A 14-digit hydrologic unit is a drainage sub-watershed that maintains a typical size of 10,000 to 40,000 acres, with minimum size of 3,000 acres. Each 14-digit HU is completely contained within one 11-digit HU. The 14-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.