SEDIMENTATION CORRELATED TO POOL-WIDE DRAWDOWN ON THE 
UPPER MISSISSIPPI RIVER

Jonathan W. Petersen and Corby Lewis
Army Corps of Engineers Centre, 190 East Fifth Street, St. Paul, Minnesota 55101-1638

Hydrodynamic and sedimentation models and monitoring have provided insight to the 
physical effects of a pool-wide drawdown in the Upper Mississippi River. The drawdown 
was completed in Pool 5 during the summer of 2005.  The effects of the drawdown on the 
main channel as well as backwaters, most notably Weaver Bottoms were determined.  
The Corps has completed a one-dimensional model of main channel sediment capacity in 
Pool 5, comparing normal water levels to drawdown levels.  Discharge measurements 
were completed during the drawdown and compared to normal years distributions.  A 
suspended sediment analysis and budget of Weaver Bottoms was done during the 
drawdown and compared to a similar study in 1993 & 1994.  

The one-dimensional sediment capacity analysis was completed with HEC-RAS, using 
the hydraulic design – sediment transport capacity function.  A calibrated model using 
flow split discharge measurements was used in conjunction with England-Hansen 
sediment transport functions to calculate sediment transport capacity in the main channel.  
The calculated sediment capacity compared reasonably to a sediment budget for pools 1 
through 10, however significantly more variation was obtained with the model.  Dredging 
and depositional areas were evaluated in detail.

Numerous discharge measurements on the main, secondary, and tertiary channels were 
completed during the drawdown and compared to previous measurements.  The 
drawdown altered flow patterns in all channels; results showed decreased flow in 
secondary and tertiary channels and increased flow in the main channel.  The average 
increase in main channel flow during the drawdown was 10%. 

A suspended sediment study was completed for Weaver Bottoms, with daily 
measurements collected at all major inlets and outlets to the area.  Analysis completed 
includes a suspended sediment budget, assessment of the relationship between wind, 
submerged aquatic vegetation, and total suspended solids, a comparison to 1993 & 1994 
data, and determining drawdown effects on sediment movement.

Keywords: sedimentology, Mississippi River, drawdown, backwaters, Pool 5