Saltwater Intrusion and Recirculation of Seawater at a Coastal Boundary

Abstract

Numerical experiments were performed to investigate saltwater intrusion and recirculation of seawater at a coastal boundary. A field-scale two-dimensional cross section was simulated in which freshwater inflow occurred at an upgradient boundary, and saltwater inflow, freshwater outflow, and recirculated seawater outflow occurred at a downgradient boundary. The upgradient boundary is a specified-flux boundary with a zero (i.e., freshwater) concentration, and the downgradient boundary is a specified-head boundary with a specified (i.e., saltwater) concentration. This problem was solved numerically using SEAWAT for two conditions; i.e., first for the uncoupled condition in which the fluid density is constant, and thus, the flow and transport equations are uncoupled in a constant-density flowfield, and then for the coupled condition in which the fluid density is a function of the concentration of total dissolved solids, and thus, the flow and transport equations are coupled in a variable-density flowfield. Equivalent freshwater heads are specified at the downstream boundary for both conditions to account for density differences between freshwater and saltwater at the downstream boundary. For both conditions, it was determined that saltwater intrusion and seawater recirculation are decreased significantly as the dimensionless ratio of the freshwater inflow relative to the density-driven buoyancy flux (