Modeling Sediment Yield in the Sink Creek and Purgatory Creek Watersheds Near San Marcos, Texas
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Central Texas, along the Balcones escarpment, experiences high-magnitude precipitation events that have the ability to generate large amounts of runoff. In the past, such events have led to significant urban flooding and have devastated entire communities. In an effort to lessen the severity of such flood events, the city of San Marcos, Texas, with the National Resource Conservation Service, constructed five flood control dams. These dams, located in the headwaters of the San Marcos River, as well as one of its tributaries, have been successful in protecting the city from catastrophic flood events. Due to an increase in urbanization in the region, rainfall runoff modeling has been suggested in order to better understand the hydrologic processes occurring in these watersheds. This study used the Soil and Water Assessment Tool (SWAT) to model and compare sediment yield for Sink Creek and Purgatory Creek watersheds. This comparison allows a better understanding of which variables are more important to soil erosion. Results show that Sink Creek watershed has a higher total sediment yield (t), while Purgatory Creek watershed has a higher specific sediment yield (t/ha). Soil type and land use were found to be the best predictors of erosion. Results also showed that the top 25 percent of the highest total monthly precipitation produced greater than 55 percent of the overall sediment yield during the period of observation.