AGRICULTURAL AND WATERSHED MODELING WITH EPIC, APEX, AND SWAT: COMPUTATIONAL TOOLS FOR INVESTIGATING, PLANNING, AND UNDERSTANDING THE FUTURE

Abstract

   Scientists from Texas A&M AgriLife Research and the United States Department of Agriculture – Agricultural Research Service have worked together at the Blackland Research Center (BRC) in Temple, Texas for more than 80 years. Since the mid-1960's, computer models describing agricultural, environmental, and hydrological processes have been developed by scientists at BRC. Today BRC scientists continue to refine and support numerous modeling products that are used world-wide by researchers, environmental managers, and government policy makers. The Environmental Policy and Integrated Climate (EPIC) model, the Agricultural Policy and Environmental eXtender (APEX) model, and the Soil and Water Assessment Tool (SWAT) are the most prominent and heavily used. This paper briefly describes their history, general organization, usage tools, support and availability, and three example uses. In the first example, the EPIC model was used to evaluate irrigation control methods on an urban landscape. The uncalibrated results suggested that scheduled irrigation was more efficient than sensor-based. This was unexpected but explained by poor plant growth under water-saturated soil conditions. In another example, a calibrated SWAT model was used to determine sediment sources and evaluate a detention pond management strategy in a heavily developed urban watershed. Stream channel erosion was found to be higher than upland erosion and the implementation of a sediment detention pond showed that sediment exports could be reduced by up to 14%. Finally, the APEX model was used to examine two irrigation strategies in cascading rice paddy fields. Data from Okayama, Japan was used to develop a terraced hydrology model and predict irrigation management practice effects on water useage and soil and nitrogen exports to downstream waterbodies. The uncalibrated model showed that constant flooding irrigation produced higher crop yields but also increased sediment exports. Cycled flooding however showed reduced nitrogen exports. Determining the optimial management strategy depends upon user goals.