Effects of Tow Traffic on the Resuspension of Sediments and on Dissolved Oxygen Concentrations in the Illinois and Upper Mississippi Rivers under Normal Pool Conditions
ARMY ENGINEER WATERWAYS EXPERIMENT STATION VICKSBURG MS VICKSBURG
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This study was conducted to determine the effects of single and multiple tow traffic on the resuspension of riverbed sediments and on dissolved oxygen concentrations at several locations on the Illinois and Upper Mississippi Rivers during normal pool conditions. In total, 19 separate tows were monitored on the Mississippi River and 21 tows on the Illinois River at locations chosen to correspond to upper, middle, and lower river reaches. Composite water-column samples were collected simultaneously at each sampling station at selected time intervals. Current velocity profiles, water depth, water temperature, and river stage were also measured. Dissolved oxygen measurements were made in situ at surface, mid-depth, and near-bottom strata in the main channel only. These analyses indicated that tow traffic on the Illinois and Upper Mississippi Rivers during normal pool conditions does contribute to existing levels of suspended sediment measured as both suspended solids and turbidity, and, furthermore, that sediments resuspended from the main channel do move laterally to shoreward areas, including potentially productive side channel areas. Based on the relative responses of suspended solids concentrations and turbidity levels following the passage of tow traffic on both the Illinois and Upper Mississippi Rivers, the Illinois River appears to be more susceptible to tow traffic effects than the Mississippi River. It was also shown that in most cases tow traffic did not reduce dissolved oxygen concentrations in the water column of the main channel of either river.