What is a hydrologic unit code (HUC)?
Hydrologic Unit Codes (HUCs) are part of a U.S. Geologic Survey (USGS) watershed classification system based on size. For management and analysis purposes, hydrologic units are defined as the area that drains to a stream segment between an upstream-downstream pair of points. Under this system, the United States is divided into major watersheds such as the Mississippi River, and then further divided into subwatersheds. Each watershed is represented by a unique 8, 10 or 12-digit code commonly known as a HUC. 8-digit HUC’s are the largest and include major South Carolina rivers like the Catawba or Savannah while 12-digit HUC’s are the smallest. In 2008, USGS released a nationwide GIS data set for watershed boundaries to provide consistency across all fifty states. While South Carolina used a 11- and 14-digit HUC system for some years, the State has now adopted a 10- and 12-digit HUC system. As a result of the adoption of the national layer, few watershed boundaries were changed when they
