The Geomorphic Network and Analysis Toolbox (GNAT) is a set of ArcGIS geoprocessing scripts used to generate geomorphic attributes for a spatially-explicit stream network dataset, and is designed specifically to work with the USGS National Hydrography Dataset (NHD). GNAT is written in Python as an ArcGIS Python Toolbox for ArcGIS version 10.4 or higher. GNAT partially relies on third-party libraries, including GDAL and the NetworkX Python library.

GNAT was originally developed to support the geomorphic attribute analysis and modeling efforts of the Integrated Status and Effectiveness Monitoring Program (ISEMP) and Columbia Habitat Monitoring Program (CHaMP). However, the tools found within GNAT are flexible enough to be used in a wide variety of data processing and analysis efforts revolving around stream networks, such as:

  • Stream network preparation
  • Attribute management
  • Segmentation of stream networks
  • Modeling geomorphic attributes


GNAT is actively developed and maintained by South Fork Research, Inc.

Please submit bug reports here.