Following the March 1993 ice event, the Feder-
This guidance is applicable to the overall study
al Emergency Management Agency (FEMA), Re-
area as well as to the seven sites shown in Figure
gion VII, as required by 44 CFR Part 206, formed
1. In addition, the study includes an assessment
an Interagency Hazard Mitigation Team to review
of possible mitigation measures that may be suit-
the flood events and suggest measures which
able for implementation at different locations.
might be implemented to mitigate similar events
Based on an analysis of past ice, meteorological
in the future. At the suggestion of representatives
and hydrological records, an initial predictive
from State agencies, Work Element 3 called for a
model of ice-jam occurrence and severity was de-
comprehensive investigation by the Corps of En-
veloped. Because data collection is important in
gineers to gather historical ice data with the in-
detection, warning and the refinement of the pre-
tent of developing guidance that could be used to
dictive model for ice jams, a plan for collecting
mitigate or alleviate recurring ice-jam-related
future ice-related data was designed.
flooding on the Lower Platte, Loup and Elkhorn
Rivers.
The Governor enthusiastically supported the
HISTORICAL DATA
concept, and after a series of meetings, the planned
scope of the Section 22 study was defined. The
Collection of data from past ice events is nec-
State's share of the funding was provided by the
essary in order to characterize the ice jams or oth-
Governor 's Emergency Fund and the Natural Re-
er ice events at the chosen sites as well as those
sources Commission. The present study is the re-
occurring within the region as a whole. Analysis
sult of this hazard mitigation coordination.
of historical ice records and meteorological and
The objective of the Corps' year-long Section
hydrological data enables us to determine which
22 study (authorized by Section 22 of the Water
parameters affecting jam formation and progres-
Resources Development Act of 1974, as amended)
sion are most important. Although ice events are
was to investigate the recurring ice-jam problems
usually highly site-specific, there may be similari-
in the Lower Platte, Loup and Elkhorn Rivers with
ties between ice events that occur within a region.
the goal of developing general guidance on the
It is these similarities that allow development of
likelihood of ice-jam occurrence and evaluating
general guidance on mitigation measures as well
potential ice-jam flood mitigation measures. Sev-
as a regional ice-jam predictive model.
en locations of recurring ice jams were chosen for
Ice event records are often more difficult to
study following the recommendations of the In-
obtain than open-water flood records. Informa-
teragency Hazard Mitigation Team. These loca-
tion on ice events is lacking because most ice
tions are shown in Figure 1.
events occur less frequently than open-water
There are a number of sites which experience
floods, ice events are often short-lived and may
ice jams and ice-jam-related flooding in addition
affect only a short reach of river, and access or
to the seven sites identified above, including
weather conditions can make it difficult to make
Schuyler, Ames and Louisville on the Platte River
observations. Ice events can include:
and Norfolk, Waterloo and West Point on the
Ice jams that cause flooding (overbank);
Elkhorn River. Many of these sites have also ex-
Ice jams that do not cause flooding (within
perienced damaging open-water flood events and
bank) that may not be identified as ice jams;
have put into place mitigation measures ranging
Ice covers that raise water levels upstream
from nonstructural measures such as detection,
or decrease water levels downstream;
monitoring, warning and emergency response
Initial ice cover formation; and
plans to structural measures such as levees and
Ice cover breakup and movement.
dikes. These mitigation measures have been pri-
Ice jams include those which occur in the early
marily designed for open-water events, although
winter as ice formation begins (freeze-up jams),
they may provide some protection during ice
those which form as a result of the breakup of ice
events as well.
covers (breakup jams), and those which contain
Ice events, however, present hazards that may
characteristics of both (combination jams). His-
not be adequately addressed using mitigation
torical ice records may not differentiate between
measures designed for open-water events only.
types of ice events, making it difficult to charac-
Consequently one major purpose of this study
terize them.
was to provide general guidance to facilitate ade-
Historical ice records for the Lower Platte, Loup
quate warning and response to ice-jam events.
and Elkhorn Rivers were obtained through a liter-
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