TABLE 2.
Description of the 15 Hydrologic Metrics Used in This Study.
| Component | Metric Name | Definition | Expected Response to Urbanization | Units | Reference |
|---|---|---|---|---|---|
| Low Flow Pulse | Occurrence of daily average flows that are equal to or less than a threshold set at 50% of the long-term daily average flow rate | Summer low flows are more frequently interrupted by higher storm flows | |||
| Frequency | Low pulse count | Number of times each calendar year that discrete low flow pulses occurred | Increase | Count | Richter et al. (1996, 1997, 1998) |
| Duration | Low Pulse Duration | Annual average duration of low flow pulses during a calendar year | Decrease | Days | Richter et al. (1996, 1997, 1998) |
| Duration | Low Pulse Range | Range in days between the start of the first low flow pulse and the end of the last low flow pulse during a calendar year | Decrease | Days | This study |
| High Flow Pulse | Occurrence of daily average flows that are equal to or greater than a threshold set at twice (two times) the long-term daily average flow rate | High flow pulses occur more frequently and although flow magnitudes are higher, high pulse durations are shorter | |||
| Frequency | High Pulse Count | Number of days each water year that discrete high flow pulses occur | Increase | Count | Richter et al. (1996, 1997, 1998) |
| Duration | High Pulse Duration | Annual average duration of high flow pulses during a water year | Decrease | Days | Richter et al. (1996, 1997, 1998) |
| Duration | High Pulse Range | Range in days between the start of the first high flow pulse and the end of the last high flow pulse during a water year | Increase | Days | This study |
| Various | |||||
| Rate of Change | Fall Rate | The average rate of fall of all falling portions of the daily hydrograph during a calendar year | Increase | m3/s per day | Richter et al. (1996, 1997, 1998) |
| Rate of Change | Rise Rate | The average rate of rise of all rising portions of the daily hydrograph during a calendar year | Increase | m3/s per day | Richter et al. (1996, 1997, 1998) |
| Frequency | Fall Count | The number of days of declining daily average flows during a calendar year. A decline in flow is counted only when the rate of change is greater than −10% | Increase | Count | Richter et al. (1996, 1997) |
| Frequency | Rise Count | The number of days of increasing daily average flows during a calendar year. An increase in flow is counted only when the rate of change is greater than 10% | Increase | Count | Richter et al. (1996, 1997) |
| Frequency | Flow Reversals | The number of times that the flow rate changed from an increase to a decrease or vise versa during a water year. Flow changes of less than 2% are not considered | Increase | Count | Richter et al. (1998) |
| Flashiness | TQmean | The fraction of time during a water year that the daily average flow rate is greater than the annual average flow rate of that year | Decrease | Fraction of year | Konrad and Booth (2002), Konrad (2000) |
| Flashiness | R-B Index | Richards-Baker Flashiness Index – A dimensionless index of flow oscillations relative to total flow based on daily average discharge measured during a water year | Increase | Unitless | Baker et al. (2004) |
| Magnitude | Seven-day minimum | Centered seven-day moving average annual (calendar year) minimum flow | Decrease | m3/s | Richter et al. (1996, 1997, 1998) |
| Timing | Date of annual minimum | Julian day of the date of the minimum daily average flow during a calendar year | Earlier | Julian date | Clausen and Biggs (2000); Richter et al. (1996, 1997, 1998) |
Note: All metrics based on daily average flow.