William C. Bogner

Hydrologic and Hydraulic Considerations for the Ecological Restoration of the Emiquon Along the Illinois River

The Nature Conservancy (TNC) has initiated a major ecological restoration project along the Illinois River to restore one of the largest levee and drainage districts that has been drained and farmed since 1924. The Thompson Lake Drainage and Levee District, located just upstream of the junction of the Spoon River with the Illinois River, was formed in the early 1920s by draining and leveeing a large floodplain area that included Thompson and Flag Lakes and diverse aquatic and terrestrial habitats that supported a wide variety of fish and wildlife. The restoration area known as the Emiquon is one of the largest floodplain restoration projects in the United States. The goal of the restoration effort is to restore ecological processes and habitats that could sustain the native aquatic and terrestrial species once found in the region prior to disturbance of the area. One of the key elements in the restoration effort is the proper understanding of the hydrology, hydraulics, and sediment transport processes in the Illinois River near the Emiquon area from a historical perspective, under existing conditions, and also for different management scenarios. Prior to making changes in the management of the area, TNC wisely initiated scientific investigations and analyses to guide the restoration effort. As part of this effort, the Illinois State Water Survey (ISWS) has collected hydrologic data and developed hydrologic and hydraulic models to assess existing conditions and evaluate different management alternatives that could be used during the restoration. This paper summarizes the results of those investigations.