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 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.
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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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About the Prairie Research Institute: The Prairie Research
Institute (PRI) at the University of Illinois at
Urbana-Champaign provides objective expertise, data, and applied
research to aid decision making and provide solutions for
government, industry, and the people of Illinois. PRI is the
home of the state’s five scientific surveys: the Illinois
Natural History Survey, Illinois State Archaeological Survey,
Illinois State Geological Survey, Illinois State Water Survey,
and Illinois Sustainable Technology Center.
www.prairie.illinois.edu
[Lisa A. Sheppard]
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