HMS Prepro, an ArcView GIS application, was used to develop a hydrologic model for the Buffalo Bayou watershed, which covers most of the Houston metropolitan area. The study area includes the Addicks and Barker Dam and Reservoir, which primarily serve as flood control. The watershed was delineated from USGS digital elevation models (DEMs) at 30-meter cell resolution and stream data from USGS digital line graph (DLG) and EPA river reach file (RF1). Physical watershed parameters were extracted from the HMS Prepro program to support hydrologic parameters computation. The model uses grid-based radar (NEXRAD) rainfall in Standard Hydrologic Grid.