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.

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.

Regional regression equations were calculated in Puerto Rico with generalized least squares techniques to estimate flood frequency statistics at ungaged locations using drainage area as the only explanatory variable. The island was divided into 2 regions to minimize residuals. The region division that resulted in lower and more balanced residuals runs primarily north-south near the center of the island, mostly along an 8-digit hydrologic unit code (HUC8) boundary. The division line runs through a HUC8 polygon on the southern end of the island, but care was taken to include entire watersheds and consideration was given where hydrologic and physiographic properties differed. This data release includes geographic information system files that define the polygons for both regions.

Regional regression equations were calculated in Puerto Rico with generalized least squares techniques to estimate flood frequency statistics at ungaged locations using drainage area as the only explanatory variable. The island was divided into 2 regions to minimize residuals. The region division that resulted in lower and more balanced residuals runs primarily north-south near the center of the island, mostly along an 8-digit hydrologic unit code (HUC8) boundary. The division line runs through a HUC8 polygon on the southern end of the island, but care was taken to include entire watersheds and consideration was given where hydrologic and physiographic properties differed. This data release includes geographic information system files that define the polygons for both regions.

This data set is a complete digital hydrologic unit boundary layer to the Subwatershed (12-digit) 6th level for the State of New Mexico. This data set consists of geo-referenced digital data and associated attributes created in accordance with the "FGDC Proposal, Version 1.0 - Federal Standards For Delineation of Hydrologic Unit Boundaries 3/01/02"(http://www.ftw.nrcs.usda.gov/huc_data.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. Arcs are attributed with the highest hydrologic unit code for each watershed, linesource and a metadata reference file.

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.

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.

This subset of the USGS Water Boundary Dataset contains the polygons of the 50 8-digit Hydrologic Units that comprise the greater Central Valley study site. The Watershed Boundary Dataset is a comprehensive set of digital spatial data that represents the surface drainages areas of the United States. The information included with the features includes a feature date, a unique common identifier, name, the feature length or area, and other characteristics. Names and their identifiers are assigned from the Geographic Names Information System. The data also contains relations that encode metadata. The names and definitions of all these feature attributes are in the Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD). The document is available online at https://pubs.usgs.gov/tm/11/a3/

In 2012, catchments were generated in the Delaware River Basin for 8-digit HUCs in the areas underlain by the Marcellus Shale (all of 02040101, 02040102, 02040103, 02040104; and headwater areas of 02040106 and 02040203) based on the National Hydrography Dataset (NHD) Strahler first- and second-order streams. There were areas that did not have a catchment generated so another methodology needed to be used in an attempt to fill in the 'gap areas'. A 900-cell, flow accumulation raster generated for the Pennsylvania StreamStats application was used as a surrogate stream layer with the same Strahler ordering system applied to help fill in the 'gap areas'. Points were manually placed at the downstream end of the Strahler Order 1 and 2 reaches using the surrogate streams as a guide. This manual point placement is different from the automated method used to develop the catchments generated from the NHD flowlines. The manual placement of the catchment pour points does not include a point downstream of a confluence, therefore, not as many catchments are generated in the 'gap-area' processing. The naming convention of directories housing the geospatial datasets is based on 8-digit Hydrologic Unit Code (HUC) designations. Directories 02040101 through 02040106 correspond to HUCs in the Upper Delaware Basin and directories 02040201 through 02040207 correspond to HUCs in the lower Delaware Basin. The directories and corresponding descriptions are: 02040101 - Upper Delaware. NY, PA; 02040102 – East Branch Delaware. NY; 02040103 – Lackawaxen. PA; 02040104 – Middle Delaware-Mongaup-Brodhead. NJ, NY, PA; 02040105 – Middle Delaware-Musconetcong. NJ, PA; 02040106 – Lehigh. PA; 02040201 – Crosswicks-Neshaminy. NJ, PA; 02040202 – Lower Delaware. NJ, PA; 02040203 – Schuylkill. PA; 02040204 – Delaware Bay. DE, NJ; 02040205 – Brandywine-Christina. DE, MD; 02040206 – Cohansey-Maurice. NJ; 02040207 – Broadkill-Smyrna. DE. The naming convention for shapefiles is based on the following: 1) 8-digit HUC designation 2) str1_ (Strahler stream order 1) or str2_ (Strahler stream order 2) _mgp (manual gap dataset using interactive processing) 3) _new (new dataset using automated processing) 4) 18 (shapefile projected into Universal Transverse Mercator (UTM), Zone 18, North American Datum (NAD) 1983, projection). The following four names are examples: 02040101str1_mgp18; 02040103str2_mgp18; 02040206str1_new18; 2040207str2_new18. The two processing times are “new” which is an automated process, documented in the metadata for each shapefile, to generate catchments based on 1:24,000-scale NHD streams and “mgp” which is a manual, interactive process, documented in the metadata for each shapefile, to generate catchments to fill in the gaps (created by new processing) based on a flow raster from the PA StreamStats application. Not all directories have “new” and (or) “mgp” datasets. In 2012, automated processing for Strahler order 1 and 2 catchments was completed for 8-digit HUCs with Marcellus Shale (02040101 – 02040104, 02040106, headwaters of 02040203). Additional processing was completed between September 1, 2015 and September 30, 2016 for HUCs 02040101 through 02040104 and 02040106. As a result HUCS 02040101 through 02040104 and 02040106 have only mgp datasets for Strahler order 1 and 2. Due to the large tidal areas with low relief in HUCs 02040201, 02040202, and 02040205 through 02040207 only new processing was conducted. HUC 02040204 is the Delaware Bay water body. Non-tidal areas in HUCs 02040105, 02040201, 02040202, and 02040205 have both new and mgp datasets. HUC 02040105 had a very small tidal area with more measurable relief, therefore, new and mgp processing were completed. FGDC-compliant metadata specific to each shapefile can be found in files with the .xml extension.