SURVEY OF RIVER ICE INFLUENCES ON CHANNEL
BATHYMETRY ALONG THE FORT PECK REACH OF
THE MISSOURI RIVER, WINTER 19981999
LEONARD J. ZABILANSKY, ROBERT ETTEMA, JAMES WUEBBEN, AND
NORBERT E. YANKIELUN
1
INTRODUCTION
It is well known that alluvial channel bathymetry adjusts in accordance with
prevailing conditions of water flow, alluvial sediment availability, and channel
bank conditions. Because river ice affects these conditions, it potentially influ-
ences alluvial channel morphology. It may do so over a range of scales in space
and time. The extent and full nature of river ice influences, however, have yet to
be determined. Some influences are reasonably well understood and some barely
recognized; few have been investigated rigorously. It is well known, for instance,
that an ice cover affects the vertical and lateral distributions of flow in a channel.
Less well known are how river ice influences the flow's capacity to entrain and
transport alluvial sediment and the geotechnical stability of channel banks flank-
ing the flow. To a large extent the influences likely are seasonal, coming and
going with the annual occurrence of winter weather. They also may have an
enduring impact, such as reducing riparian vegetation growth along a channel. In
overall terms, river ice influences on alluvial channel morphology are not well
known.
Numerous studies have focused on the channel morphology, flow, and sedi-
ment transport conditions along the Missouri River. Several studies have investi-
gated conditions of ice formation along the river. Only a few studies have been
conducted to determine the relationships between flow, channel conditions, and ice.
Objectives
This study comprises a comprehensive survey conducted with the primary
objective of determining if and how river ice influences channel bathymetry
along the Fort Peck reach of the Missouri River (Fig. 1). The river along this
reach is long known for its wandering thalweg and eroding riverbank propensi-
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