Automated Geospatial Watershed Assessment

The Automated Geospatial Watershed Assessment (AGWA) tool is a Geographic Information Systems (GIS) interface jointly developed by the U.S. Environmental Protection Agency, the U.S. Department of Agriculture (USDA) Agricultural Research Service, and the University of Arizona to automate the parameterization and execution of the Soil Water Assessment Tool (SWAT) and KINematic Runoff and EROSion (KINEROS2) hydrologic models. The application of these two models allows AGWA to conduct hydrologic modeling and watershed assessments at multiple temporal and spatial scales. For large river basins, typically SWAT is employed. AGWA’s current outputs are runoff (volumes and peaks) and sediment yield, plus nitrogen and phosphorus with the SWAT model.

AGWA uses commonly available GIS data layers to fully parameterize, execute, and spatially visualize results from both SWAT and KINEROS2. Through an intuitive interface, users select an outlet from which AGWA delineates and discretizes the watershed using a Digital Elevation Model (DEM) based on the individual model requirements. The watershed model elements are then intersected with soils and land cover data layers to derive the requisite model input parameters. AGWA can currently use STATSGO, SSURGO and FAO soils and nationally available land-cover/use data such as the National Land Cover Data (NLCD) datasets. Users are also provided the functionality to easily customize AGWA for use with any classified land-cover/use data. The chosen hydrologic model is then executed, and the results are imported back into AGWA for visualization. This allows decision-makers to identify potential problem areas where additional monitoring can be undertaken or mitigation activities can be focused. AGWA can difference results from multiple simulations to examine and compare changes predicted for each alternative input scenario (e.g., climate/storm change, land-cover change, present conditions, and alternative futures). In addition, a variety of new capabilities have been incorporated into AGWA, including pre- and post-fire watershed assessment, watershed group simulations, implementation of stream buffer zones, and installation of retention and detention structures. A land-cover modification tool is provided for the development of prescribed land-cover change scenarios, with a number of options for uniform, spatially random, and patchy change to single or multiple land-cover classes. There are currently two versions of AGWA available: AGWA 1.5 for users with Environmental Systems Research Institute (ESRI) ArcView 3.x GIS software (ESRI, 2005), and AGWA 2.0 for users with ESRI ArcGIS 9.x (ESRI, 2006).