39-10 SIMULATING FOCUSED AND DIFFUSE RECHARGE IN THE KARSTIC WATERSHEDS OF FRIO & DRY FRIO RIVERS AND CIBOLO & DRY COMAL CREEKS IN THE EDWARDS AQUIFER REGION, TEXAS

Session: Understanding Karst Hydrology and Karst Aquifers Using Innovative Tracers and Other Technologies

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Reliable assessment of groundwater recharge in watersheds with complex karst features is critical for the development of long-term sustainable land and water resources management plans. In this context, numerical models such as Soil and Water Assessment Tool (SWAT) serve as valuable tools for simulating regional hydrology of the basins and assessing key water budget components. However, the reliability of these models in karstic watersheds, like those of the Edwards and Trinity aquifers in south-central Texas, is influenced by their inherent technical limitations, modeling uncertainties, and reliance on the availability and accuracy of observed input data across the watershed. In this study, we simulated the regional hydrology of two watersheds within the Edwards Aquifer Region with the specific parametrization of SWAT models to represent the characteristics of the karstic watershed and generate groundwater recharge estimates. The results show that while the model performed well in simulating streamflow and groundwater recharge under low-flow conditions, it underestimated streamflow and total groundwater recharge during high precipitation events. Certain parameters displayed high sensitivity in influencing model performance, likely due to the distinctive rapid recharge of precipitation into the aquifer through karst features in the stream channels. These parameters include the lateral delay time and the fraction of transmission losses partitioned to the deep aquifer, in addition to more commonly used calibration parameters such as curve number, groundwater re-evaporation coefficient, hydraulic conductivity, and surface runoff lag coefficient. Moreover, simulated evapotranspiration was generally underestimated in both watersheds compared to the available observations from eddy covariance towers. Additional model improvements are planned to enhance the simulation accuracy. These include incorporating remote sensing evapotranspiration estimates to refine calibration, conducting a comprehensive analysis of basin behavior during high precipitation events, and applying other modeling tools such as SWAT+ to better capture the hydroclimatic complexity of the study area.

Geological Society of America Abstracts with Program. Vol. 57, No. 6, 2025

doi: 10.1130/abs/2025AM-8244

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