EFFECT OF A RIVER FLOOD EVENT ON THE POLLUTANT DISPERSION IN A KARSTIC AQUIFER USING DISCRETE - CONTINUUM APPROACH: A CASE STUDY FROM THE KARST AQUIFER OF THE VAL D’ORLÉANS, FRANCE

A discrete - continuum approach is developed to evaluate the effect of a river flood wave on groundwater heads and consequently on the solute transport within the karst. Darcy’s law and the Brinkman equation were applied in the hosted rock and within conduit, respectively. The karst system of the Val d’Orléans (France) was selected as a case study. The validity of the model was tested using the chloride concentration measurements for two flood events in the Loire River and at Bouillon Spring. The calibration process shows that the optimum permeability values in the hosted rock and in the karst conduits are 5.6E-10 m2 and 1.65E-5 m2, respectively. Good agreement was obtained when the storage coefficient is 0.9 m-1. When the chloride infiltrates from the Loire River into the karst, the simulation shows that the distance penetrated by chloride in the hosted rock is 530 m for a two months flood about 2 m. Such calculation quantifies the volume of vulnerable aquifer surrounding a karstic conduit and highlights the importance of water exchange between conduit and hosted rock.