Integration of watershed tools and SWAT model into BASINS

BASINS (Better Assessment Science Integrating Point and Nonpoint Sources) version 3.0, is the updated software system developed by the U.S. Environmental Protection Agency Office of Water in order to meet the requirements of developing Total Maximum Daily Load (TMDL) programs. BASINS provides an enhanced set of nation-wide databases, several new and interchangeable tools and models integrated in a new modular architecture, operating within ArcView Geographical Information System (GIS) for desktop PCs. This paper describes the integration of three new key components: (1) a tool that optimizes the automatic definition and segmentation of the watershed and stream network based on topography (Digital Elevation Models), NHD (National Hydrography Dataset) or other ancillary stream data; (2) a tool to define the Hydrologic Response Units (HRUs) over the watershed and subwatersheds; and (3) SWAT (Soil and Water Assessment Tool) model and a respective integrated user-friendly interface. The first two components, based on raster functionality, improve the previously adopted simplistic methods for the hydrologic definition, segmentation and basic geomorphic assessment of the watershed and open to the usage of external datasets besides those distributed with the whole BASINS package. In addition, these components share generating datasets, hereby promoting the usage by other tools and models as well as other models that in the future could be introduced in BASINS. The third component introduces the SWAT model into BASINS. SWAT is a hydrologic distributed model with proven success in watershed assessment of both agricultural and urban scenario management effects on water quality and is based on over 30 years of USDA modeling experience. The description of these integrated components is followed by a simple, yet promising, application to the Upper North Bosque River watershed in Texas, using the default data distributed with BASINS.