NHD Data Availability

The National Hydrography Dataset (NHD) is stored in a geodatabase implementation of the NHD model. This provides great flexibility and efficiency to allow the data to work well in analysis using a geographic information system (GIS). To maximize the capability of the NHD, users should download the data in a file-based or personal geodatabase known as NHDinGEO. For those using the NHD to create simple maps, a shapefile version known as NHDinSHAPE also is available.

The NHD data are easily accessible through this website. There are two ways to access the data. Both methods are based on the organization of hydrographic data into hydrologic units. These are drainage areas nested in a four-level hierarchy with a 2-digit identifier for each level.

• The first method allows the use of an interactive viewer to select subbasin units at the fourth level of the hierarchy. Zoom into to an area of interest until the 8-digit subbasin units appear and select the appropriate subbasins. Follow the instructions provided in the “How to Extract” icon. The data will be packaged and made available via email notification, which usually takes 1 to 2 hours.
  Go to NHD Viewer NHD Geodatabase
• The second method is based on pre-staging the NHD into second-level 4-digit subregion units. Go the appropriate high, medium, or local resolution folder and select the desired files for instant download. The NHD Viewer can be used to help find the desired 4-digit file.
  Go to Pre-staged Subregions

Using the NHD Viewer, additional data themes can be overlaid to help identify the area of interest. These themes include shaded terrain, boundaries, transportation, cities, map graphics, aerial imagery, and others. You can also visit EPA's Surf Your Watershed Web site if you need to locate the subbasin of interest to you, or don't know the subbasin number.

The NHD data are stored and made available at two levels of resolution: one is nominally at 1:24,000-scale known as high resolution, and the other is at 1:100,000-scale known as medium resolution. A limited amount of data are available at nominally 1:5,000-scale known as local resolution. The high resolution level may contain a mixture of scales at 1:24,000-scale or higher.

Click here to go the NHD Quickstart User Guide

Click here for information about the NHD data structure

The NHD data are organized into several forms of geometry and into several supporting tables:

Geometry: The geodatabase contains two Feature Datasets of geometry. The Hydrography feature dataset contains the NHD whereas the Hydrographic Units feature dataset contains the Watershed Boundary Dataset (WBD).

Hydrography: This feature dataset contains nine forms of geometry known as Feature Classes. The most critical is NHDFlowline.

NHDFlowline: This is the fundamental flow network consisting predominantly of stream/river and artificial path vector features. It represents the spatial geometry, carries the attributes, models the water flow, and contains linear referencing measures for locating events on the network. Additional NHDFlowline features are canal/ditch, pipeline, connector, underground conduit, and coastline.

Two types of polygons represent area features.

NHDWaterbody: Basic waterbodies such as lake/pond features are represented here. They portray the spatial geometry and the attributes of the feature. These water polygons may contain NHDFlowline artificial paths to allow the representation of water flow. Other NHDWaterbody features are swamp/marsh, reservoir, playa, estuary, and ice mass.

NHDArea: This feature class contains many additional features of water polygons. One of the more important is the stream/river feature. It represents the aerial extent of the water in a wide stream/river with a basic set of attributes. They typically contain NHDFlowline artificial paths that are used to model the stream/river. Artificial path carries the critical attributes of the stream/river, whereas NHDArea represents the geometric extent.

Two other feature classes are used to represent features. NHDLine contains linear features not core to the network, and NHDPoint contains hydrography related point features.

Finally, an additional three feature classes represent point, line, and area data events that behave as map features and linearly referenced events. Streamgages, which are point features, can be displayed and identified in the network through linear referencing with a network address. These feature classes are NHDPointEventFC, NHDLineEventFC, and NHDAreaEventFC.

Tables: Information about the NHD also can be obtained in a series of associated tables. This includes metadata stored in NHDFeaturetoMetadata and NHDMetadata, sources given in NHDSourceCitation, identification of model and data version given in NHDProcessingParameters, flow relations given in NHDFlow, reach code histories given in NHDReachCrossReference, the domain of feature codes given in NHDFCode, and others.