Champaign, Ill. - Although water quality in the Illinois River has improved since regulations were enacted to clean up pollution, an ongoing–yet pressing–issue is too much sediment delivered into the Illinois River valley and its connected backwater lakes.

Researchers at the Prairie Research Institute's Illinois State Water Survey (ISWS) have computed a sediment budget over 35 years to determine the amount of sediment coming into the river valley and the amount going out to the Mississippi River. Research shows that an average 12.9 million tons of sediment was delivered annually to the Illinois River valley in 1981 to 2015, and only 5.2 million tons has been removed from the area, according to Laura Keefer, fluvial geomorphologist at ISWS.

Therefore, on average, an estimated 7.8 million tons of sediment from tributary streams, or 60 percent, was deposited annually. The total deposition of sediment may be higher as a result of erosion from river banks and bluffs along the main stem of the Illinois River.

The intensity of water flowing across the land and into rivers and lakes is an especially important factor in sediment deposition, Keefer said.

“Fast flowing water is hungry water; it has teeth,” said Keefer, describing the way that water flows from the land and stream channels, eroding sediment and depositing it into river valleys and bottoms.

Researchers are especially concerned about the main river channel and backwater lakes of the river. Sediment deposition has already filled in several backwater lakes and nearly filled others, with economic ramifications for river towns and habitat degradation. This string of lakes plays a major role in the Mississippi flyway, where migrating waterfowl stop to rest on their journeys. Sediment also disrupts bird and animal habitats and fisheries.

Another significant issue is the economic impact of barge traffic along the Illinois River. The U.S. Army Corps of Engineers must have the resources to remove sediment to keep navigation channels clear for barge freight and boating.

The study report, The Sediment Budget of the Illinois River: 1981-2015, is available on the ISWS website at http://www.isws.illinois.edu/pubs/pubdetail.asp?CallNumber=ISWS+RI%2D122

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Source: Laura Keefer - (217) 333-3468, lkeefer@illinois.edu

Editor: Lisa Sheppard (217) 244-7270, sheppard@illinois.edu