Raster-based elevation data (DEMs) is very suitable for hydrologic modeling using efficient and useful algorithms for terrain analysis to delineate watershed boundaries and stream networks. Although DEMs are available from the USGS at different space resolutions, the discrete elevation resolution still remains a major drawback. The U.S. Environmental Protection Agency (EPA) Reach Files are a series of hydrographic databases of the surface waters of the continental United States, created expressly to provide hydrologic ordering as well as network navigation. ArcView GIS software was used to develop a set of tools to improve the watershed and stream network definitions matching USGS and USEPA databases.