Federal Standards for Delineation of Hydrologic Unit Boundaries

Document number

not applicable

Maintenance authority

not applicable


Provide guidelines for the development of a nationally consistant set of watersheds and subwatersheds (hydrologic units) using an extension of existing standard codes for identification of hydrologic units in the United States, the U.S. Caribbean and Pacific island territories.

To create watershed (level 5, 10-digit) and subwatershed (level 6, 12-digit) hydrologic units as defined by an interagency standard.  The new watershed and subwatershed hydrologic units developed using scientific hydrologic and mapping principles through one standard will be the foundation for creating a national Watershed Boundary Dataset (WBD).  


The interagency standard will set forth terminology, definitions, and guidelines to ensure the uniform development of hydrologic unit boundaries by the agencies, tribes and organizations that develop, manage, archive, exchange, and analyze data by hydrologic features.  The standard will enable a variety of users from different agencies and programs to contribute to an overall coordinated watershed management approach, efficiently share information and resources, and assure the geospatial database is usable with other related Geographic Information System (GIS) databases.

The criteria and methods for hydrologic unit selection and boundary delineation will permit standardized hydrologic units to be used by a diverse group of users serving multi-agency programs.  Some examples of these programs include watershed management, water quality initiatives, watershed modeling, resource inventory and assessment, and establishing total maximum daily loads.  The utility of hydrologic units of various size and complexity based primarily on natural surface water flow and topographic landforms cannot be underestimated for the potential valuable analytical and statistical purposes and applications at hydrological and ecosystem scales.

Sponsored by

Subcommittee on Spatial Water Data

Project history

Proposal  2001-07-31  FGDC Standards Working Group
Working draft 1.1
2003-12-23  Spatial Water Data Subcommittee