Hydrodynamics in a gravel beach and its impact on the Exxon Valdez oil

This paper investigated the interaction of groundwater and seawater in a tidally influenced gravel beach. Field observations of water table, pore water salinity were performed. The two-dimensional finite element model MARUN was used to simulate observed water table and salinity. Based on field observations and model calibrations, a two-layered beach structure was identified which is characterized by a high-permeability surface layer underlain by a low-permeability lower layer. The salt wedge seaward of the low tide line was almost invariant in comparison with the strong fluctuations of the salinity plume in the surface layer of the intertidal zone. The presence of the two layers prevented the presence of a freshwater discharge "tube" between the upper saline plume and salt wedge. This is in contrast with the previous works where freshwater discharge tube was observed. The tide-induced submarine groundwater discharge (SGD) was estimated at 9 m(3) d(-1) m(-1), a large value that is probably due to the large tidal range of similar to 4.8 m and the very permeable surface layer. The freshwater-seawater dynamics revealed here may provide new insights into the complexity, intensity, and time scales of mixing between fresh groundwater and seawater in tidal beaches. The simulated water table of the beach was higher than the interface between the surface layer and the lower layer, which prevented Exxon Valdez oil from penetrating into the lower layer in 1989.