Sediment apparently went into storage, either in the channel or the flood plain, upstream from St. Louis, Missouri, because the total suspended sediment transported by the Mississippi River past St. Louis was 22 million metric tons less than that transported past the two upstream sediment stations--below Grafton, Illinois, and at Hermann, Missouri. The storage of sediment was partly verified by the massive amounts of newly deposited sediments on the flood plains.

A nonhomogenous mixture of water is present at St. Louis, which is 24 kilometers downstream from the normal junction of the Missouri and the Mississippi Rivers. During the 1993 flood, the suspended-sediment concentration varied from one shoreline to the other by a factor of nearly five. Aerial photography taken on July 25 indicates the river became well mixed 88 kilometers downstream from the normal junction of the two rivers. Several days before and after July 25, the junction of the two rivers was 32 kilometers upstream from the normal junction.

The dynamics of sediment transport and movement were exemplified by 4 meters of channel-bed scour from July 12 through July 20 at the Mississippi River at Chester, Illinois. The channel-bed changes generally followed a pattern of scouring during the flood rise followed by channel-bed aggradation during the recession.