NHD/WBD Update

The Arkansas GIS Office is pleased to announce an update to the  National Hydrography Dataset and Watershed Boundary Dataset.  Also an additional housekeeping item is the renaming the Watershed Boundary products from Basins HUC # to WBD HU # which will hopefully make finding them a little easier. Please note that for the time being we have retained the 2006 Watershed Boundary products and map/feature services to provide a transition period to the 2017 data. They are distinguishable by date at which they were last sourced.   The 2006 data was originally sourced from NRCS and  whereas the 2017 data was sourced from USGS.  The update to the NHD is only to High Resolution at this time as the Medium resolution has transitioned back to the EPA as the primary custodian.   We’d like to thank all agencies involved in the maintenance of this critical dataset.

Both data sets can be viewed and downloaded by searching for NHD or WBD respectively or can be accessed via feature services at http://gis.arkansas.gov/arcgis/rest/services/FEATURESERVICES/Water/FeatureServer

The National Hydrography Dataset (NHD) is a feature-based database that interconnects and uniquely identifies the stream segments or reaches that make up the nation’s surface water drainage system. NHD data was originally developed at 1:100,000-scale and exists at that scale for the whole country. This high-resolution NHD, generally developed at 1:24,000/1:12,000 scale, adds detail to the original 1:100,000-scale NHD. (Data for Alaska, Puerto Rico and the Virgin Islands was developed at high-resolution, not 1:100,000 scale.) Local resolution NHD is being developed where partners and data exist. The NHD contains reach codes for networked features, flow direction, names, and centerline representations for areal water bodies. Reaches are also defined on waterbodies and the approximate shorelines of the Great Lakes, the Atlantic and Pacific Oceans and the Gulf of Mexico. The NHD also incorporates the National Spatial Data Infrastructure framework criteria established by the Federal Geographic Data Committee.

The Watershed Boundary Dataset (WBD) is a comprehensive aggregated collection of hydrologic unit data consistent with the national criteria for delineation and resolution. It defines the areal extent of surface water drainage to a point except in coastal or lake front areas where there could be multiple outlets as stated by the “Federal Standards and Procedures for the National Watershed Boundary Dataset (WBD)” “Standard” (http://pubs.usgs.gov/tm/11/a3/). Watershed boundaries are determined solely upon science-based hydrologic principles, not favoring any administrative boundaries or special projects, nor particular program or agency. This dataset represents the hydrologic unit boundaries to the 12-digit (6th level) for the entire United States. Some areas may also include additional subdivisions representing the 14- and 16-digit hydrologic unit (HU). At a minimum, the HUs are delineated at 1:24,000-scale in the conterminous United States, 1:25,000-scale in Hawaii, Pacific basin and the Caribbean, and 1:63,360-scale in Alaska, meeting the National Map Accuracy Standards (NMAS). Higher resolution boundaries are being developed where partners and data exist and will be incorporated back into the WBD. WBD data are delivered as a dataset of polygons and corresponding lines that define the boundary of the polygon. WBD polygon attributes include hydrologic unit codes (HUC), size (in the form of acres and square kilometers), name, downstream hydrologic unit code, type of watershed, non-contributing areas, and flow modifications. The HUC describes where the unit is in the country and the level of the unit. WBD line attributes contain the highest level of hydrologic unit for each boundary, line source information and flow modifications