Sediment Budget and Trends in Sediment Delivery for the Last 30 Years in the Illinois River Basin

The Illinois River drains nearly half of the state. Many major streams in Illinois drain into it. The Illinois Waterway with its system of locks and dams links Chicago and the Great Lakes to the Mississippi River, and thereby to the Gulf of Mexico. This linkage has a significant transportation and commercial value for the state and the nation. In addition, with its numerous backwater lakes, wetlands, and floodplain forests, the Illinois River Valley provides a significant habitat for fisheries, waterfowl, birds, and other animals, making it an important ecological resource.The Illinois River’s environment has been subjected to many of the impacts associated with the develop-ments in the watershed, including waste discharges from urban areas, water-level control for navigation, and sediment and chemical inflow from agricultural lands. The water quality of the river was severely degraded for several decades prior to the 1970s when environmental regulations were enacted to control pollutant discharges. Since then the river water quality has been gradually improving. However, problems associated with erosion and sedimentation still persist and are recognized as the primary environmental problem in the Illinois River Valley (Illinois State Water Plan Task Force, 1987). The main sources of sedi-ment to the Illinois River Valley are watershed erosion, streambank erosion, and bluff erosion. The contri-bution of watershed erosion to the sedimentation problem in the Illinois River Valley can be quantified by analyzing the sediment yields of tributary streams that drain into the valley.The Illinois State Water Survey has been assessing the trends in sediment delivery to the Illinois River and the resulting sedimentation rates and patterns in the Illinois River Valley since the 1970’s. The results of the latest assessment of the sediment budget and trends in sediment delivery will be presented in this paper.