USGS National Hydrography Dataset (NHD)
The National Hydrography Dataset (NHD) is the U.S. Geological Survey's authoritative geospatial representation of the surface water features of the United States, including rivers, streams, canals, lakes, ponds, and other waterbodies. The associated NHDPlus products add value with flow direction, network connectivity (NHDFlowline), waterbody features (NHDWaterbody), and catchment attributes. SAWGraph uses NHD and NHDPlus data as a geospatial reference source for modeling surface water features and the flowlines that connect them, supporting spatial context for PFAS observations.
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