The very local problem of jam failure also is a candidate for future research. The
vertical stress level throughout the thickness of a jam varies linearly when the jam
is at rest. This stress description is the basis for the determination of Kp and other
jam parameters. When water shear stress exists beneath the jam, however, the stress
levels within the jam change. No information exists about these stress levels and
whether they have an effect in setting up the initial instability within the jam. The
vertical description of jam failure, whether the jam initially fails at the bottom or at
the water-surface level, where stress is assumed to be the maximum, does not exist.
The highly dynamic nature of ice jamming precludes direct measurement of thick-
ness and ice velocity during formation, evolution, and failure. Equally difficult to
obtain are time-histories of water discharge and depth at several locations within a
reach experiencing jamming. A concerted effort needs to be undertaken to obtain a
complete set of field data for an ice jamming event, including water depths, water
velocities, ice thicknesses, and ice velocities at several locations. Another avenue of
model verification and validation would be a detailed physical model study of ice
jamming, going beyond the level of the flume experiments described in the Labora-
tory Experiments section. Such a data set will allow the verification and comparison
of unsteady ice models, such as the one presented in this study.
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