Impacts of evaporation on subsurface flow and salt accumulation in a tidally influenced beach

Abstract

We coupled a mass-transfer formulation of evaporation to the density-dependent variably saturated finite element model MARUN to predict the salinity under realistic conditions in a beach in the Gulf of Mexico. The results showed that evaporation almost doubled the pore water salt concentration in the intertidal zone in comparison to the case with no evaporation. The results also showed that for the relatively wet atmospheric conditions, the maximum evaporation did not occur from the supratidal zone, rather from the intertidal zone, and it was due to the difference in moisture between pore water and atmosphere. The highest salinity occurred during the spring tide period, and extended into the neap tide period. When the atmospheric condition was assumed to be constant and conducive to large evaporation (high temperature and low air humidity), the maximum salinity region shifted to the supratidal zone and persisted there due to low mixing. The maximum salinity value in the intertidal zone for this case was not larger than that of the variable atmospheric condition case. However, the maximum was more landward than the (more realistic) variable atmospheric condition case, which suggests that accurate characterization of pore water salinity in tidally influenced beaches requires accurate knowledge of atmospheric conditions in addition to beach and hydraulic properties. The constant atmospheric condition simulations suggest that antecedent extreme conditions greatly affect the salinity in the supratidal zone but they are dampened in the intertidal zone.