ning in early January 1994. Using the adjusted
tant to determine as those that do, so observa-
discharges would result in ice-event predictions
tions should be made carefully even during win-
for 19 February and 2 March 1994. Although no
ters in which jamming is unlikely. Observations
ice jams formed at North Bend during 1994, an ice
of ice breakup and transport are particularly im-
jam formed on the Platte River downstream of
portant, whether or not a jam forms. The charac-
the confluence with the Elkhorn River on 20 Feb-
teristics of a jam which does not result in flooding
ruary 1994. Jams also reportedly formed on the
should be documented as completely as those of
Platte River at Schuyler and upstream from High-
a jam which does cause damaging floods.
way 64 on 5 March 1994.
Primarily because of safety constraints, the field
Using the prediction criteria to predict ice jams
data collection portion of the program is to be
in the study area during 1994 was successful; how-
limited to visual observations and measure-
ever, the experience underscored the importance
ments that can be made on shore or from the air.
of obtaining and forecasting real-time ice-affected
The USGS, the Corps of Engineers, the Papio
discharge. Before the model can be applied with
Missouri River Natural Resources District (NRD)
any confidence, a reliable method to adjust provi-
and CRREL have personnel trained in making ice
sional discharges on a nearly real-time basis must
measurements. These are the only persons who
be developed. CRREL personnel are continuing
should attempt to make any measurements from
to develop a method to convert the provisional
the surface of the ice. Ice measurements should
ice-affected discharges into actual discharges for
never be made alone. Ice observers should be
use in the model.
aware of the possible safety hazards that are asso-
ciated with data collection and should both mini-
mize their exposure to these hazards and be pre-
pared to deal with any hazards that might occur.
DATA COLLECTION
Ice-data-collection efforts may have to be sus-
PROGRAM DESIGN
pended during particularly hazardous weather
The primary objective of an ice-data collec-
or flooding conditions, so it is best to plan alter-
tion program in the Lower Platte River basin is
natives if it is not possible to obtain data using the
to develop information useful in developing
ideal method. Other constraints affecting the type
advance or emergency response measures to ice
and quantity of data collected are budgetary
jams. The secondary objective is to collect fu-
limitations, time (e.g. events may occur rapidly),
ture data for input into the predictive model.
large geographic area and difficulty of access.
The data collection program design for the Low-
Representatives from the Omaha District of-
er Platte River basin is based on the guidelines
fice of the Corps of Engineers, CRREL, NWS
presented in White and Zufelt (1994). Table 15
(Omaha), USGS (Lincoln), Nebraska Natural Re-
lists the types of data that should be obtained to
sources Commission (NRC) and Nebraska Civil
meet the objectives of the data collection pro-
Defense were involved in creating a network of
gram. They may be categorized as either (1) his-
observers to make ice observations in the study
torical, or background, data or (2) physical data
area. In January 1994, CRREL personnel present-
that must be collected in the field. Historical
ed a two-day workshop to the observers and oth-
data collection performed to date and the anal-
ers involved in ice-jam detection or response. The
ysis of those data have been discussed in previ-
workshop presented information on ice charac-
ous sections. Any additional historical data re-
teristics, river and ice hydraulics, mitigation op-
vealed during the course of the ice data
tions and data collection.
collection program should be added to the da-
The observation form used by the observers,
tabase. Collection of field data, described in
the Nebraska Ice Report, is shown in Figure 17.
more detail below, may be categorized in chro-
The form was developed mainly with input from
nological order: freeze-up conditions, ice cover
the NRC, CRREL, Corps of Engineers and Civil
characteristics, breakup details, and ice-jam for-
Defense. Ice information collected using the Ice
mation, progression and release.
Report is incorporated into the NRC database and
Ice observations over a number of years will
is available for use by the Nebraska Civil De-
be necessary to refine the predictive ice-jam mod-
fense, Corps of Engineers, NWS and others. In
el. Ice observations will also be a key part of an
addition, the USGS forwards information on ice
ice-jam detection and warning system. The condi-
thickness measurements, which are also included
tions which do not lead to jamming are as impor-
in the database.
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