QUANTIFYING GROUNDWATER RECHARGE PROCESSES IN THE MOUNTAIN-VALLEY AQUIFER SYSTEM OF A HIGHLY MANAGED WATERSHED

Mountain system recharge (MSR) plays a crucial role in sustaining valley groundwater-fed agricultural ecosystems, yet its contribution to valley-fill aquifers is poorly understood. This study addresses this gap by integrating hydrometric observations and isogeochemical data with numerical modeling and particle tracking to quantify MSR pathways in the Kaweah River Watershed (KRW) in California’s Central Valley. Previous studies suggested that focused mountain-front recharge (MFR) is the primary natural recharge pathway; however, our recent findings indicate that mountain-block recharge (MBR) could be as significant as MFR. We employed an isogeochemical-guided hydrologic modeling approach to constrain recharge estimates from ParFlow.CLM and EcoSLIM simulations in the KRW. Results of 2,500 years of daily spin-up simulations from multiple conceptual models were compared against remotely sensed evapotranspiration, snow-water equivalent, streamflow, groundwater levels, and water age data to choose a model that best represents the hydrologic dynamics of a mountain-valley aquifer system. Our findings revealed that MBR constitute at least 35% of MSR, doubling previous estimates. This study's comprehensive approach not only advances hydrologic science but also offers a valuable decision-support tool for sustainable groundwater management. By integrating diverse data sources and modeling techniques, our work contributes to predicting the influence of water and land management practices in agroecosystems that heavily rely on groundwater. These insights are expected to assist growers and decision-makers in formulating sustainable strategies in the face of climate change and increasing water demands.