Skip to Main Content U.S. Department of Energy
About PNNL
printer icon

Index of Hydrologic Alteration (IHA)


Tool Website:


The Indicators of Hydrologic Alteration (IHA) is a software program that provides useful information for those trying to understand the hydrologic impacts of human activities or trying to develop environmental flow recommendations for water managers. The software was developed to facilitate hydrologic analysis in an ecologically-meaningful manner. The program assesses many ecologically-relevant statistics derived from daily hydrologic data, including calculating the timing and maximum flow of each year's largest flood or lowest flows, and the mean and variance of these values over some period of time. Comparative analysis can then help statistically describe how these patterns have changed for a particular river or lake, due to abrupt impacts such as dam construction, or more gradual trends associated with land- and water-use changes.

Geographic Location

Not region specific


Measured or synthesized stream flow records


Many (67) ecologically-relevant statistics derived from daily hydrologic data

Linkage to Other Models

Level of Effort

Low. Software set up to be user friendly to import hydrology information and produce flow statistics.

Basin Scale Opportunity Assesment