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Table 1 Hydrology variables that were significantly altered (P < 0.05) from Indicators of Hydrologic Alteration analysis (Richter et al. 1996) using daily discharge from the Valley City, Illinois, USGS gaging station on the lower Illinois River. We used discharge data from 1939 to 2015 to create hydrology variables, which were then regressed with year to detect significantly altered variables

From: Conservation potential of North American large rivers: the Wabash River compared with the Ohio and Illinois rivers

IHA group Correlation r P value
Group 1: monthly magnitude
 December 0.27 0.025
 June 0.28 0.025
 September 0.25 0.025
Group 2: magnitude duration of annual extremes
 3-day minimum 0.28 0.025
 7-day minimum 0.30 0.01
 30-day minimum 0.26 0.025
 30-day maximum 0.25 0.025
 90-day maximum 0.28 0.025
Group 4: frequency and duration of high and low pulses
 High pulse duration 0.41 0.001
Group 5: rate and frequency of change in conditions
 Rise rate 0.37 0.001
 Fall rate − 0.44 0.001