Watershed Boundary Dataset (WBD) - USGS National Map Downloadable Data Collection

The Watershed Boundary Dataset (WBD) from The National Map (TNM) is a seamless, national hydrologic unit (HU) dataset. A HU defines the areal extent of surface water drainage to an outlet point on a dendritic stream network or to multiple outlet points where the stream network is not dendritic. A HU may represent all or only part of the total drainage area to an outlet point so that multiple HU may be required to define the entire drainage area at a given outlet. Hydrologic unit boundaries in the WBD are determined based on topographic, hydrologic, and other relevant landscape characteristics without regard for administrative, political, or jurisdictional boundaries. The WBD seamlessly represents hydrologic units at six required and two optional hierarchical levels. The HU in the WBD are arranged in a nested, hierarchical system with each HU in the system identified using a unique code. Hydrologic unit codes (HUC) are developed using a progressive two-digit system where each successively smaller areal unit is identified by adding two digits to the identifying code the smaller unit is nested within. WBD contains eight levels of progressive hydrologic units identified by unique 2- to 16-digit codes. The dataset is complete for the United States to the 12-digit hydrologic unit. The 14- and 16-digit hydrologic units are optional and are not complete for the nation. For additional information on NHD, go to https://www.usgs.gov/core-science-systems/ngp/national-hydrography.