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Application of SWAT and APEX Models Using SWAPP (SWAT/APEX Program) for Upper North Bosque River Watershed in Texas

Published by the American Society of Agricultural and Biological Engineers, St. Joseph, Michigan

Citation:  Watershed Management to Meet Water Quality Standards and Emerging TMDL (Total Maximum Daily Load) Proceedings of the Third Conference 5-9 March 2005 (Atlanta, Georgia USA) Publication Date 5 March 2005  701P0105.(doi:10.13031/2013.18119)
Authors:   Ali Saleh
Keywords:   Water quality, GIS, SWAT, APEX, modeling, nutrient, sediment

In response to the Clean Water Act in early 1970s, the Agricultural Research Service (ARS) branch of United States Department of Agriculture (USDA) initiated the development of several processed-based nonpoint source models. These models are used to assess and evaluate various BMPs (best management practices) at field (using Agricultural Policy/Environmental eXtender, APEX) and watershed (using Soil Water Assessment Tool, SWAT) levels. However, these models are capable of simulating a limited number of scenarios individually. For example, APEX is capable of simulating scenarios such as multi-cropping, filter strips, and farm-level animal production systems, which are difficult to simulate by SWAT program. Therefore, in this study the SWAPP (SWAT/APEX Programs) program was developed to facilitate the simultaneous use of these two models. The SWAT (version 2000) and APEX (version 2110) models are applied using the SWAPP program to the upper North Bosque River (UNBR) watershed located in central Texas. Flow and loadings (sediment and nutrients) from various land uses, such as cropland and pasture, are simulated by APEX and then are routed by SWAT within the SWAPP program. SWAT alone (SWAT-A) and combined SWAT and APEX models within SWAPP program are calibrated and verified against historical monitoring data collected within UNBR watershed. The UNBR watershed is simulated from 1988 through 1999 model output is calibrated for flow, sediment, and nutrients measured at the outlet of UNBR watershed for the period of January 1994 through June 1995 and verified for the period of July 1995 to July 1999 The results of this study show that output from SWAT-A and SWAPP are similarly close to measured values, which indicates that the simulated field conditions by APEX can be routed by SWAT at the watershed level using the SWAPP program.

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