NHD Descriptions

NHDArea

Description: NHDArea is a subset of the National Hydrography Dataset (NHD). The NHDArea feature class is used to delineate polygonal water features, such as rivers.


Title: Rivers and Other Polygonal features as defined by the National Hydrography Dataset.


NHDFlowline

Description: NHDFlowline is a subset of the National Hydrography Dataset (NHD). The NHDFlowline is used to delineate linear water features, such as streams and canals.


Title: Streams, Canals and other linear features as defined by the National Hydrography Dataset.


NHDLine

Description: NHDLine is a subset of the National Hydrography Dataset (NHD). The NHDLine feature class is used to delineate features using lines, such as sewer lagoons and dams.


Title: Dams and Lagoons as defined by the National Hydrography Dataset.


NHDPoint

Description: NHDPoint is a subset of the National Hydrography Dataset (NHD). The NHDpoint feature class is used to delineate point features, such as springs, wells and gaging stations.


Title: Wells, springs and other point features as defined by the National Hydrography Dataset.


NHDWaterbody

Description: NHDWaterbody is a subset of the National Hydrography Dataset (NHD). The NHDWaterbody feature class is used to delineate polygonal water features, such as lakes and marshes.


Title: Lakes, marshes and other polygonal features as defined by the National Hydrography Dataset.


HYDRO_NET_Junctions

Description: HYDRO_NET_Junctions is a subset of the National Hydrography Dataset (NHD). HYDRO_NET_Junctions displays the connection points for the NHDFlowline feature class. So it allows the user to see locations where flow splits or comes together.


Title: Connection point features as defined by the National Hydrography Dataset.


HYDRO_NET

Description: HYDRO_NET is an ArcGIS topology of the National Hydrography Dataset (NHD). The topology is composed of NHDFlowline and HYDRO_NET_Junctions. HYDRO_NET can be used for modeling water movement through the network.


Title: Topology for the National Hydrography Dataset.


Hydrologic Units

The six different levels of hydrologic units are shown below.


Hydrologic Unit Level Name Digits Size Units
1 Region 2 Average:177,560 square miles 21
2 Sub-region 4 Average: 16,800 square miles 222
3 Basin 6 Average: 10,596 square miles 352
4 Sub-basin 8 Average: 703 square miles 2,149
5 Watershed 10 63-391 square miles (40,000-250,000 acres) 22,000 (estimate)
6 Subwatershed 12 16-63 square miles (10,000-40,000 acres) 160,000 (estimate)

Region

Description: The Region feature class is a subset of the National Hydrography Dataset (NHD). Polygons portrayed in this feature class have an average size of 177,560 square miles. Regions are classified as a first level - two digit hydrologic unit code (HUC) by the United States Geological Survey (USGS) and Natural Resource Conservation Service (NRCS).


Title: Region - National Hydrography Dataset – Empty Dataset.


Sub-region

Description: The Subregion feature class is a subset of the National Hydrography Dataset (NHD). Polygons portrayed in this feature class have an average size of 16,800 square miles Subregions are classified as a second level - four digit hydrologic unit code (HUC) by the United States Geological Survey (USGS) and Natural Resource Conservation Service (NRCS).


Title:Subregions - National Hydrography Dataset.


Basin

Description: The Basin feature class is a subset of the National Hydrography Dataset (NHD). Polygons portrayed in this feature class have an average size of 10,596 square miles. Basins are classified as a third level - six digit hydrologic unit code (HUC) by the United States Geological Survey (USGS) and Natural Resource Conservation Service (NRCS).


Title: Basins - National Hydrography Dataset.


Sub-basin

Description: The Subbasin feature class is a subset of the National Hydrography Dataset (NHD). Polygons portrayed in this feature class have an average size of 703 square miles. Subbasins are classified as a fourth level - eight digit hydrologic unit code (HUC) by the United States Geological Survey (USGS) and Natural Resource Conservation Service (NRCS).


Title: Subbasin - National Hydrography Dataset.


Watershed

Description: The Watershed feature class is a subset of the National Hydrography Dataset (NHD). Polygons portrayed in this feature class have an average size of 63-391 square miles (40,000-250,000 acres). Watersheds are classified as an fifth level - eleven digit hydrologic unit code (HUC) by the United States Geological Survey (USGS) and Natural Resource Conservation Service (NRCS).


Title: Watersheds - National Hydrography Dataset – Empty Dataset.


Subwatershed

Description: The Subwatershed feature class is a subset of the National Hydrography Dataset (NHD). Polygons portrayed in this feature class have an average size of 16-63 square miles (10,000-40,000 acres). Subwatersheds are classified as a sixth level - fourteen digit hydrologic unit code (HUC) by the United States Geological Survey (USGS) and Natural Resource Conservation Service (NRCS).


Title: Subwatersheds - National Hydrography Dataset – Empty Dataset.