A watershed is a geographic area into which the surrounding waters, sediments, and dissolved materials drain, and whose boundaries extend along surrounding topographic ridges. Each watershed or unit has a unique hydrologic unit code (HUC). Hydrologic unit codes are a USGS cataloging system that arranges watersheds from the largest area or region (2 digits - 03) to the smallest (12 digits - 030502020101).
Watershed-based water quality management recognizes the interdependence of water quality related activities associated with a drainage basin including: monitoring, problem identification and prioritization, water quality modeling, planning, permitting, and other activities. Watershed-based management allows the Agency to address Congressional and Legislative mandates and fulfill EPA reporting requirements including activities under Sections 303(d), 305(b), 314, and 319 of the Clean Water Act. The watershed approach also improves communication between SCDHEC, the regulated community, and the public on existing and future water quality issues.