National Hydrologic Assessment Tool (NATHAT)

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

1. establish a hydrologic baseline (reference time period),
2. establish environmental flow standards, and
3. evaluate past and proposed hydrologic modifications.

1. download and read
   • Poff, N.L. 1996. A hydrogeography of unregulated streams in the United States and an examination of scale-dependence in some hydrological descriptors. Freshwater Biology 36:71-91.
   • Olden, J.D., and N.L. Poff. 2003. Redundancy and the choice of hydrologic indices for characterizing streamflow regimes. River Research and Applications 19:101-121.
2. download and read the Users’ Manual for the Hydroecological Integrity Assessment Process Software,
3. download the NATHAT software (version 3.4)
4. download the HIT software (version 1.4)