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
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 |