Comparing dual porosity approach and discrete fracture network for modelling seawater intrusion in fractured porous media

Coastal aquifers are very important as they provide water supply for more than one billion inhabitants around the world. Due to the increased stresses on the coastal aquifers and the anticipated sea level rise from climate change, the risk of seawater intrusion is high. Most of coastal aquifers around the Mediterranean and in the Middle East are comprised of fractured limestone. While numerous studies have been done to investigate flow in coastal aquifers, these studies consider classical flow in un-fractured aquifers. The seawater intrusion in fractured aquifers remains unexplored.

This study focuses on simulating seawater intrusion in fractured porous media using the dual porosity approach (DP). A new numerical model is developed for sweater intrusion with the DP approach, based on advanced finite element schemes. The newly developed model is applied to the common benchmark of Henry’s problem and verified by comparison against a semi-analytical solution and a standard finite element solution obtained with COMSOL Multiphysics. The newly developed model is used to perform a sensitivity analysis for understanding the effect of parameters on the model predictions. The results show that the salinity in the domain is mainly controlled by the mass exchange rate between fractures and porous matrix. The DP approach is compared to the discrete fracture (DF) approach, via an inverse approach procedure. Synthetic observation data are generated with the DF approach and then used to calibrate the DP model. Agreement between the predictions of the DP and DF approaches depends on the fracture density.