Watershed Boundary Dataset, 12-Digit Hydrologic Units

The 12-Digit Hydrologic Units, a component of the Watershed Boundary Dataset (WBD), depict the sixth level hydrologic subdivision of the United States. A hydrologic unit can accept surface water from upstream drainage areas and may define a drainage area with single or multiple outlet points. A 12-digit hydrologic unit, or subwatershed, supports water resource management and planning activities at a localized and site-specific level. There are 101,779 12-digit hydrololgic units with an average size of 41 square miles (107 sq. km.).

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