Hydrological Unit MapsAuthor: Federal
Media Type: Website
Water Monitoring Keywords: Mapping Tools
Watershed 101 Keywords: Watershed Geography
Water Resource Type: Broadly Applicable
Resource Link: Click Here
Specific Agency Author: United States Geological Survey (USGS)
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 or nested within each other, from the largest geographic area (regions) to the smallest geographic area (cataloging units). 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.