Cade, B.S. 2006. National Hydrologic Assessment Tool (NATHAT). U.S. Geological Survey.
The National Hydrologic Assessment Tool (NATHAT) is based on a hydrologic classification of streams by Poff (1996) involving 420 gaging stations across the contiguous United States (Figure 1). The Hydrologic Index Tool (HIT) is available for batch processing of multiple USGS gauge records to compute the 171 hydroecological indices for specified periods of record. If you have daily and peak (optional) streamflow data for a period of record, you can use NATHAT to
establish a hydrologic baseline (reference time period),
establish environmental flow standards, and
evaluate past and proposed hydrologic modifications.