Water Resources of the United States


WATER DATA FOR THE NATION

National Water Information System (NWIS)

View current and historical streamflow, groundwater level, and water-quality data

Data Discovery

For more data options, explore our data discovery tools.

Today's Water Conditions

View maps of current and historical conditions

Click map to go to current water resources conditions in the U.S.

Subscribe to hydrologic alerts:

WATER SCIENCE SPECIALTIES

WATER SCIENCE BY STATE

USGS Water Science Centers are located in each state

Hydrologic Unit Maps


What are Hydrologic Units?

Adapted from Seaber, P.R., Kapinos, F.P., and Knapp, G.L., 1987, Hydrologic Unit Maps: U.S. Geological Survey Water-Supply Paper 2294, 63 p. Updated information not from this source is enclosed in square brackets below. A copy of USGS Water-Supply Paper 2294 may be ordered from USGS Information Services

The United States is divided and sub-divided into successively smaller hydrologic units which are classified into four levels: regions, sub-regions, accounting units, and cataloging units. The hydrologic units are arranged within each other, from the smallest (cataloging units) to the largest (regions). Each hydrologic unit is identified by a unique hydrologic unit code (HUC) consisting of two to eight digits based on the four levels of classification in the hydrologic unit system.

Map of Water Resources Regions
[Figure 1. Map of Water Resources Regions] Click for a larger (13K) image.

The first level of classification divides the Nation into 21 major geographic areas, or regions. These geographic areas contain either the drainage area of a major river, such as the Missouri region, or the combined drainage areas of a series of rivers, such as the Texas-Gulf region, which includes a number of rivers draining into the Gulf of Mexico. Eighteen of the regions occupy the land areaof the conterminous United States. Alaska is region 19, the Hawaii Islands constitute region 20, and Puerto Rico and other outlying Caribbean areas are region 21. [The regions are shown in figure 1.]

The second level of classification divides the 21 regions into 221 subregions. A subregion includes the area drained by a river system, a reach of a river and its tributaries in that reach, a closed basin(s), or a group of streams forming a coastal drainage area.

The third level of classification subdivides many of the subregions into accounting units. These 378 hydrologic accounting units are nested within, or can be equivalent to the subregions.

The fourth level of classification is the cataloging unit, the smallest element in the hierarchy of hydrologic units. [Efforts are underway to add further levels (5th and 6th levels) of subdivisions,.see the Watershed Boundary Dataset WBD] A cataloging unit is a geographic area representing part of all of a surface drainage basin, a combination of drainage basins, or a distinct hydrologic feature. These units subdivide the subregions and accounting units into smaller areas. There are 2264 Cataloging Units in the Nation. [Cataloging Units sometimes are called "watersheds." See, for example, the USGS Science in Your Watershed or the EPA Surf Your Watershed site.]

List of Hydrologic Units

Download the text-formatted list of hydrologic units names and numbers from USGS Water-Supply Paper 2294. in either the original format or in tab-delimited format. Please note: Alaskan HUC numbers have changed since publication of WSP 2294. The list is not current for Alaska.

Paper Maps

A single-sheet hydrologic unit map of the U.S. is available published at a scale of 1:3,500,000 and the map measures 41- by 58-inches. This map is part of The National Atlas of the United States of America series. "Hydrologic Units" is available from USGS at a cost of $7.00 per sheet. Its stock number is TUS5681. The "Hydrologic Units" atlas map supersedes both the "Hydrologic Unit Map of the United States, East" (GHU0057-1T) and the "Hydrologic Unit Map of the United States, West" (GHU0057-2T). Additional information regarding this map is available at:

http://www.nationalatlas.gov/wallmaps.html#hydro.

Paper maps may be ordered from USGS Information Services

Digital Spatial Data Sets

Digital Map Example

View of huc2m coverage.

 

 

The Most Proper List of the HUC 8-digit, 10-digit, and the 12-digit Codes, Values and Names are in the Watershed Boundary Dataset.

 

1:2,000,000-scale Hydrologic Units (huc2m)
The coverage is available on line, at no charge, via links from the metadata file.

1:250,000-scale Hydrologic Units (huc250k)
The data for this large coverage was originally collected for the Geographic Information Retrieval and Analysis System (GIRAS) at a scale of 1:250K. Some areas, notably major cities in the west, were recompiled at a scale of 1:100K. The coverage was compiled to provide the National Water Quality Assessment (NAWQA) study units with an intermediate- scale river basin boundary for extracting other GIS data layers.

The coverage is available on line, at no charge, via links from the file. It may be retrieved as a single file for the lower 48 States.

The following is the link to the official Alaska 1:250k HUC coverage: http://agdc.usgs.gov/data/projects/anwr/metadata/akhuc.html

Hawaii and Puerto Rico will be updated when available.

The Watershed Boundary Dataset (WBD) - is a nationally consistent watershed dataset that is subdivided into 6 levels (12-digit hucs) and is available from the USGS and USDA-NRCS-National Cartographic and Geospatial Center's (NCGC). The new 8-digit WBD (125 megabytes) and the new 12-digit WBD (933 megabytes) are available as geodatabases for download, along with the metadata. The directory all the files reside are located here .

USGS Home Water Climate Change Science Systems Ecosystems Energy, Minerals, & Env. Health Hazards USGS Intranet

Accessibility FOIA Privacy Policies and Notices

Take Pride in America logo USA.gov logo U.S. Department of the Interior | U.S. Geological Survey
URL: http://water.usgs.gov/GIS/huc.html
Page Contact Information: Water Webserver Team
Page Last Modified: Tuesday, 03-Jan-2012 11:04:13 EST