USGS Hydrologic Units
Authored By: P. A. Flebbe
During the 1970s the U.S. Geological Survey (USGS) developed a hierarchical hydrologic unit code (HUC) system that divides the United States into 21 regions, 222 subregions, 352 accounting units, and 2,149 cataloging units based on surface hydrologic features, or drainages. The smallest USGS unit, the 8-digit HUC (or 4th level HUC), averages about 448,000 acres, and is usually the level referred to as a "HUC".
Seventy-two HUCs are wholly or partly in the southern Appalachians.
Encyclopedia ID: p1516
