Table 1. Summary of hydrologic attributes used in the Indicators of Hydrologic Alteration and their characteristics (modified from Richter and others, 1996)
[IHA, Indicators of Hydrologic Alteration; *, attribute used in this report]
IHA
statistics group |
Regime characteristics |
Hydrologic attributes |
Group 1: Magnitude of monthly water conditions
|
Magnitude Timing |
* Mean for each calendar month (median in this application)
|
| Group 2: Magnitude and duration of annual extreme water conditions
|
Magnitude Duration
|
* Annual minimums of 1-day means * Annual maximums of 1-day means * Annual minimums of 3-day means * Annual maximums of 3-day means * Annual minimums of 7-day means * Annual maximums of 7-day means * Annual minimums of 30-day means * Annual maximums of 30-day means * Annual minimums of 90-day means * Annual maximums of 90-day means |
Group 3: Timing of annual extreme water conditions
|
Timing
|
Julian date of each annual 1-day maximum Julian date of each annual 1-day minimum |
Group 4: Frequency and duration of high- and low-flow pulses
|
Magnitude Frequency Duration
|
* Number of high-flow pulses each year * Number of low-flow pulses each year Mean duration of high-flow pulses in each year Mean duration of low-flow pulses in each year |
Group 5: Rate and frequency of water-condition changes
|
Frequency Rate of change
|
Means of all positive differences between consecutive daily means Means of all negative differences between consecutive daily means Number of rises Number of falls |