LOCALLY INVERSED SALINITY DISTRIBUTION IN A SLOPING-BEACH CROSS-SECTION

Most studies on the seawater-groundwater interactions focus on large-scale (kilometers) solute transport. The well-known conclusion is the presence of a saltwater wedge below a seaward moving freshwater. This paper focused on small–scale solute transport in a sloping-beach. Transient hydraulics and solute transport were investigated numerically using a novel dimensionless formulation and the variably-saturated model for density-and-viscosity-dependent flows, MARUN [Boufadel et al., J. of Contaminant Hydrology, v37, 1-20, 1999]. Experimental, analytical and numerical results showed that water in the reach enters the subsurface at a downward angle and exits it at an upward angle. The salinity distribution in beaches can be inverted due to tides with saltwater from sea that overtops the freshwater lens, i.e., the salt water is above the freshwater in the cross of the beach. This small-scale salinity distribution is a reverse of the large-scale one. The conditions under which the significant inverted salinity distribution occurs were discussed by means of model parameters such as the sloping angle, the beach permeability, tidal frequency and amplitude, and inland freshwater recharge rate etc.. We found that the smaller the sloping angle or the permeability of the beach soil, the more significant the reversed salinity distribution.