Bank erosion of the Illinois River

The Illinois River is a major tributary of the Mississippi River draining about 75,000 sq km of land in the States of Illinois, Indiana and Wisconsin. Most of the drainage area is contained within the State of Illinois. The river originates near Chicago, Illinois and after traveling about 500 km within the State of Illinois, it joins the Mississippi River near Alton, Illinois upstream of the City of St. Louis. The river has been altered over the years especially in 1939 after a series of Locks and Dams were constructed to facilitate the movement of river traffic. Two detailed attempts were made in the history of the river to document the bank erosion of this river. Both the research was conducted by the author with assistance from a number of colleagues and associates. The present research was completed to identify the erosion sites including their severity, probable causative factors and the development of a classification system. During this research, a team of engineers, geomorphologic experts and field professionals traveled the entire length of the river by boats extending several weeks. During this trip, a number of typical bank erosion sites were identified, bank material samples were collected, data on river cross-sectional profiles were collected, photographs were taken, and a field evaluation of the causative factor or factors were noted. Subsequently, all the field data were evaluated and bank erosion sites were classified. Based on this analysis, all the sites were classified into six separate classifications based on the probable causative factors of bank erosion, bank material composition, and the geometrical features of the banks. Bank erosion of any river occurs as a result of a variety of natural forces and human induced activities. The analysis for the Illinois River has shown that about 74% of the bank erosion sites were subjected to seepage flows. About 28% of the bank sections have shown the evidence of river traffic induced impacts. Other causative factors included eddy currents, disturbed flows due to exposed tree roots, surface drainage, and weathering due to rapid freezing and thawing cycle. This research will guide the future management activities of the Illinois River as far the river bank erosion process is concerned.