Numerical simulation of the seasonal salt-freshwater interface: Comparison with electrical resistivity tomography inversion results

•Seasonal changes in seawater intrusion from numerical model and ERT were compared.•Both the numerical model and ERT adequately captured seasonal changes in the SFI.•The use of ERT for delineation of the SFI was validated using numerical method.•The SFI was farther from the west coast in the dry season than in the wet season. Understanding changes in the salt-freshwater interface (SFI) is crucial for predicting seawater intrusion (SI) in coastal aquifers. In this study, we compared electrical resistivity tomography (ERT) data with a numerical model of the SFI to examine seasonal changes in SI in Longkou City, with the goal of reducing the large uncertainty that may be generated when using a single research method and providing a reference for other studies. Therefore, we selected a typical aquifer profile on the west coast of Longkou City, Shandong Province, China, to highlight changes in the SFI. ERT data and aquifer samples were collected during the wet and dry seasons in 2020. An established two-dimensional groundwater flow and solute transport model was then used to simulate the groundwater hydraulic head and the distribution of Cl− concentrations. A dipole and dipole array configuration and the 2D AGI Earth Imager software were used for ERT inversion. The inversion results revealed that the SFI was located approximately 2562 and 2558 m from the west coast in the dry and wet seasons, respectively. Groundwater hydraulic head observations were used to define the hydrogeological parameters in the numerical model. Based on these parameters and observational data, the modelled SFI was located 2330–2830 m and 2350–2580 m from the west coast in the dry and wet seasons, respectively. The ERT inversion and numerical model both indicate that the SFI was closer to the coast in the wet season than in the dry season. The differing SI results obtained from these methods suggest that uncertainty associated with the use of one method alone must be considered in studies regarding water resource management. The findings of this study can be utilised for managing of water resources in coastal areas affected by SI.