Integrating hydrogeochemical and geophysical data for testing a finite volume based numerical model for saltwater intrusion

In this paper, hydrogeological and geophysical data are used to validate a numerical model developed to predict seawater intrusion into coastal aquife rs. The cell-centered finite volume method is adopted here to solve the set of coupled partial differential equations describing the motion of saltwat er and freshwater separated by a sharp interface. These equations are based on the Dupuit approximation and are obtained from integration of 3D flow e quations for fresh and salt water zones over the vertical dimension. In ord er to have flexibility upon complex configurations domain, non structured g rid meshing is utilized. To approximate the diffusion fluxes, Green-Gauss t ype reconstruction, based on diamond-cell and least squares interpolation, is performed. The model is first validated using academic test case studies with known closed form solutions. The mathematical model has been calibrat ed using hydrogeochemical and geophysical data. The geophysical method appl ied in this study has been a frequency domain electromagnetic method. In th is method the apparent electrical conductivity is measured by induction usi ng two separate hand-held transmitter and receiver coils. During the operat ion the transmitter coil is energized by a low frequency alternating curren t that radiates an electromagnetic field and the receiver coil detects the resulting field. Taking into account the relationship between the bulk cond uctivity of the subsoil and the conductivity of groundwater, EM soundings h ave been interpreted to provide complementary information to hydrogeochemic al data to outline the fresh-saltwater interface. This methodology has been applied to the case of saltwater intrusion into the Llobregat delta aquife r, near Barcelona, Spain.