Variable density coastal aquifer models with application to an aquifer on Thira Island

The advancement of seawater intrusion in coastal aquifers using three-dimensional variable density transport models is examined. The fluid flow and mass transport processes are considered and the resulting differential equations are solved numerically using finite element method. A constraint based boundary condition regarding chloride concentration is imposed on the seaside boundary. The numerical models are applied to an unconfined aquifer located in the central part of Thira Island (Santorini). Several scenarios are examined corresponding to steady-state and time-dependent conditions. Two potential cases of aquifer replenishment, with natural and artificial recharge are also simulated. The results demonstrate significant dependence of the advancement of seawater intrusion on the initial and boundary conditions prevailing on the seaside boundary of the aquifer. The transition zone predicted by variable density flow and transport models is of considerable width indicating the necessity for modelling using advanced three-dimensional variable density transport models.