the maximum ice restrain capacity of a rectangular timber boom is

on the order of 50–80

lb/ft (0.73–1.2 kN/m).
22 COLD REGIONS TECHNICAL DIGEST NO. 96-1

a. Single rectangular

timber boom. Typical

dimensions are 14 × 22

in. (36 × 56 cm).

11. Successful ice boom unit designs.

b. Boom constructed of

double timbers connected with steel angles

c. 2.5 × 5.5 ft (0.75 ×

1.5 m) rectangular

steel pontoon as used

on the Allegheny

River at Oil City,

Pennsylvania.

e. Boom unit constructed of plastic

pipe, banded to the boom cable with

wire hoops.

d. Circular steel pontoon

boom, 30-in.- diam. (76-

cm), as used on Lake St.

Peter on the lower St.

Lawrence River.

f. Double steel pipe

pontoon booms used

on the Beauharnois

Canal. Pipe diameter

in 3 ft (0.9 m). This

boom withstood a

maximum measured

force of 3.2 kip/ft (47

kN/m).
DESIGN OF ICE BOOMS

section steel pipe booms on the lower St. Lawrence River (Fig.

11d). Plastic tubing has also been used (Fig. 11e). For additional

examples of possible boom cross-sectional geometries, refer to

the Ice Engineering (U.S. Army Corps of Engineers 1982).

The boom unit is generally connected to the main load carrying

cable by a 3- to 5-ft (0.9- to 1.5-m) length of chain or wire rope

(Fig. 12). The location of the chain-to-boom-unit connection affects the righting moment, but structural considerations are equally

important. The boom unit connector chains attach to cable clamps

on the main span cable. Special steel saddles must be fabricated to

protect the main wire rope from being pinched by the cable clamps

(Fig.13). Figure 14 shows standard fittings useful in the design of

ice boom connections. Included are open and closed spelter sockets used to link wire rope to various fittings such as shackles,

chains, and connector plates.

If one boom component fails, the load on adjacent components

will increase substantially. A failure analysis should therefore be

made on the multicomponent structure to examine the effect on

adjacent members, should one member fail. Fuse-links, or speFailure

considerations

Boom unit

connections

12. Triple timber ice

boom unit, showing

connections to main

cable.

23

13. Fabricated steel

saddles, designed to protect the main wire rope

from pinching by the

cable clamps.
 COLD REGIONS TECHNICAL DIGEST NO. 96-1

Shackles Chain Connector Plate

Open Spelter Socket Closed Spelter Socket

14. Standard fittings

useful in the design of

ice boom connections.

cially designed weak points, may be incorporated in the design,

permitting individual boom components to fail in a way that

prevents failure of the entire structure. For example, a fuse link at

one end of the boom cable would allow the span to open, reducing

the force on the anchor cable. In contrast, if the anchor cable is

allowed to fail first, the increased load on the adjacent anchor

cables might cause their failure as well.

This example is based on an ice boom system designed for the

Allegheny River Lock and Dam 8. Figure 15 shows a plan view of

the river area upstream of the lock and dam. An elevation of the

free overflow weir is shown in Figure 16. Average discharge

values for the site are listed in Table 4.

The boom at this location is designed to be at an angle with the

flow, providing for an ice and debris opening, which allows brash

ice from the ship track to be flushed over the weir without clogging the lock entrance.

Since a boom is effective at Froude numbers less than 0.08, one

approach is to determine the depth, discharge, and average velocity at this Froude number. This can be achieved by combining the

weir and continuity equations with the definition of the Froude

number. The calculated discharge is then checked against the

observed average winter discharges listed in Table 4. Discharge

over a weir can be estimated by:

Q CL H = w 3 2/

where C = weir discharge coefficient, which varies between 2.5

and 3.5 depending upon the type of weir (3.3 will be

used in this example)

Design example

Chain connected to wire rope by 

shackle and closed spelter socket

24
DESIGN OF ICE BOOMS 25

15. Plan view of the

river area upstream of

the Lock and Dam 8 on

the Allegheny River.

The boom is made up of

five, 168-ft (51-m) spans

aligned at a 26.5° angle

to the cross-channel

direction.

16. Elevation view of a

free overflow weir.

Table 4. Monthly average discharges for Allegheny River.

December January February March

(ft3/s) (m3/s) (ft3/s) (m3/s) (ft3/s) (m3/s) (ft3/s) (m3/s)

MEAN 27,460 777 38,460 1090 17,550 497 54,950 1556

MAX 44,100 1250 88,500 2506 52,500 1486 99,200 2807

MIN 15,200 430 18,800 532 7,450 211 23,500 665

5 @ 168’

26.5°

0 + 56 9 + 53

100’

Debris Opening

Flow

Dam

Lock
 COLD REGIONS TECHNICAL DIGEST NO. 96-1

Lw = the length of the weir, which is 883 ft* for this example

H = the flow depth over the weir.

Assuming upstream channel width is roughly equivalent to the

weir length Lw, average velocity upstream of the dam can be

expressed as

V Q

A

CL H

L D = = w

w

3 2/

where D is the flow depth of the river upstream of the dam. Using

the elevations presented in Figure 16, the height of the weir =

745.0 – 726.5 = 18.5 ft. The upstream depth is then D = 18.5 + H.

Combining these gives:

F V

gD

CL H

L D gD R == ≤ w

w

3 2

0 08

/

.

0 08

18 5 18 5

3 2

. . .

/

≥

( + ) ( + )

CH

Hg H

=

( + ) ( + )

= ( ) +









3 3

18 5 18 5

0 5815

18 5

3 2 3 2 .

. . . .

/ / H

Hg H

H

H

Solving for H by trial and error gives:

H ≤ 6.7 ft

The average depth (D) upstream of the weir, at a Froude number

of 0.08 is then:

D = 18.5 + 6.7 = 25.2 ft

Discharge and average velocity at the boom location can then be

calculated:

Q = CLH3/2 = (3.3) (883) (6.7)3/2 = 50,500 ft3/s

Average velocity is then:

*Only English units are used in Design Example.

26
DESIGN OF ICE BOOMS

V Q

A

Q

LD == = ( )

= 50 500

883 25 2

2 3 3 ,

().

. / ft s

From Table 4, 50,500 ft3/s is a reasonable winter discharge.

Periods of higher discharge are possible, however. Under these

conditions, Froude number and water velocity may be too high

for successful ice retention by the boom. During the high discharge periods, measures such as raising the pool height or upstream flow control may be necessary.

An alternative method would be to select a maximum expected

winter discharge, find the water depth using the weir equation,

then check if the FR ≤ 0.08 and V ≤ 2.3 ft/s criteria are satisfied. If

channel cross-section geometry data are available, numerical models such as HEC-2 (U.S. Army Corps of Engineers 1990) are

helpful in determining hydraulic conditions over a range of discharges at potential ice boom locations.

For this example, the following values of various parameters

are assumed: channel bed roughness nb = 0.02, ice roughness ni

 =

0.03, brash ice cover thickness ti

 = 0.75 ft and porosity e = 0.5.

The average width of the upstream ice cover contributing to the

load on the boom is assumed to be 900 ft.

Under-ice depth: yt

 = D – 0.92 ti = 25.2 – (0.92) (0.75) = 24.5 ft

For wide rectangular channels, under-ice hydraulic radius (Rice )

can be approximated as half the under-ice depth:

R y ice t = = 0 5 0 5 24 5 12 2 . .. . ( )( ) = ft

The composite roughness for the ice covered channel (nc) can be

calculated using the Belokon-Sabaneev formula:

n

n n

c i b

2 =

 +











( ) + ( ) 













 =

32 32 2 3 3 2 3 2 2 3

0 03 0 02

2

0 025

/ / / / / / . . .

Friction slope (Sf) may now be calculated:

S V n

R

f c

ice

4/3 4/3 = = ( ) ( )

( )( ) = 2 2 2 2

2 22

2 3 0 025

2 22 12 2

0 000053 .

. .

. . .

To find the shear stress on the underside of the ice cover, the

average channel depth above the isoline of maximum velocity

(yice ) is needed:

27
 COLD REGIONS TECHNICAL DIGEST NO. 96-1

y

n

n n

y i

b i

ice t

3/2

3/2 3/2 = ft

+











 = ( )

( ) + ( )











 ( ) =

3 2

32 32

0 03

0 22 0 03

24 5 1 59

/

/ /

.

. . . .

The shear stress on the underside of the ice is computed using eq 2:

fw = γwater yiceSf5B = (62.4)(15.9)(0.000053)(5)(900) = 237 lb/ft

The wind drag forces are then determined from eq 3, assuming a

critical wind of 25 mi/h (or 37 ft/s) in the direction of the river

flow. Using a drag coefficient Cd of 2.2 × 10–3 and a mass density

of air ρair of 2.5 × 10–3 slugs /ft3:

fa = CdρairU25B = (2.2×10–3)(2.5×10–3)(37)2(5)(900) = 34 lb/ft

Equation 4 gives the gravity forces exerted by the ice cover on a

unit width of boom:

fg = yice(1–e)ti

Sf5B = (57.4)(1–0.5)(0.75)(0.000053)(5)(900) = 5 lb/ft

With a 0.75-ft-thick ice cover, the ice bottom will be roughly even

with the bottom of a typical boom unit. Water drag on the boom

unit is neglected in this design case.

For impact loading, it is assumed that the boom units displace

an average distance of 10 ft while stopping a 2-acre × 1-ft-thick

ice floe moving with an initial velocity equal to the average current velocity at 2.3 ft/s. The impact force fi

 is considered separately, since a large floe would probably not impact the boom if

an ice cover is already in place. From eq 6b:

f m V

d i

ice

2 = = lb ( )( )( )( )( )

( ) = ∆ 2 2 2 43 560 1 0 92 1 93 2 3

2 10

40 900 , ... ,

If the floe is roughly square in shape, the length of one side would

be approximately 300 ft. Distributing the impact load over this

length gives:

40 900 136 , lb

300 ft = lb/ft along the contact area

Neglecting vessel-induced forces, water drag on the boom unit,

and the ice impact forces, the total force acting on the boom fb is

the sum of these forces:

fb = fw + fa + fg = 237 + 34 + 5 = 276 lb/ft (say 280 lb/ft)

28
DESIGN OF ICE BOOMS

With the design loads determined, the cable tensions can be

computed. It should be noted that a sag ratio s is usually in the

range of 0.15–0.20. This range generally allows the midstream

anchor cables to be the same size as the main boom cables. With

lower sag ratios, the tension and, therefore the wire rope diameter,

may become prohibitively large. With higher sag ratios, the tension decreases, but the length of the wire rope increases. The

increased length may require additional boom units, which would

result in higher costs.

Assuming that the downstream deflection of the boom is 32 ft,

s would be:

s

d

L = == midspan ft

ft

32

168

0 19 .

The wire rope tension is then computed for both ends of the cable

using eq 9.

T pL

s

s

x

L

= + +− 











 



 8

1 41 2 2

tanθ

T0

280 168 2

8 0 19 = 1 26 5 4 0 19 1 0 49 750 ( )

( ) + + [ ] ( )( ) = . tan . . – , lb

T1

280 168 2

8 0 19 = 1 26 5 4 0 19 1 2 32 000 ( )

( ) + + [ ] ( )( ) = . tan . . – , lb

Using the maximum tension of 50,000 lb and a factor of safety

of 3.5 gives a boom cable tension of 175,000 lb or 88 tons.

From Table 3, a 1-1/2-in.wire rope of galvanized improved

plow steel-fiber core (GIPS-FC) 6 × 19 construction with a breaking capacity of 82.80 tons would provide a factor of safety of 3.3.

The next largest wire rope diameter (1-5/8 in.) with a breaking

strength of 96.30 tons would increase the factor of safety to 3.9.

The length of the boom cable can be found from eq 7:

SL s 0

2 2 1 8

3

1

2

=++ 





 tan θ

2 2 168 1 8

3

0 19 1

2 = ( ) + ( ) + (26 5 205 ) 





 . tan . = ft

The final “eye-to-eye” cable length has to be determined after the

junction plates have been designed.

29
30 COLD REGIONS TECHNICAL DIGEST NO. 96-1

The horizontal load on the midstream anchors Tanchor will be

the load acting on a tributary width of half of the wire rope span

on either side of the anchor:

Tanchor = fb(tributary width) = 280(168)(0.5 + 0.5) = 47,040 lb

Use a 1-1/2-in. 6 × 19 GIPS-FC wire rope with a breaking capacity of 82.8 tons. With a depth of 25 ft and a scope of 7 horizontal

to 1 vertical, the anchor cable length would be 175 ft.

Floats must be designed to support the half of the weight of the

anchor cable and adjacent boom cables, as well as the weight of

the junction plates and connections. Figures 1 and 9 show typical

float arrangements. Table 2 gives a weight of 3.18 lb per lineal

foot for 1-3/8 in. 9 × 16 GIPS-FC wire rope. The boom cable

weight is then:

205 ft × 3.78 lb/ft = 775 lb

and the anchor cable weighs:

175 ft × 3.78 lb/ft = 662 lb

Assume the junction plate with wire rope connections weighs

100 lb and the float weighs 150 lb. The float at each junction must

supply a buoyant force (Fb) adequate to support its own weight,

the submerged weight of the junction plate and half the submerged weight of the anchor cable and adjacent boom cables:

fb

steel water

steel

= + lb  −



 



 + ( ) + ( ) + ( ) 



 



 150 100 662 775 775 1200 = 1

2

1

2

1

2

γ γ

γ

where γsteel = 490 lb/ft3 and γwater = 62.4 lb/ft3.

The volume of water (Vw) displaced to provide this buoyant force is

V W w w

w

3 == = ft

γ

1200

62 4

19 2 . .

Assuming that 40% of the float’s volume is submerged under static conditions, the total volume of the float must be 19.2

ft3/40%, or 48 ft3. A 3-ft-diam. × 6-ft-long cylindrical float, with

a volume of 42.4 ft3 would work in this case.

Conventional ice boom units are generally 20–30 ft long, with

a spacing between units of 3–6 times the ice thickness. For each

205-ft-long main span cable, eight 20-ft-long boom units with

5.0- ft gaps between units would work well. A smaller gap width

could be achieved by using nine 20-ft booms with 2.5-ft gaps.

fb

steel water

steel

= + lb  −



 



 + ( ) + ( ) + ( ) 



 



 150 100 662 775 775 1200 = 1

2

1

2

1

2

γ γ

γ
DESIGN OF ICE BOOMS 31

At this point, the design of the main structural components of

the boom is complete and anticipated force levels on anchor and

connection systems are known. Typical types of connections are

discussed earlier in the technical digest and contractor catalogs

provide their working strength limits. Anchor system design alternatives are illustrated in Figure 7. Detailed anchor design depends

on geotechnical conditions at the site, such as sediment type and

depth to bedrock. These issues are beyond the scope of this

report, however.

Sample ice boom designs may be obtained upon request by

contacting the Ice Engineering Research Division at the U.S.

Army Cold Regions Research and Engineering Laboratory, 72

Lyme Road, Hanover, New Hampshire 03755, (603) 646-4378.

The authors thank the following people. Anthony Mamone

assisted in the initial organization, Kevin Carey and F. Donald

Haynes provided technical reviews, and Edmund Wright served

as technical editor.

Abdelnour, R. , R.D. Crissman, G. Comfort (1994) Assessment

of ice boom technology for application to the Upper Niagara

River. In Proceedings or the IAHR Symposium on Ice, 23–26

August 1994, Trondheim, Norway, vol 2. p. 734–743.

Leonard, J.W. (1988) Tension Structures: Behavior and Analysis. New York: McGraw-Hill.

Michel, B. (1978) Ice Mechanics. Quebec: Les Presses de

l’Université Laval.

Nezhikhovsky, R.A. (1964) Coefficient of roughness of bottom

surfaces of slush ice cover. Soviet Hydrology: Selected Papers,

no. 2, p.127–150

Perham, R. (1983) Ice sheet retention structures. USA Cold Regions Research and Engineering Laboratory, CRREL Report 83-30.

Tuthill, A. (1995) Structural ice control: Review of existing methods. USA Cold Regions Research and Engineering Laboratory,

Special Report 95-18.

U.S. Army Corps of Engineers (1982) Ice Engineering. USA

Corps of Engineers, Office of the Chief of Engineers, EM1110-2-

1612, 15 Oct. 1982.

U.S. Army Corps of Engineers (1990) HEC-2 water surface

profiles. USA Corps of Engineers, Hydrologic Engineering Center, Davis, California.

White, K.D. (1992) Salmon River experimental ice boom 1989–

90 and 1990–91 winter seasons. USA Cold Regions Research and

Engineering Laboratory, Special Report 92-20.

Acknowledgments

Literature cited