able when needed. The Nebraska Disaster and
Construction equipment can be used to break
Civil Defense Act is attached in Appendix C for
up an ice cover or an existing jam, either from the
reference. The act defines the legislated powers
shore or, if the ice is safe, from the river itself. It is
and duties of the Nebraska State Civil Defense
generally best to begin working from the down-
Agency. Appendix D contains a legal opinion
stream end of the ice cover toward the upstream
drafted by the State indicating that both the State
end so that the broken ice will be carried away. A
and its political subdivisions are essentially pro-
heavy weight or wrecking ball can be dropped
tected from liability if emergency measures are in
repeatedly on the ice surface to break up the ice.
accordance with the Nebraska Disaster and Civil
Ice can be broken either to form a channel or to
Defense Act and an emergency has been declared.
weaken the ice in specific locations.
Prior to implementing emergency measures, it
Mechanical removal involves taking the ice out
is necessary to monitor the river ice conditions
of the river and placing it elsewhere using bull-
upstream as well as downstream from the jam
dozers, backhoes, excavators or draglines, start-
site to select the best measures and to eliminate
ing from the downstream end of the ice accumu-
those that may only displace the flooding prob-
lation. This approach is most effective on small
lem to another location. Early ice monitoring can
rivers and streams because of the time required to
also provide some lead time to allow other emer-
excavate and because of additional safety con-
gency measures to be taken. Downstream ice con-
cerns associated with wide or deep rivers. Me-
ditions also need to be assessed, if only to deter-
chanical removal can be expensive and slow but
mine whether there is sufficient open-water area
also quite effective. Access to the jam site by heavy
to receive ice when the jam releases.
equipment is frequently an impediment to me-
If ice-jam flooding has been predicted, levees
chanical removal of ice.
should be closed immediately and interior drain-
Often a popular solution to ice-jam problems,
age pumps should be prepared for possible acti-
blasting breaks up an ice cover or loosens an ice
vation. Again, winter weather conditions such as
jam so that it is free to move. Absolute prerequi-
snowdrifts or frozen valves, which can hinder
sites to successful blasting are that enough flow is
levee closing, should be identified. Monitoring of
passing down the river to transport the ice away
water levels at levees may aid in identifying pos-
from the site and that sufficient open-water area
sible overflow sites before serious damage can
exists downstream to receive the ice. Otherwise,
occur.
the ice will simply rejam elsewhere and cause
Although ice can cause significant damage to
problems for another community. Blasting has
sandbags used as protective barriers, the use of
been used to create a relief channel within a
sandbagging as an emergency response measure
grounded jam to pass water and decrease the up-
can be very effective in reducing damages at par-
stream water level. As with icebreaking and me-
ticular facilities or locations. For example, sand-
chanical removal, it is recommended that blasting
bagging around sewage treatment plants or low
proceed upstream from the toe of the jam. Safety
points on roads or riverbanks can significantly
and environmental concerns must be addressed
reduce flood losses. Overbank flow may be chan-
before implementation (USACE 1982).
neled away from flood damage areas using tem-
porary levees constructed of sandbags.
Specific mitigation options
Ice-jam emergency response measures include
within the study area
icebreaking, mechanical ice removal and ice blast-
The choice of mitigation options for a particu-
ing, in addition to the traditional flood-fighting
lar ice-jam location depends on a number of fac-
efforts of evacuation, levee closing and sandbag-
tors, including the characteristics of the ice jam,
ging, all of which also qualify as advance mea-
weather, access and budget. Local residents and
sures. The principle behind evacuation is to move
officials, who are most familiar with the jam,
people at risk from a place of relative danger to a
should be involved in selecting appropriate miti-
place of relative safety via a route that does not
gation measures. Applying traditional flood miti-
pose significant danger. Local law enforcement
gation techniques (e.g. floodproofing, sandbag-
departments usually serve as lead organizations
ging, evacuation and levee closing) should be
and have standard operating procedures. Winter
considered for areas affected by ice-jam flooding
weather conditions should be taken into account
Increased monitoring and detection of ice con-
when planning evacuation timing, equipment and
ditions, breakup and jamming is a nonstructural
routes.
mitigation option that should be implemented at
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