Net rates of sediment accumulation were measured as changes in
bed elevation along selected backwater transects during several
time intervals between 1989 and 1996. The average net rate of
accumulation was found to be lower than previously reported for
the Upper Mississippi River. Mean rates (in centimeters per
year) the transects surveyed were 0.29 for Pool 4, 0.12 for Pool
8, and 0.80 for Pool 13. Rates were highly variable among
transects with standard deviations (in centimeters per year) of
1.14 in Pool 4, 0.55 in Pool 8, and 1.45 in Pool 13. All three
study pools had transects with net erosion and transects with net
sedimentation. Accumulation rates were variable along transects
as well, with most transects crossing areas of both erosion and
sedimentation. Bed elevation changes were also variable
temporally, particularly related to the Flood of 1993. High
discharge during 1993 resulted in more accumulation in shallow
areas and more erosion in deeper areas than occurred during
periods before and after the flood. However, sedimentation
patterns during 1993 were varied among transects. The findings
of these surveys illustrate the need to account for spatial and
temporal variability when evaluating and projecting sedimentation
problems in the Upper Mississippi River.
