In Reply Refer To:
Mail Stop 440

August 31, 2012


Subject: Announcing the Watershed Boundary Dataset as the Authoritative Data for Hydrologic Unit Boundaries

This memorandum is to announce that Watershed Boundary Dataset (WBD) is to be considered as the authoritative dataset for hydrologic unit boundaries for the nation. The WBD is an extension of the Hydrologic Unit Code dataset to a finer level of detail. Specifically, the WBD is more precisely delineated using larger scale source material, has a greater number of basin area designation categories based on six nested levels of hierarchy (2-, 4- 6-, 8-, 10, and 12-digit hydrologic units), and was developed through standards-based delineation procedures. Standardization of definitions and methodology provided consistency in the application of hydrologic unit boundaries across the nation minimizing interpretive variability. Researchers in USGS are strongly encouraged to use the WBD, or its derivatives, when modeling or describing a basin.

The WBD has undergone a certification process in accordance with the Federal standard and has been mandated by several Federal Agencies as the official hydrologic unit dataset for Federal environmental compliance and reporting. The WBD, along with the National Hydrography Dataset (NHD), is now being harmonized with both Canada and Mexico data through cooperative projects. When completed, the result will be continuous hydrographic data spanning the three nations’ international borders and providing an international framework for hydrographic applications and analysis.

The Federal Geographic Data Committee in its annual report describes the WBD as follows:

Both the NHD and the WBD are available from the USGS as part of The National Map located at:

The WBD continues to be available through the U.S. Department of Agriculture Data Gateway (with a 6 month refresh cycle), located at: A snapshot of the NHD will also be offered from this site. For more information, contact Jeff Simley or Karen Hanson


Katherine Lins //s// Katherine Lins
Chief, Office of Water Information


Seaber, P.R., Kapinos, F.P., and Knapp, G.L., 1987, Hydro­logic unit maps: U.S. Geological Survey Water-Supply Paper 2294, 63 p., accessed February 14, 2007, at

U.S. Geological Survey, 1994, 1:250,000-scale Hydrologic Units of the United States: Scale 1:250,000, accessed February 14, 2007, at

U.S. Geological Survey and U.S. Department of Agriculture, Natural Resources Conservation Service, 2011, Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD) (2d ed.): U.S. Geological Survey Techniques and Methods 11–A3, 62 p., accessed at