The suspended sediment budget for Pool 13 of the Mississippi River and La Grange Pool of the Illinois River was examined over a 3-yr period (October 1995 through September 1997). Pool 13 output was between 3.07 and 3.64 million t (metric tons) of suspended sediment annually during the study period. Loads to Pool 13 were dominated by those delivered by the Mississippi River (76%, 74%, and 66% in the 1995, 1996, and 1997 water years, respectively). Pool 13 exhibited sediment export (output greater than input) in 1995, a balance in 1996, and marked sediment trapping (output less than input) in 1997. Within the three study years, Pool 13 received its highest water and sediment loads during spring (March through May) and this period was marked by sediment export. Suspended sediment loads were trapped during the remainder of the year. La Grange Pool output was between 3.71 and 5.04 million t of suspended sediment annually during the 1995-97 water years. The Illinois River accounted for less than 50% of the suspended sediment load to the pool (19%, 25%, and 45% in the 1995, 1996, and 1997 water years, respectively. La Grange Pool exhibited considerable sediment trapping in 1995 whereas the 1996 and 1997 water years were much closer to a balance wherein output was within 5% of input. Generally, La Grange Pool received its largest water and sediment loads during the late spring—early summer period (April through June), but in 1997 the late winter loads predominated. In all years, La Grange Pool trapped the sediments during these high discharge, high loading periods and exported suspended sediments for the remainder of the year. The distinct differences in the manner in which these pools process suspended sediment loads may be related to the considerable differences between the morphometry of these pools.
