1-8 Simulation of karst groundwater dynamics in the Byrds Mill Spring subsurface watershed, Arbuckle-Simpson Aquifer

Session: Advances in Managed Aquifer Recharge

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Authors:

Abstract:

The eastern portion of Arbuckle-Simpson Aquifer (ASA) located in south-central Oklahoma has been designated as an EPA Sole Source aquifer since 1989. It is a karst aquifer and the single source of reliable water for about 200 thousand residents in the area. Maintaining the storage of the aquifer and sustaining the stream flow and spring discharge, especially during extended drought and high-water demand, are critical for sustainable development of the local economy and eco-system. Byrds Mill Spring (BMS) is the most prominent spring of the ASA and the largest spring in Oklahoma. To date, no watershed-scale groundwater model around BMS, with explicit representation of the karst aquifer geology, has been developed to evaluate the impact of enhanced aquifer recharge on the water storage and spring discharge. In this study, the BMS subsurface watershed within the ASA was simulated using both the Dual Continuum (DC) and Discrete Fracture Network (DFN) approaches, enabling the representation of distinct hydraulic properties for faults and fractures relative to the surrounding dolomite rock matrix. To achieve this, MODFLOW model was applied through ModelMuse 5.3 for the hydrological year 2020–2021. The model was calibrated manually and with PEST using hydraulic head and spring discharge data, and then validated for 2021–2022. The results from both the DC and DFN approaches were compared to evaluate the performance of each. Sensitivity analysis identified horizontal hydraulic conductivity, vertical anisotropy, recharge, and river/drain conductances as the most influential parameters in model predictions. Moreover, model results showed groundwater generally flows east, toward Byrds Mill Spring, and south, consistent with previous studies indicating regional groundwater flow from northwest to southeast. The water budget analysis shows BMS contributes ~20% of total groundwater discharge of the spring watershed, indicating its major role as a karst outlet. Rivers show strong interaction with the aquifer, while well withdrawals and evapotranspiration are minor. Rainfall is the secondary recharge source, and the aquifer experienced a net gain in storage during the simulation. Furthermore, several scenarios were developed to evaluate suitable Enhanced Aquifer Recharge methods for the study area, identifying potential recharge zones and their impacts on the aquifer.

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

doi: 10.1130/abs/2025AM-7701

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