Restoring Wetlands in the Illinois River Floodplain

ISGS scientists are investigating the hydrology of a former Illinois River floodplain site to determine the best way to restore wetlands there. The parcel was recently bought by the Illinois Department of Transportation (IDOT) as part of their wetland mitigation program.

The 1,600-acre site, located at the confluence of the LaMoine and Illinois Rivers, was converted to farmland prior to the 1940s. Levees, drainage tiles, ditches, a surface-water pump station, and a lock and dam all combined to drain the site.

ISGS hydrologists are analyzing the site to determine the best strategy to restore some of the floodplain functions that are critical to the health of the river while also serving IDOT's needs by maximizing the acreage of restored wetland. By comparing historical and modern river stage data to levee heights and on-site topography, scientists determined that reintroducing the Illinois River to the site would inundate some of the existing wetlands. However, allowing the river to re-enter the floodplain would restore other previously drained wetlands on the site. The strategy would also improve water quality in the Illinois River by reducing sediment loads and nutrient levels and would re-create a backwater component of the riverine habitat that supported diverse plant and animal life in the past.

In 2002, spring flooding breached a levee, deeply inundating the site. Scouring, excessive sedimentation, and damage to the levees are being catalogued to determine the most appropriate wetland restoration plans. Historical stage records are also being examined to help predict the effects of the now-altered flood frequency relationship between the site and the river. Continued work by ISGS aims to provide IDOT with the means to make the best possible decisions for the site and the river.

ISGS scientists are cooperating with personnel from the Illinois Natural History Survey, University of Illinois-Springfield, and the Illinois Transportation Archaeological Research Program.

Updated 05/18/2011 SLD