Rates of sedimentation along backwater transects Rogala, J. T., and P. J. Boma. 1996. Rates of sedimentation along selected backwater transects in Pools 4, 8, and 13 of the Upper Mississippi River. U.S. Geological Survey, Environmental Management Technical Center, Onalaska, Wisconsin, October 1996. LTRMP 96-T005. 24 pp. (NTIS #PB97-122105) ABSTRACT 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. KEYWORDS backwaters, bed elevation, erosion, Mississippi River, sediment transport, sedimentation