Federal standards and procedures for the National Watershed Boundary Dataset (WBD): Chapter 3 of Section A, Federal Standards, Book 11, Collection and Delineation of Spatial Data

The Watershed Boundary Dataset (WBD) is a seamless, national hydrologic unit dataset developed using the guidelines and specifications outlined in this document. A hydrologic unit defines the areal extent of surface-water drainage to an outlet point on a dendritic stream network or to outlet points where the stream network is not dendritic. A hydrologic unit may represent all or only part of the total drainage area to the outlet point so that multiple hydrologic units may be required to define the entire drainage area for a given outlet. Hydrologic unit boundaries in the WBD are determined on the basis of 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 mapped at a minimum of 1:24,000-scale in the United States, except for in Hawaii, the Caribbean, and the Pacific Islands, which are at 1:25,000-scale, and in Alaska, where the data range from the minimum required 1:24,000-scale to 1:63,360-scale. Hydrologic units in the WBD provide a standardized base for water-resources organizations to locate, store, retrieve, and exchange hydrologic data; to index and inventory hydrologic data and information; to catalog water-data acquisition activities; and to use in a variety of other applications.

The specifications and procedures established in this document are intended to provide guidelines and best practices to local, regional, and national partners for delineating and updating the hydrologic units of the WBD. Maintaining the WBD using consistent practices improves watershed management through efficient sharing of information and resources and by ensuring that digital geographic data can be used with other related geographic information system data. Edits and additions to the hydrologic units are reviewed against this specification prior to inclusion to the national WBD.