The National Hydrography Dataset (NHD) represents the water drainage network of the United States with features such as rivers, streams, canals, lakes, ponds, coastline, dams, and stream gages. Washington State uses this dataset as the standard for all of our water based GIS data. As the lead agency, Ecology is the steward of the Washington portion of the NHD and we work with our partners to produce high quality hydrography data.
For a more detailed review of NHD data in Washington State look at our StoryMap
Download NHD Data
NHD data is available in a couple different formats. For Washington, we publish the data a couple times a year and add “Stream Order” for a full state download. USGS provides continuous updates to the NHD but only at the HUC4 and HUC8 Watershed level.
Why Link Data to NHD?
While NHD is a great source for location of hydrography features, the real power is connecting collected attribute data to the NHD. The benefit of linking data to a single hydro dataset not only include sharing the efforts of mapping, but also the ability to cross compare different hydro data projects.
Rather than having the data recorded in the attribute table of the actual NHD feature, they are maintained in a separate file or dataset that can be linked back to the NHD using GIS. These data are linearly referenced to the NHD stream network using a system of routes (ReachCodes) and distances along the routes (Measures). Similar to a house number on a particular street, the ReachCode and Measure is a method of locating data on a particular reach of a stream.
Anyone can associate their data to NHD while maintaining full control of their data. Whenever an NHD reach is moved, the linked data can easily be reconnected to the new stream location using tools developed by USGS.