Table 1. Summary of hydrologic parameters used in the IHA and RVA, and their characteristics.
| General Group | Regime Characteristics | Streamflow Parameters Used in the RVA |
Examples of Ecosystem Influences |
| 1. Magnitude of Monthly Discharge Conditions | Magnitude Timing | 1. Mean discharge for each calendar month |
* Habitat availability for aquatic organisms
* Soil moisture availability for plants * Availability of water for terrestrial animals * Availability of food/cover for fur-bearing mammals * Reliability of water supplies for terrestrial animals * Access by predators to nesting sites * Influences water temperature, oxygen levels, photosynthesis in water column |
| 2. Magnitude and Duration of Annual Extreme Discharge Conditions | Magnitude Duration |
1. Annual maxima one-day means
2. Annual minima one-day means 3. Annual minima 3-day means 4. Annual maxima 3-day means 5. Annual minima 7-day means 6. Annual maxima 7-day means 7. Annual minima 30-day means 8. Annual maxima 30-day means 9. Annual minima 90-day means 10 Annual maxima 90-day means 11 Number of zero-flow days 12 7-day minimum flow divided by mean flow for year (Abase flow @) |
* Balance of competitive, ruderal, and stress-tolerant organisms
* Creation of sites for plant colonization * Structuring of aquatic ecosystems by abiotic vs. biotic factors * Structuring of river channel morphology and physical habitat conditions * Soil moisture stress in plants * Dehydration in animals * Anaerobic stress in plants * Volume of nutrient exchanges between rivers and floodplains * Duration of stressful conditions such as low oxygen and concentrated chemicals in aquatic environments * Distribution of plant communities in lakes, ponds, floodplains * Duration of high flows for waste disposal, aeration of spawning beds in channel sediments |
| 3. Timing of Annual Extreme Discharge Conditions | Timing |
1. Julian date of each annual one-day maximum discharge
2. Julian date of each annual one-day minimum discharge |
* Compatibility with life cycles of organisms
* Predictability/avoidability of stress for organisms * Access to special habitats during reproduction or to avoid predation * Spawning cues for migratory fish * Evolution of life history strategies, behavioral mechanisms |
| 4. Frequency and Duration of High/Low Flow Pulses | Magnitude Frequency Duration |
1. # of high pulses each year
2. # of low pulses each year 3. mean duration of high pulses within each year 4. mean duration of low pulses within each year |
* Frequency and magnitude of soil moisture stress for plants
* Frequency and duration of anaerobic stress for plants * Availability of floodplain habitats for aquatic organisms * Nutrient and organic matter exchanges between river and floodplain * Soil mineral availability * Access for waterbirds to feeding, resting, reproduction sites * Influences bedload transport, channel sediment textures, and duration of substrate disturbance (high pulses) |
| 5. Rate/Frequency of Hydrograph Changes | Frequency Rate of change |
1. means of all positive differences between consecutive daily values
2. means of all negative differences between consecutive daily values 3. # of flow reversals |
* Drought stress on plants (falling levels)
* Entrapment of organisms on islands, floodplains (rising levels) * Desiccation stress on low-mobility streamedge (varial zone) organisms |