A model of ground water discharge from an unconfined coastal aquifer

A two-dimensional, field scale, finite-element ground water model was devel oped to simulate the ground water discharge process within an unconfined co astal aquifer, Model development was based on the density dependent fluid f low approach with water table and dynamic tidal boundary conditions, The pe rformance of the model was compared against data collected from the Columbi a Aquifer on the eastern shore of Virginia. The dynamic tidal boundary cond itions were necessary to reproduce the surficial mixing zone observed withi n the ground water intertidal zone of the aquifer, The model was able to re produce field data on the movement of the near-shore water table, ground wa ter salt concentrations, and ground water discharge rates and patterns. The model was not able to replicate the short-term fluctuation in salt concent ration observed within the surficial mixing zone, The inability to account for the wave action of the tides,within the intertidal zone is believed to be responsible for this difficulty. The development of the model provided a new method to investigate ground water discharge to coastal systems.