Use of a groundwater model to evaluate groundwater–surface water interaction at a riverbank filtration site: a case study in Binh Dinh, Vietnam

Abstract A comprehensive understanding of groundwater–surface water (GW–SW) interaction is important for sustainable water resource management. Riverbank filtration (RBF) serves as a natural method to enhance groundwater recharge, especially in systems where surface water and groundwater are closely connected. Thus, RBF is a feasible option for water management particularly in regions dealing with water scarcity and overexploitation of groundwater. This study investigated GW–SW interaction at a well-field next to the Dai An River in Phu Cat district, Binh Dinh province, Vietnam, with the primary goal of evaluating the feasibility of RBF for water supply at this site. Using FEFLOW 7 software, numerical modelling was conducted to simulate groundwater flow and estimate groundwater recharge rates from riverbank filtration during wet and dry seasons. The model incorporated key aquifer parameters, including hydraulic conductivity and porosity. Additionally, stable (water) isotope analysis of hydrogen (δ 2 H) and oxygen (δ 18 O) was performed to trace GW–SW interaction. The modelling results demonstrated that approximately 72% of total groundwater recharge came from riverbank filtration, confirming a strong hydraulic connection between the river and the aquifer. Stable isotope analysis revealed seasonality in mixing rates, with the surface water contribution to the aquifer ranging from 2% during the dry season up to 54% during the wet season. The travel time from the riverbank to the nearest abstraction well was estimated to be less than 3 days. These findings contribute to understanding of GW–SW interaction in the region and also offer general guidance for optimizing well placement and sustainable groundwater extraction practices.