Effects of grid resolution on regional modelled groundwater salinity and salt fluxes to surface water

Coastal fresh groundwaters face growing threats from rising withdrawals and climate change, with salinization of surface and groundwater as notable impacts. Recent developments in parallel variable-density modelling enable studying these threats at unexplored resolutions and extents. To improve the understanding of ground- and surface water salinization processes we designed an experiment to measure how spatial resolution affects both groundwater salinity distribution and salt loads to surface waters. An existing parallelized coupled variable-density groundwater flow and salt transport (VD-GWT) model is applied to a region in the Netherlands whereby the surface water drainage network is parameterized at grid resolutions between 10 and 250 m. The results show a strong dependency between resolution and the salinity distribution in shallow groundwater while simulated salt loads are affected by imperfect flux scaling. The computational resources needed for this test suggest that regional high-resolution VD-GWT models are feasible using HPC environments, albeit not practical.