Improvement of the solute transfer in a conceptual unsaturated zone scheme: a case study of the Seine River

摘要

For predicting the evolution of solute concentrations in groundwater and testing the impact of remediation policies, a couplingnbetween the agronomical model STICS and the hydrogeological model MODCOU was implemented. When applied to thenSeine River basin, this model accurately represents the temporal evolution of average nitrate concentrations in the aquifer, butnwith large local errors.nWe propose an improvement to the simple unsaturated zone (UZ) scheme NonsatSW used in STICS–MODCOU. Thenmodifications are based on a comparison with the mechanistic model Metis considered as a reference as it solves Richards’nequation. A more realistic saturation profile and a varying percolation rate are integrated in NonsatSW. This new model,nnamed NonsatVG, is assessed by comparing it with NonsatSW and Metis. In an ideal case, NonsatVG generates a solutentransfer and a dispersion closer to that of Metis than of NonsatSW. In real cases, without additional calibration, NonsatVGnand Metis simulate better the average transfer velocities of the observed nitrate profiles.nFurthermore, modifications in NonsatVG give a direct relationship between the depth of the water table and the saturationnprofile. We obtain, therefore, as in Metis, an evolution of the solute transfer velocity depending on the piezometric level.nThese dynamics are not simulated in NonsatSW.nDespite a modified water transfer through the UZ, NonsatVG is also as valid as NonsatSW in the modelling of waterntransfer to the saturated zone.nFinally, an application to the Seine basin shows that solute transfer velocities are lower with NonsatVG than with NonsatSW,nbut are in better agreement with literature. Copyright  2010 John Wiley & Sons, Ltd.