Karaki and VanHoften (1974: 19) indicate that the sediment plume 

 of towboats, shown in infrared photographs, spreads across the main 

 channel and can be carried to backwater areas if there is a flow into 

 these areas from the main stream. Another statement supporting lateral 

 movement of resuspended sediments on the Illinois and Mississippi Rivers 

 is a conclusion by Johnson (1976: 124): 



It was found that lateral movement of sediments resus- 

 pended by tows and transported from the main channel to 

 shoreward areas , including potentially productive side 

 channel areas, does occur during normal pool conditions. 



Jackson turbidimeter readings of Lake Chautauqua, LaGrange Pool, 

 taken in 1977, indicate that suspended sediments are transported into 

 backwaters during high water (Table41 ). These findings indicate 

 that turbidity was greatest at a break in the levee at the southwest 

 shore and decreased gradually toward the middle of the lake and away 

 from the levee. 



It is the authors' opinion that when the river is flowing into 

 backwater lakes, passage of barge traffic will result in lateral transport 

 of resuspended sediment into backwater lakes, resulting in an increased 

 sedimentation rate. 



The single greatest physical effect of increased sedimentation in 

 the Illinois and Mississippi River valleys has been the acceleration 

 of filling in backwater areas. The Illinois State Water Survey has 

 found that backwater areas such as Meredosia in pool 26 are filling at 

 relatively rapid rates. Lake Meredosia in 72 years lost 46% of its 

 original storage capacity. The Water Survey calculated that the expec- 

 ted life of this lake is less than 100 years (Lee, Stall, and Butts, 

 1976: 7). 



Sedimentation has adversely affected marsh and aquatic plants by 

 creating a soft, false bottom and by filling shallow areas inhabited 

 by these plants. 



Our conclusions regarding the amount and effect of sedimentation 

 in the study area conflict substantially with those drawn by Simons et al. 



147 



