Effets du lissage de la nappe lié à la résolution topographique sur la simulation des écoulements régionaux des eaux souterraines

The assessment and management of groundwater often depend on large regional numerical models that predict hydrological stresses, such as those caused by climate change and resource exploitation. While regional and continental-scale models have been developed to evaluate these impacts, they typically use coarse grid cells that smooth land surface topography. This study investigates the impact of topography-controlled water table smoothing on simulated groundwater discharge to streams (baseflow) and associated groundwater age. A simplified 2D cross-sectional model of a topographically driven regional aquifer system was developed, under the assumption that the water table is a replica of the land surface topography. Scenarios with varying topography, derived from resampling digital elevation model (DEM) resolutions ranging from 30 to 10,000 m, were analyzed using a consistent, high-resolution numerical hydrogeological model mesh. Results show that baseflow rates decrease significantly as resolution declines, primarily due to reduced hydraulic gradients, with a flux dif- ference of an order of magnitude simulated between resolutions of 30 and 1000 m. Although shallow groundwater flows in more permeable aquifer layers are significantly affected, deeper regional flow remains stable across all scenarios. Regional groundwater flow paths and associated residence times are less sensitive to changes in resolution, particularly at depths greater than 50 m in the model used. The study thus demonstrates that low-resolution models need to overestimate hydraulic conductivity during calibration to accurately match fluxes to streams. This study highlights the critical importance of care- fully considering topographic resolution in regional models to ensure representative predictions of streamflow driven by subsurface–surface interactions.