Technical Note: Groundwater flow modeling in coastal aquifers – the influence of submarine groundwater discharge on the position of the saltwater–freshwater interface

Abstract. An investigation of the impact of submarine groundwater discharge on the position of saltwater–freshwater interface is presented in this manuscript. Two conceptualizations were considered and analyzed using both analytic and numerical techniques, for comparison purposes. The first conceptualization assumes that the tip of the saltwater–freshwater interface occurs at the shoreline, and the second conceptualization allows for the tip to extend off-shore. Analytic solutions exist for both conceptualizations, i.e., Strack (1976) for conceptualization 1 and Bakker (2006) for conceptualization 2. Results from both analytic and numeric analysis for the two conceptualizations are presented. Results from the first conceptualization were found to overestimate the inland distance to the interface toe, compared to the second conceptualization, for it ignores the influence of submarine groundwater discharge on the interface location. Moreover, results from the analytic solutions as a whole were found to overestimate the interface location compared to the numerical modeling results, for analytic solutions are based on the sharp interface approximations. Therefore, an empirically derived dispersion factor should be used to correct the analytic solution results so as to compare them with the numerically simulated values. Furthermore, offshore model extents should be incorporated when modeling coastal aquifer systems to include the influence of submarine groundwater discharge on the saltwater–freshwater interface position.