Will the NHD replace the existing DLG-3 hydrography data?
The National Hydrography Dataset supersedes RF3 and DLG by incorporating them, not by replacing them. Users of RF3 or DLG will find the same data in a new, more flexible format. They will find the National Hydrography Dataset both familiar and greatly expanded and refined. What are ‘RF3’ and ‘DLG’? The U.S. Environmental Protection Agency’s (EPA) Reach Files are a series of national hydrologic databases that uniquely identify and interconnect the stream segments or “reaches” that comprise the country’s surface water drainage system. The three versions of the Reach File that currently exist, known as RF1, RF2, and RF3-Alpha respectively, were created from increasingly detailed sets of digital hydrography data produced by the U.S. Geological Survey. The EPA enhanced these hydrography datasets by assigning a unique reach code to each stream segment, determining the upstream/downstream relationships of each reach, and, when possible, identifying the stream name for each reach. DLG’s are ve
