Multi‐scale electrical resistivity imaging and long‐term monitoring as a tool for groundwater management

Abstract Extensive pumping, storm floods or sea‐level rise can lead to regional and local‐scale processes of saltwater intrusion into coastal aquifers. Particularly when exacerbated by the impacts of climate change, these processes can threaten freshwater resources and thus drinking water supplies and need to be prevented by investigation and monitoring, for example, with resistivity methods. In this study, we present a multi‐scale resistivity‐based imaging and monitoring concept that integrates regional‐scale airborne electromagnetic data, local‐scale surface electrical resistivity tomography data and borehole‐scale data from permanently installed electrode chains for resolving spatio‐temporal processes of groundwater salinization. Based on two field cases in Northern Germany, it is argued that comprehensive multi‐scale geophysical datasets are required for understanding the complex spatio‐temporal dynamics of groundwater salinization. Particularly long‐term monitoring data are essential for resolving groundwater salinization processes and for differentiating long‐term changes from seasonal effects. The approach complements traditional groundwater monitoring and yields crucial data for the development of density‐driven groundwater flow models to support sustainable coastal aquifer management. If installed at an early stage, such monitoring systems can anticipate threats to sustainable groundwater use and generate valuable time for taking counteractions.