The Use of the SWAT Model to Optimize Water Yield from Brush Control in the Upper Guadalupe River Basin

The encroachment of wooded species in herbaceous dominated rangelands has caused pronounced ecological change. Plot scale studies indicate a decrease in available water due to increased evapo-transpiration from wooded species. When these effects are modeled over an entire basin, significant hydrologic impacts are observed. The results of these studies have encouraged the implementation of state subsidized brush control in several watersheds in Texas. To effectively realize such a plan, effort must be made to determine what hydrologic characteristics define optimal sites for brush control to obtain the greatest (if any) increase in water yield from removal. The influence of soil depth, slope, and brush cover were assessed using the Geographic Information Systems (GIS) version of the Soil and Water Assessment Tool (SWAT) for the Guadalupe River basin. The SWAT model was used to simulate the removal of brush species from locations that were characterized by combinations of: 1. shallow soil layers to enhance infiltration to underlying fractured substrate, 2. moderate slopes to increase runoff to stream channels, and 3. locations that are covered by the thickest extents of wooded cover. Characteristics for optimal sites were chosen by the increase in water yield for each unit area of treatment.