Hydrology and Hydraulics of the Illinois River

The Illinois River, one of the major tributaries to the Mississippi River in the Central United States, has a drainage area of 75,156 square kilometers (28,906 square miles) that covers portions of Illinois, Indiana, and Wisconsin. Except for about a 10,360 square kilometers (4,000 square miles) area in Indiana and Wisconsin, the Illinois River watershed is located within the state of Illinois. As a result of repeated leveling by glaciers, most of the Illinois River watershed is flat and covered with fine loess soil, making it one of the best agricultural regions in North America. More than 80 percent of the Illinois River basin is presently used for agricultural purposes. Most of the significant rivers in the state such as the DesPlaines, Fox, Kankakee, DuPage, Vermillion, Mackinaw, Spoon, Sangamon, and LaMoine Rivers all drain into the Illinois River. Restoration of the Illinois River will require proper understanding of the natural factors and how human-induced changes that control the hydrology of the watershed and the hydraulics of the river over time. This paper summarizes the historical changes that have affected the hydrology and hydraulics of the Illinois River basin and evaluate their influence on restoration efforts in the future.