Creek. The jam profiles are up to several feet higher
as the index of severity. His method assumes that
than the open-water and stable-ice-cover profiles
this incremental increase in stage is a function of
as expected, but in some locations the breakup
the ice thickness, the depth of snow, the rate of
profile approaches the open-water profile because
rise of stage prior to ice jamming, the accumulat-
there is no ice. Better analysis of Platte River ice
ed freezing degree-days during the ice breakup
jams could be accomplished with more detailed
or simply the existence of subfreezing tempera-
geometry and field data relating to ice volume
tures, the character of the ice, the difference in
and thickness.
time between ice breakup on the main stem and
significant tributaries, and the ratio of total heat
input per unit surface area in the ice-jamming
region and the total heat input per unit surface
PREDICTIVE MODEL FOR
area in the flood-formation region.
ICE JAM OCCURRENCE
Because detailed, long-term data for many of
these parameters may be difficult to obtain, Shulia-
Past methods
The ability to forecast the occurrence and severi-
kovskii presented a simplified application of the
ty of an ice jam would provide early warning, which
prediction technique. For the case where no sig-
could decrease damages due to ice jams within
nificant tributaries are present, the time of break-
the study area. As a result the Interagency Hazard
up on tributaries vs. the main stem may be ne-
Mitigation Team requested the development of
glected. If the ice-jam region is either coincident
some type of model that could be used to forecast
with or very similar to the source of runoff in
ice jams in the study area. While models have been
terms of heat input, the heat terms may be ne-
developed for use in predicting open-water flood
glected. Ice thickness may be estimated using
events, there are few existing models that can be
AFDD. The term describing the character of the
used to predict the occurrence and severity of
ice is neglected if the thickness and condition of
breakup ice jams. There have been a number of
the ice cover contributing to the jam are relatively
attempts to develop a prediction scheme for ice
uniform. Finally the temperature statistic of inter-
breakup, the prelude to breakup ice-jam formation.
est may be modified to more closely reflect condi-
For the most part these methods address the for-
tions at the prediction site.
mation of cracks in the ice as a result of increases in
Zhukova (1979) discussed some important
stage over the freeze-up stage (see, for example,
parameters to consider in developing a method
Beltaos 1990). The cracks, combined with increased
to predict the occurrence of an ice jam. Working
stage and discharge, result in ice-cover breakup
with long-term stage and discharge data for sev-
and movement. The thickness and deterioration
eral river basins, she developed a method to pre-
of the ice and the rate of the stage increase are
dict stages due to ice jams in particular river reach-
often considered, as well as river geometry and
es. This method utilizes an observed relationship
meteorological and hydrological conditions.
between the long-term average normalized in-
Unfortunately, while ice-cover breakup is nec-
crease in stage due to ice jams and the ratio be-
essary for breakup ice-jam formation, the predic-
tween long-term average ice-jam stages and open-
tion of breakup alone is not sufficient to predict
water stages for the basins examined.
the occurrence and severity of breakup ice jams.
The prediction method relies on determining
The few methods to predict breakup ice-jam for-
the increase in stage due to ice over the long-term
mation that presently exist are based on probabi-
average low-flow stage. The method for deter-
listic or statistical analyses of past ice events and
mining the long-term average low-flow stage was
the parameters associated with ice jams at a partic-
not specified. Zhukova assumed that the total in-
ular location. Shuliakovskii (1963) presented two
crease in stage due to an ice jam is the sum of the
cases in which the probability of a breakup ice
incremental increase in stage due to the ice and
jam occurring can be predicted based on a statisti-
the increase in stage attributable to the jam dis-
cal analysis of historical events. The predictions
charge alone. For comparison between different
are based on the maximum stable ice stage in one
sites, the incremental stage increase due to ice is
case and on the rise in water stage and the air tem-
normalized by the total increase in stage due to
perature during jam formation in the second case.
an ice jam, and the stage increase due to discharge
Shuliakovskii also presented a technique for
during an ice jam is normalized by the stage in-
forecasting the severity of a breakup ice jam using
crease due to the maximum open-water discharge.
the incremental increase in stage due to an ice jam
Once these parameters are computed, long-
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