(1975: 93-96). The conclusions differ because: (1) Simons et al. 

 studied the movement of sand only, and (2) they studied sedimentation 

 in the main channel only, not backwater areas which are the most im- 

 portant to fish and wildlife. 



In the Simons study, they limited sediment transport to sand 

 transport capacity (Simons et al. , 1975: 26). They concluded that 

 an increase of 3 percent occurred between 1929 and 1973 (Simons et al. , 

 1975: 77). Our observations indicate that in backwater areas the 

 deposition of silt rather than sand is the major constituent of 

 sediment in the Mississippi and Illinois River valleys. Furthermore, 

 turbidity of the water is the result of fine silt particles (Dorris, 

 Copeland, and Laver, 1954: 84), whereas sand, which is a larger, heavier 

 particle, is only suspended by fast-moving water. 



Simons' conclusion as to the amount of sedimentation was derived 

 from riverbed elevation changes only in the deepest 1,000-foot sec- 

 tion of the channel (Simons, 1975: 62). These areas are subject to 

 currents caused by towboats. In our studies on Peoria Lake in the 

 middle Illinois valley, there are areas where the river channel is 

 now deeper than in 1903 and adjacent areas, 100 feet from the channel, 

 have filled in dramatically. As one moves from the main channel to 

 lateral backwaters, the current diminishes, and the silt load is dropped. 

 The backwater areas, where the greatest amount of sedimentation oc- 

 curs, are also the most important areas for fish and wildlife. In 

 these areas submerged aquatic and marsh plants, which provide food and 

 habitat for fish and wildlife, have been reduced to mere remnants of 

 what they once were (see aquatic vegetation section; Bellrose et al. , 

 1976: C-19-C-46). 



Simons' conclusion that "50 years from now the river scene in the 

 study reach will be essentially as it is today" does not take into 

 account these factors. Although the river channel may remain stable, 

 the backwater areas are undergoing an accelerated rate of change. Suc- 

 cession has been increased to such an extent that changes that would 

 normally take thousands of years are being completed in less than 150 



149 



