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This report documents recent updates and recalibration of the MODFLOW groundwater model of the San Antonio segment of the Edwards Aquifer. Conceptual and structural updates include addition of spring outflows and hydrologic flow barriers, removal of explicit conduits, elimination of the Barton Springs segment, new top and bottom layer elevations, and use of explicit well locations to represent pumping. The updated model was calibrated to match observed water levels and spring flows at the end of each month for the period of January 2001 through December 2011. Calibration errors in the updated model met the goals set prior to beginning the update and calibration process. As a validation test, the model was run forward to include years 2012 through 2015, which were not used in the calibration; the model reasonably matched observations for those years, although the overall errors were somewhat greater than for the period it was calibrated to. The model also reasonably matched observations for a drought-of-record simulation of years 1947 through 1958. Uncertainty in recharge is believed to be a significant factor contributing to model error.
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