Abstract: This file contains Hydrologic Unit (HU) polygon boundaries for the United States, Puerto Rico, and the U.S. Virgin Islands. The data is a seamless National representation of HU boundaries from 2 to 14 digits compiled from U.S. Geological Survey (USGS) National Hydrography Dataset (NHD) and U.S. Department of Agriculture (USDA) National Resources Conservation Service (NRCS) Watershed Boundary Dataset (WBD) sources. Purpose: This data is intended primarily for geographic display and analysis of regional and national data, and can also be used for illustration purposes at intermediate or small scales (1:250,000 to 1:2,000,000). See https://apps.nationalmap.gov/help/ for assistance with The National Map viewer, download client, services, or metadata.

Drainage areas (or watersheds) were calculated for each stream segment in the National Hydrography Dataset High Resolution Plus Beta (NHD HR Plus Beta) using non-end junction points and the provided hydrologically enforced Digital Elevation Model (DEM). The DEM was used to create a flow direction raster. The pour points used were determined from junction points at each stream intersection excluding stream ends (i.e. channel heads are not included). Watershed calculations were automated using the ArcGIS "watershed" tool and then edited manually for accuracy. In western San Diego County (non-desert) there were 39,980 drainage areas calculated. The percent impervious in each watershed was calculated using the National Land Cover Dataset 2019 Impervious surface.

This dataset is the digital hydrologic unit boundary layer for the 8-digit subwatershed boundaries for the conterminous United States. This dataset is intended to be used with the following two tabular dBase files: https://water.usgs.gov/lookup/getspatial?ds573_tillage_lu92e and https://water.usgs.gov/lookup/getspatial?ds573_tillage_lu01. The two tabular datasets contain the Tillage Practices in the Conterminous United States, 1989-2004---Datasets Aggregated by Watershed. This dataset and the two tabular datasets can be linked using the common attribute HUC8_N. Information about how the tabular data and geospatial data can be related are given in the data series report: https://pubs.usgs.gov/ds/ds573/ .The original dataset is the 12-digit Subwatershed boundaries (WBD_archive_17nov2009_9.2_file). The 12-digit boundaries were dissolved to 8-digit boundaries to be used with the two tabular .dbase data files containing the tillage practice data for the United States. ORIGINAL METADATA: This data set is a complete digital hydrologic unit boundary layer to the Subwatershed (12-digit) 6th 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.ncgc.nrcs.usda.gov/products/datasets/watershed/index.html . 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.

This dataset is the digital hydrologic unit boundary layer for the 8-digit subwatershed boundaries for the conterminous United States. This dataset is intended to be used with the following two tabular dBase files: https://water.usgs.gov/lookup/getspatial?ds573_tillage_lu92e and https://water.usgs.gov/lookup/getspatial?ds573_tillage_lu01. The two tabular datasets contain the Tillage Practices in the Conterminous United States, 1989-2004---Datasets Aggregated by Watershed. This dataset and the two tabular datasets can be linked using the common attribute HUC8_N. Information about how the tabular data and geospatial data can be related are given in the data series report: https://pubs.usgs.gov/ds/ds573/ .The original dataset is the 12-digit Subwatershed boundaries (WBD_archive_17nov2009_9.2_file). The 12-digit boundaries were dissolved to 8-digit boundaries to be used with the two tabular .dbase data files containing the tillage practice data for the United States. ORIGINAL METADATA: This data set is a complete digital hydrologic unit boundary layer to the Subwatershed (12-digit) 6th 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.ncgc.nrcs.usda.gov/products/datasets/watershed/index.html . 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 Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the "Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)" "Standard" (https://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications. For additional information on NHD, go to https://www.usgs.gov/national-hydrography.