Groundwater Flow Analysis in a Coastal Aquifer with the Coexistence of Seawater and Freshwater by Using a Non-Hydrostatic Pressure Model

Abstract

The study proposes a new hydrostatic pressure model for flow analysis of a coastal aquifer wherein seawater and freshwater coexist. The numerical model introduces an advection-diffusion equation for salinity and temperature to trace the behaviors of seawater and freshwater in the Navier-Stokes (N-S) solver based on the porous body model (PBM) that considers the characteristics of a coastal aquifer (e.g., particle size, porosity, and shape). Furthermore, the density current is analyzed based on a state equation that determines the properties of water (density and viscosity) based on salinity and temperature. This enables the flow analysis of a coastal aquifer based on non-linear interferences between seawater and freshwater. In order to validate the proposed numerical model, a numerical constant water head permeability test device is set up, and the calculated permeability coefficient of the porous media exhibits a high degree of agreement with the value measured in the experiment. Flow simulations of a coastal aquifer are conducted based on the water level difference and salinity difference between seawater and groundwater. Additionally, hydrodynamic characteristics are analyzed from the water table, flow field, salinity distribution, and maximum penetration distance of the coastal aquifer. Specifically, an in-depth discussion of the diffusion of salinity near the shoreline and the movements of the seawater and freshwater interface is presented, which is largely absent in extant models.