Upper Mississippi River Restoration Program

Long Term Resource Monitoring

Backwater sedimentation rates in Pools 4, 8, and 13

Changes in bed elevation caused by sedimentation can have significant effects on aquatic and terrestrial components of a river. Managers predict that future changes in water depth will have dramatic effects on the backwaters of the Upper Mississippi River System (UMRS).

The Upper Midwest Environmental Sciences Center, through funding from the Long Term Resource Monitoring Program, has been estimating the net sedimentation rate in backwaters along two sets of established transects. Transects were established in Pools 4, 8, 13, and La Grange Pool in 1989 in a nonrandom fashion. To provide unbiased estimates, additional transects were randomly selected in a stratified manner in Pools 4, 8, and 13 in 1996.

The estimates are obtained by precise survey of the bed elevation along each transect. Temporary vertical and horizontal benchmarks were set to obtain relative water surface elevations and align the transect. Along aquatic portions of the transects, surveys are conducted over the ice by taping distances and measuring depths with a sounding pole. Nearshore and bank surveys are conducted during open water conditions using similar methods.

The present study design provides estimates of net sedimentation for backwaters as a whole, as well as for the three backwater types used in the stratified design. In addition, annual variability in rates and spatial variability of rates may be used to suggest dominant processes that control sedimentation rates.

Project was completed in September 2001.

Principal Investigator: Jim Rogala