ECOHYDROLOGY OF THE ILLINOIS RIVER:  DEVELOPMENT  OF  CRITERIA  FOR
OPERATIONS OF THE LA GRANGE AND PEORIA LOCKS AND DAMS

Todd M. Koel 1, 2 and Richard E. Sparks 3, 4.
1 Minnesota Department of Natural Resources, Mississippi Monitoring Station, Lake 
City, MN 55041; 2 U.S. Geological Survey, Upper Midwest Environmental Sciences 
Center, La Crosse, WI 54603; 3 Water Resources Center, University of Illinois at 
Urbana-Champaign, Urbana, IL 61801; and 4 Illinois Natural History Survey, Long 
Term Resource Monitoring Program, Havana Field Station, 704 North Schrader 
Avenue, Havana, IL 62644.

The hydrologic regime of the Illinois River has been severely altered over the past 100 
years by many factors.  Locks and dams located at several locations along the river to 
allow commercial navigation have the ability to regulate water surface elevations and 
flow.  This study was initiated to relate changes in surface elevation to biotic 
productivity of the river, and to establish target criteria for operations of locks and 
dams.  Utilizing long-term records of daily river stage, we developed ecologically-
meaningful hydrological parameters for eight gage locations along the Illinois River. 
Variability in stage magnitudes, durations, frequencies, timings, and rates of change 
of pulse events were related to inter-annual variability of a long-term fisheries dataset 
from a survey beginning in 1957.  Reversals in surface elevation, maximum stage 
levels, and high pulse durations were the most important parameters influencing 
abundances of age-zero fishes in our annual collections.   Smallmouth buffalo 
(Ictiobus bubalus), white crappie (Pomoxis annularis), freshwater drum (Aplodinotus 
grunneins), and white bass (Morone chrysops) were most abundant in our samples 
during years which approximated the natural flow regime.  Of the 31 hydrologic 
parameters developed for the entire water year from an Illinois River gage site on La 
Grange Reach, only five post-diversion means were within established target criteria 
based on the historic, pre-diversion range of variation, from 1879 to 1899.  The 
highest degree of hydrologic alteration over the past 100 years was for minimum 
stage levels, low pulse count, rates of river rise and rates of river decline.  Operations 
of the La Grange and Peoria locks and dams should be modified so water level 
variability will approximate that of the late 1800s, when fish and wildlife resources 
were abundant on this great river.

Keywords:  large river fishes, hydrology, floodplain connectivity, water level 
variability, ecosystem management
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