Riverbank filtration (RBF) is a widely applied technique of managed aquifer recharge (MAR). It utilizes the river-groundwater interface and can enhance groundwater quantity and quality. However, a profound understanding of hydraulic interactions and biogeochemical processes is required for a successful and sustainable implementation of this method. Such an approach includes local and regional monitoring strategies to understand recharge efficiency and water quality benefits, which may vary due to, e.g., river flow fluctuations, possible upstream input of pollutants, and aquifer heterogeneity.

In this study, we investigated river water-groundwater mixing and groundwater residence times, aiming to improve knowledge on aquifer recharge dynamics at the RBF site Kępa Bogumiłowicka, an important regional drinking water provider near Tarnów, Poland. We coupled environmental tracers (stable water isotopes, chloride concentration, water temperature and specific electrical conductance) with high-resolution hydrological, meteorological and groundwater abstraction records. Results show that RBF is the predominant recharge mechanism of the local aquifer, where bank filtrate contributes more than 90% to the yield of the seven production wells near the riverbank.

With our case study as an example, we propose a practical and transferable methodology for efficient RBF monitoring and management. The suggested workflow implements monitoring of multiple tracers and the application of ensemble end-member mixing analysis (EEMMA) covering at least one hydrological year. Such a framework allows robust and cost-effective recharge-source assessment. It determines the quantitative status of abstracted groundwater and facilitates proactive responses to upstream pollution events and/or rapid hydrological shifts, which is crucial for resilient and sustainable water resource management.