This document provides an overview of watershed delineation using digital elevation models (DEMs) with ArcGIS. It discusses key steps in the hydrological modeling process including downloading and preprocessing DEMs, generating flow directions and accumulating flows, delineating sub-basins, and computing watershed parameters. The document also mentions data needs for hydrological modeling, including geographic data like lengths, areas, slopes and hydrological data like runoff coefficients, infiltration, and rainfall statistics.