Hydrologic Variability Data:

Background Information

The data presented here is an introduction to some statistical measures which may be useful in quantitative analyses of the role of hydrologic variability in water quality assessment. Investigating the effects of hydrologic regime on ecological communities has demonstrated correlations between measures of hydrologic variability and various stream quality characteristics.

Along with traditional parameters of monthly means and various periodic maxima and minima, additional parameters describing magnitude, duration, frequency, and timing of annual extreme conditions and high and low pulses are included (Richter and others, 1996). The database also includes parameters developed by Colwell (1974) for characterizing the predictability of phenomena in nature which recur on a periodic basis. The Nature Conservancy has developed a software application which calculates hydrologic regime parameters to be used in assessing stream impacts such as dams or major water diversions (Nature Conservancy and Smythe, 1997). This software, Indicators of Hydrologic Alteration (IHA), was used to calculate the desired hydrologic variability statistics.

You may read more about The Nature Conservancy's Indicators of Hydrologic Alteration by going to the IHA web site at http://www.freshwaters.org/tools. Note: this is a non-USGS web link.