Abstract: This report documents the findings of a
but not documented. The results provide evidence
comprehensive survey that investigated the extent
that ice cover formation can trigger shifts in the
to which river ice influences channel bathymetry
channel thalweg location and can exacerbate ri-
along the Fort Peck reach of the Missouri River.
verbank erosion. The observations and data pro-
The Fort Peck reach stretches about 170 miles
vide insights for operating Fort Peck Reservoir, as
f r o m Fort Peck Dam, Montana, to Lake
well as for engineering activities in the Fort Peck
Sakakawea, North Dakota. The reach comprises
reach of the Missouri River. More generally, they
a channel of alluvial sinuous-braided morphology
indicate which riverbank stabilization structures
historically known for its shifting thalweg and ero-
likely work better in winter conditions, where river-
sion-prone banks. The survey, which entailed ex-
side water intakes might best be located, and the
tensive monitoring and detailed measurements of
effects of ice formation on local channel morphol-
channel bathymetry, ice conditions, and flow ve-
ogy at bridge crossings. The information also has
locity distribution, was conducted at five sites dur-
significance for dredging work. The conclusions
ing the winter of 1998-99. The observations and
are based on measurements made during the 1998-
data, though still preliminary and incomplete, indi-
99 winter season on the Fort Peck reach, when the
cate fundamental processes whereby river ice for-
hydraulic and ice conditions were unique during the
mation may influence channel bathymetry along
time of the measurements. Further work is needed
the Fort Peck reach, as well as other flow-regulat-
to confirm the processes and to understand the
ed, alluvial-channel rivers. Prior to the survey, the
short- and long-term interactions between the vari-
river ice processes had only been conceptualized
ables influencing the bankicesediment system.
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