A U.S. GEOLOGICAL SURVEY DATA STANDARD Codes for the Identification of Hydrologic Units in the United States and the Caribbean Outlying Areas GEOLOGICAL SURVEY CIRCULAR 878-A This report describes one of a series of data standards adopted and im- plemented by the U.S . Geological Survey for the standardization of data elements and representation:; used in automated Earth-science systems. Earth sciences are those scientific disciplines especially required to carry out the mission of the Geological Survey and are concerned with the material and morphology of the Earth and physical forces relating to the Earth. These disciplines include geology, topography, geography, and hydrology. The Geological Survey has assumed the leadership in developing arid main- taining Earth-science data element and representation standards for use in the Federal establishment under the terms of a Memorandum of Understand- ing signed in February 1980 by the National Bureau of Standards of the Department of Commerce and the Geological Survey, a Bureau of the Depart- ment of the Interior. As such., in addition to developing and maintaining standards, the Geological Survey reviews and processes all requests referred by the National Bureau of Standards for exceptions, deferments, and revi- sion of standards applicable to Federal Earth-science information systems; assists the National Bureau of Standards in assessing the need, impact, benefits, and problems related to the implementation of standards being con- sidered for development, or developed, for use in the Earth sciences ; and works with other agencies in developing new data standards in the Earth sciences. The standard described in this report has been specifically approved for use within the U.S . Geological Survey. If the standard has been approved for use throughout the Federal establishment, it is also published by the National Bureau of Standards as a Federal Information Processing Standard. Name of Standard: Codes for the Identification of Hydrologic Units in the United States and the Caribbean Outlying Areas Date of Approval: July 1981 Maintenance Organization: U.S . Geological Survey Water Resources Division Office of Water Data Coordination 41.7 National Center Reston, VA 22092 Questions concerning the list of entities and codes should be addressed to the Office of Water Data Coordination, which will make all necessary amendments to the standard. Implementation: All Geological Survey data standards are effective iin- mediateiy upon the date of approval. Their use is mandatory for all new and developing systems within the Geological Survey that utilize data elements and representations described by the standards. All existing data systems will be modified in accordance with the standards at such time that future redesign and modifications to the systems take place. Additional information about Geological Survey data standards and copies of published standards may be obtained from : Data Administrator U.S. Geological Survey 115 National. Center Reston, VA 22092 Telephone: ('703) 850-6080 FTS 928-6086 A U .S . GEOLOGICAL SURVEY DATA STANDARD Codes for the Identification of Hydrologic Units in the United States and the Caribbean Outlying Areas GEOLOGICAL SURVEY CIRCULAR 878-A United States Department of the Interior JAMES G. WATT, Secretary Geological Survey Dallas L. Peck, Director Free on application to Distribution Branch, Text Products Section, U. S. Geological Survey, 604 South Pickett Street, Alexandria, VA 22304 CONTENTS Page Introduction ________-__________._______________-_-_____________________-__________ At Development of the codes -------------------------------------------------------------- At Description of the codes --------------------------------------------------------------- AI Hydrologic unit names _______ .____.________________-___________-___________-________. A3 Hydrologic unit codes-Boundary descriptions and names of regions, subregions, accounting; units, and cataloging units ------------------------------------------------------------- A4 ILLUSTRATION Page FIGURE 1 . Map of water-resources regions snowing accounting units of the National Water Data Network A2 Codes four the Identification of Hydrologic Units in the, United States and the Caribbean Outlying Areas INTRODUCTION Resources Division, in conjunction with their prin- cipal regional, State, and local cooperators, fol- This report presents and describes codes used for lowed by review and approval[ by the National the identification of hydrologic units in the United Planning and Assessment Committee (NPAC) of States and the Caribbean outlying areas. The codes the WRC. NPAC consisted of members from all identify a hydrologic system that; divides the principal Federal agencies involved with water- United[ States and the Caribbean into 21 major resources planning. Approval. by the NPAC con- regions . These :regions are further subdivided into stituted approval by the Council of Represent- approximately 2,150 units that delineate river atives of the WRC, which had delegated this basins having drainage areas usually greater than authority to the NPAC . 700 square miles. The codes provide a standardized base for use by water-resources organizations in the storage, retrieval., and exchange of hydrologic DESCRIPTION OF THIE CODES data; the indexing and inventorying of hydrologic data and information ; the cataloging of water-data All hydrologic limits have been identified by a acquisition activities;; and a variety of other ap- unique hydrologic unit code consisting of from two plications. to eight digits based on the four levels of classifica- tion in the hydrologic unit system. DEVELOPMENT OF THE: CODES The first level of classification divides the Nation In 1974, a new set of maps (State Hydrologic into 21 major geographic areas or regions-18 in Unit T)/Iaps) depicting approved boundaries and the conterminous United States and. one each in codes of river basins of the United States was pro- Alaska, Hawaii, and the Caribbean (fig. 1) . These duced by the U .S. Geological Survey (USGS) in geographic areas (hydrologic areas based on sur- cooperation with the U.S. Water Resources Coun- face topography) contain either the drainage area cil (WRC) . These maps present information on of a major river, such as the Missouri Region, or drainage, culture, hydrography, and hydrologic the combined drainage areas of a series of rivers, boundaries of (1) WRC regions, (2) WRC planning such as the Texas-Gulf Region, which includes a subregions, (3) National Water, .D~ata. Network ac- number of rivers draining into the Gulf of Mexico. counting units, and (4) cataloging units of the The second level. of classification divides the 21 USGS "Catalog of Information on 'Water Data." regions into 222 planning subregions . A planning These :four levels of subdivisions, used for the col- subregion includes the area drained by a river lection and organization of hydrologic data, are system, a reach of :a river and its tributarie=s in that "hydrologic units ." The codes associated with these reach, a closed basin or basins, or a group of units are "hydrologic unit codes." streams forming a coastal drainage area. The hydrologic unit boundaries, codes, and The third level of classification subdivides many names were reviewed extensively by all principal of the planning subregions into accounting; units. Federal, regional, and State water-resources agen- These 352 hydrologic accounting; units nest, within cies during a formal review process established for or are equivalent to the planning subregions. The the State Hydrologic Unit Maps. The forinal accounting units are used by the USGS for design- review process consisted of a field review by the 4 ing and managing the National Water Data Net- regional and 46 district offices of the USGS Water work. A1 'v FIGURE 1.-Map of water-resources regions showing accounting units of the National Water Data Network. The fourth level of classification is the catalog- are one and the same. Likewise, if the cataloging ing unit, the smallest element in the hierarchy of unit code is 00, it is the same as the accounting hydrologic units . A cataloging unit is a geo- unit. graphic area representing part or all of a surface drainage basin, a combination of drainage basins, HYDROLOGIC UNIT NAMES or a distinct hydrologic feature. These units sub- divide the planning subregions and. accounting In addition to hydrologic unit units into smaller areas (approximately 2,150 in codes, all the Nation) that are used for cataloging and index- hydrologic units have been assigned names cor- ing water-data acquisition activities. responding to the principal hydrologic feature(s) An eight-digit code is used to allow each of the within the unit or, in the absence of such, to a prin- four levels of classification to be uniquely identified cipal geographic or physical feature within the within four two-digit fields . The first two digits unit. In the absence of such features, the assigned identify the water-resources region; the planning name may reflect a cultural or political feature subregion is identified by the first four digits; the within the unit. A.11 regions and subregions are accounting unit is identified by the first six digits; uniquely named; however, the accounting units are and the addition of the cataloging unit number uniquely named only within each region, and the completes the eight-digit code . An example is cataloging units are uniquely named only within given below using hydrologic unit code 010802(14: each