ICE JAM MITIGATION MEASURES

Figure 20. Schematic of on-line data retrieval at branch site

Permanent measures

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Home Base

File transfer over modem.

Download database to remote site.

Ice Database

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File transfer over internet.

Download database to remote site.

Home Base

Figure 21. Schematic of complete data download before processing.

communication cost for downloading (no session

extent of damages justifies their cost. Although

costs). The disadvantages are that data may need

the majority of the structural mitigation tech-

to be downloaded repeatedly to stay current, and

niques are, by their very nature, permanent, some

local changes to the database are not reflected

are designed to be removable. These removable

at the home base.

structures are usually installed at the beginning

of winter and removed after spring breakup, when

the threat of ice-jam flooding no longer exists.

Nonstructural measures are those that modi-

ICE JAM MITIGATION

fy vulnerability to flooding or reduce the sever-

MEASURES

ity of ice-jam-related floods. They are generally

A number of ice jam flood mitigation mea-

less expensive than structural solutions. The

sures are possible, depending on the type, length,

majority of the nonstructural techniques are

thickness and accessibility of the jam and the avail-

used for advance and emergency measures

able equipment, personnel and budget. These

when serious ice-jam flooding is imminent or

measures may be broadly labeled as structural or

already occurring. For example, ice weakening

nonstructural; as measures appropriate to control

(ice cutting or dusting) may be implemented be-

breakup or freeze-up jams; and finally, as mea-

fore an ice jam occurs, if sufficient warning is

sures that are permanent, deployed in advance of

provided, while blasting and mechanical removal

an anticipated flood threat, or deployed under

are often employed as emergency mitigation mea-

emergency conditions when a jam has formed and

sures once ice jams have occurred. On the other

flooding has occurred. A brief overview of possi-

hand, the creation of ice-storage zones upstream

ble mitigation measures is followed by a discus-

from a known jam site (to minimize the amount

sion of measures that might be applied in the

of ice reaching the jam site) can be considered a

study area.

permanent measure, since these areas, once es-

Structural measures for ice-jam control, such

tablished and properly maintained, can be used

as levees, dikes and floodwalls, may incorporate

year after year.

features that can be used to alleviate open-water

Freeze-up ice-jam control usually targets the

flooding as well. The costs of such measures in-

production and transport of the frazil ice which

clude construction, operation and land acquisi-

makes up the jam. This may be accomplished by

tion, as well as costs associated with recreation

encouraging the growth of an ice cover, which

and environmental mitigation. Unfortunately,

insulates the water beneath, decreasing the pro-

while they are often very successful, structural

duction of frazil ice. The ice cover can also incor-

solutions tend to be expensive, and current bud-

porate frazil ice which is transported from up-

get climates make their funding less likely. They

stream production areas, decreasing the supply

remain appropriate for rivers where chronic or

available to jam or deposit beneath a downstream

particularly serious threats persist and where the

ice cover.

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