Description: This data set is a complete digital hydrologic unit boundary layer of the Subbasin (8-digit) 4th level for the entire United States. This data set consists of geo-referenced digital data and associated attributes created in accordance with the "Federal Guidelines, Requirements, and Procedures for the National Watershed Boundary Dataset; Chapter 3 of Section A, Federal Standards, Book 11, Collection and Delineation of Spatial Data; Techniques and Methods 11-A3" (04/01/2009). http://www.nrcs.usda.gov/wps/portal/nrcs/detail/national/water/watersheds/?cid=nrcs143_021630 . Polygons are attributed with hydrologic unit codes for 4th level sub-basins, 5th level watersheds, 6th level subwatersheds, name, size, downstream hydrologic unit, type of watershed, non-contributing areas and flow modification. The data is currently updated through the USGS National Hydrography Dataset (NHD) Program and replicated to NRCS twice per year.
Copyright Text: Funding and support for the Watershed Boundary Dataset (WBD) were provided by the Natural Resources Conservation Service, the Environmental Protection Agency, and the United States Geological Survey. Representatives from the U.S. Geological Survey and Environmental Protection Agency contributed a substantial amount of time and salary towards quality review and updating of the dataset in order to meet the Federal Standards for Delineation of Hydrologic Unit Boundaries.