Representing Hydrodynamic Dispersion in Saltwater Intrusion Models That Differ in Temporal Resolution

Variable-density groundwater flow models are often used to understand the complex nature of coastal groundwater systems. Hydrodynamic dispersion is a difficult process to represent with a model because of spatially varying hydraulic conductivity and temporally varying hydrologic boundary conditions. Temporal variations in water levels, for example, that occur in the field are often averaged into boundary conditions in a model. Three cross-sectional models were developed to test the response of a simulated saltwater interface to different methods for treating the temporally variability in the ocean boundary condition. Results indicate that if temporal tidal variations in model are averaged, simulated concentrations within the interface can be quite different than for the same model that includes the tidal variations. This observation indicates that for certain aquifers, it may not be appropriate to calibrate a variable-density model at one temporal scale and apply the model to a different temporal scale. KEY TERMS: Hydrodynamic dispersion, saltwater intrusion, saltwater interface