Sediment management problems of backwater lakes Bhowmik, N. G. 1989. Sediment management problems of backwater lakes and alternative solutions. In Proceedings, Second Conference on the Management of the Illinois River System: The 1990s and Beyond, Peoria, Illinois, October 3- 4, 1989. Reprinted by U.S. Fish and Wildlife Service, Environmental Management Technical Center, Onalaska, Wisconsin, April 1993. EMTC 93-R014. 7 pp. (NTIS #PB94-116936) ABSTRACT Construction of locks and dams along the Illinois River, especially in the reach extending from Grafton to the Lake DePue area, has created a large number of backwater areas within the main floodplains of the river. These backwater areas are called backwater lakes, and they are subject to natural variations in water depths and sediment deposition. Moreover, over the last 100 years or so all the river basins in Illinois have been subjected to intense human activities and alterations. As a result of these natural and human interventions, the Illinois River valley has experienced a tremendous amount of sediment deposition in recent years. Many of the 53 or so backwater lakes along this river have lost 30% to 100% of their capacity to sediment deposition. Peoria Lake, a bottomland lake, has lost 68% of its 1903 capacity, and upper Peoria Lake will eventually attain the appearance of an incised river with broad and shallow wetlands on both sides. On the average, about 20.6 million tons of sediment is deposited annually over the entire valley, with a deposition rate of 0.81 to 2.1 inches per year. Recently implemented nonpoint source pollution control measures are showing their impacts on the receiving bodies of water through substantially lower concentrations of trace elements within the recently deposited sediment. Numerous alternative solutions can be considered for managing these backwater lakes, including constructing closing structures, periodic and selective dredging, using dredged materials to create artificial islands, diverting high flows, installing management practices on the watershed, and converting some of the backwater lakes to marsh and wetland habitats. A concerted effort, in which various physical, biological, and environmental factors are considered, is needed for the development of an acceptable management scenario for these backwater lakes. KEYWORDS backwater lakes, Illinois River, sedimentation, Peoria Lake, Upper Mississippi River System, management