Saltwater intrusion in Denmark

The studies investigating saltwater intrusion in Denmark have been reviewed to identify the main characteristics and features that have an impact on coastal aquifers interacting with the sea. Traditionally, in regions with wet climate, saltwater intrusion is not appointed as a frequent problem and it is more commonly linked to areas affected by water scarcity. Nevertheless, multiple factors that can induce the salinization of coastal aquifers have been found for Denmark such as the presence of coastal drained lowlands with the water table below the sea level or karstic features and buried valleys in carbonate and detrital systems respectively that can act as preferential flow paths for saline water. Eustatic changes have been also played an important role in the salinization of aquifers, in deep aquifers saline ancient connate water can be identified and in small islands, a delicate equilibrium of freshwater lenses is generated over saline water. As the water supply in this country depends almost exclusively on groundwater, saltwater intrusion can jeopardize fresh groundwater resources in coastal areas. An overview of the cases already studied, questions about the magnitude of these issues and the future perspectives with climate changes are discussed to put into context what is already known and what are the next challenges.