Frozen Ground Induces Seawater Retreat in Coastal Unconfined Aquifers

Abstract While seawater intrusion (SWI) in coastal aquifers has been extensively investigated, most studies focused on unfrozen conditions. In many cold regions, frozen ground is common, yet its impact on SWI remains poorly understood. Here, we demonstrate that the formation of frozen ground alters salinity distribution in coastal unconfined aquifers, based on laboratory experiments and numerical simulations. Under steady‐state conditions with subzero ground temperature, frozen ground creates a confined flow path between itself and the saltwater wedge. This configuration accelerates terrestrial groundwater flow and induces a pronounced seaward retreat of the saltwater wedge. Moreover, lower ground surface and groundwater temperatures enhance this effect by promoting frozen ground formation. These findings have important implications for understanding salinity dynamics in coastal cold‐region aquifers with varying frozen ground.