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The simulation of coupled flow and transport processes in unsaturated porous media over catchment areas extending for several tens of square kilometers may require extensive computational resources, thereby constraining the practical applicability of three-dimensional hydrogeological models. To enhance the efficiency of three-dimensional models, this study investigates a dual meshes approach, comprising a coarse mesh adequately refined for flow simulation and a fine, adaptive mesh dedicated to transport computations in order to accurately capture tracer dispersion. The transport mesh is subjected to dynamic refinement based on localized normalized concentration gradients. The methodology is firstly validated through a comprehensive one-dimensional study and subsequently applied to a realistic three-dimensional scenario that simulates tracer injection into both saturated and unsaturated zones. The outcomes highlight the efficiency of this approach, indicating that computational time can be reduced by up to two orders of magnitude in the employed configurations, while still maintaining accuracy comparable to the standard method.
Horgue et al. (Mon,) studied this question.