Introducing NHDPlus!

NHDPlus Version 1.0 is an integrated suite of application-ready geospatial data sets that incorporate many of the best features of the National Hydrography Dataset (NHD) and the National Elevation Dataset (NED). NHDPlus is the outcome of a multi-agency effort aimed at developing NHD flow volume and velocity estimates to support of pollution fate-and-transport models, such as the USGS SPARROW model. NHDPlus includes a stream network, based on the medium resolution NHD, improved networking, naming, and “value-added attributes” (VAAs). NHDPlus also includes elevation-derived catchments produced using a drainage enforcement technique first broadly applied in New England, and thus dubbed “The New-England Method”. This technique involves “burning-in” the 1:100,000-scale hydrography, and when available, building “walls” using the national Watershed Boundaries Dataset (WBD). The technique was enhanced to impose a “bathymetric gradient” in water bodies to ensure that catchments for centerline reaches passing through water bodies agree with the associated shorelines. The resulting modified digital elevation model (DEM) is used to produce hydrologic derivatives that closely agree with the NHD and WBD. An interdisciplinary team from the U. S. Geological Survey (USGS), U.S. Environmental Protection Agency (USEPA), and contractors, over the last two years has found this method to produce the best quality catchments feasible in a relatively short time frame.

 

The VAAs include greatly enhanced capabilities for upstream and downstream navigation, analysis and modeling. Examples include: stream order, retrieve all flowlines and catchments upstream of a given flowline using queries rather than by slower flowline-by-flowline navigation; subset a stream level path sorted in hydrologic order for stream profile mapping, analysis and plotting; and, calculate cumulative catchment attributes using streamlined VAA hydrologic sequencing routing attributes. The VAAs include results from the use of these cumulative routing techniques, such as cumulative drainage areas and land cover distributions. These cumulative attributes are used to estimate mean annual flow and velocity as part of the VAAs.

 

NHDPlus contains a snapshot of the 1:100,000 scale NHD that has been extensively improved.  While these updates will eventually make their way back to the central NHD repository at USGS, this cannot not happen prior to distribution of NHDPlus because the update process for the central NHD repository is still in development.  Consequently, the NHDPlus will contain some temporary database keys.  Therefore, NHDPlus users may not make additional updates to the NHD portions of NHDPlus with the intent of sending these additional updates back to the central NHD repository.  Once the NHDPlus updates have been posted to the central NHD respository, a fresh copy of the improved data can be pulled from the NHD web site and that copy will be usable for data maintenance.

 

As noted above, the geospatial data sets included in NHDPlus are used to develop estimates of mean annual streamflow and velocity for each NHD flowline in the conterminous United States. The results of these analyses are included with the NHDPlus data.

 

In addition, locations of approximately 22,000 USGS Stream Gages have been snapped to and checked against the NHD nationwide. The updated location data will be initially released in shapefile[1] form, but without reach indexing attributes (reach route, measure, etc.). This data set will be called “USGS Streamgage Network Locations for NHD Version June 2002 Medium Resolution”. Once the NHDPlus V1.0 data are ready for a hydrologic region, the gage locations will be snapped to this version of the NHD and will become known as “USGS Streamgage Network Locations for NHDPlus Version 1.0”. This will be distributed as a shapefile, but will include the reach address fields in the .dbf file, so it also can be used as an event table.

 

Other event tables for databases maintained by EPA, such as impaired waters, permitted dischargers, etc., will eventually become available, but may not be available immediately.

 

NHDPlus is currently under production and is planned to be completed by the end of 2005.  For additional information, please contact Tommy Dewald (dewald.tommy@epa.gov).

 

[1] Shapefile is a published, but proprietary, data format from the Environmental Systems Research Institute, Inc. (ESRI).  Use of trade names is for identification purposes only and does not constitute endorsement by the U.S. Geological Survey or the U.S. Environmental Protection Agency.