Asymmetric Variation of Ghyben-Herzberg Lens

An asymmetric freshwater lens is shown to exist in a long narrow coastal barrier beach bounded on one side by a salt water lagoon and on the other by the ocean. Field measurements of ground-water specific conductance and water table elevations show the lens to average approximately 17 ft (5 m) in maximum thickness and to be thicker on the side toward the lagoon. The asymmetry is apparently due to an effective mean sea level higher than actual mean sea level on the ocean side which occurs because of tide and wave action on a sloping ocean beach. An approximate analytical model enabling calculation of the asymmetric lens is described which utilizes the Ghyben-Herzberg relation with Dupuit assumptions, and input parameters of permeability, recharge, landmass width, freshwater and seawater densities, and effective lagoon/ocean level difference.