Saltwater Intrusion for Finite Peclet Numbers in Random Permeability Aquifers

The paper deals with the definition of the interface between saltwater and freshwater in an heterogeneous media with prescribed statistical properties of hydraulic log-conductivity. In many coastal aquifers intrusion of seawater is the more relevant constraint imposed on groundwater utilization, making useless the pumping wells drilled for the agricultural or human consumption. Here, to assess in a probabilistic manner the saltwater-freshwater interface position, the combined effects of the porous media hydraulic log-conductivity heterogeneity and the pore-scale diffusion process are investigated. To reach this goal we solve numerically the density dependent flow and transport problem via a Mixed Hybrid Finite Element – Finite Volume approach coupled with the Monte Carlo technique to taking into account the heterogeneity spatial variations. The numerical simulations are developed in a vertical plane of a confined aquifer with a limited degree of heterogeneity. The effects due to the non perfect layering and a finite Peclet number are investigated and the results in term of concentration profiles compared with the interface positions obtained from the closed form solution given by Dagan and Zeitoun [3]. From the experiments we conclude that, in the investigated range, the uncertainty in the interface position is almost well accomplished by the closed form solution, but also that, for finite Peclet values, the pore-scale diffusion may give effects comparable with those due to the spatially variable hydraulic conductivity.