An 11-digit hydrologic unit is a drainage watershed that maintains a typical size of 40,000 to 250,000 acres. Each 11-digit HU is completely contained within one 8-digit HU. The 11-digit HU boundaries are delineated by NRCS based on 1:24000 scale USGS topographic maps. NRCS is updating hydrologic unit boundaries. Click here for more information.