Modelling the hydrologic functions of a karst aquifer under active water management – The Lez spring

A rainfall-discharge model is applied to an aquifer characterized by active groundwater management – the Lez karst aquifer in the South of France. Groundwater is withdrawn by pumping in the main drain, 400 m upstream from the main spring and 48 m below the aquifer overflow level. A reservoir model was developed to characterize the functioning of this aquifer. It is based on a conceptual model of the karst aquifer that takes into account flow through both the saturated zone and the unsaturated infiltration zone. Both rapid and slow flow in the infiltration zone and flow in the saturated zone are modelled. Since pumping withdraws groundwater from the main drain of the saturated zone, modules characterizing various pumping practices are taken into account in the saturated zone reservoir. The model simultaneously simulates spring discharge and water levels in the drain, which characterize the saturated zone of the karst. The groundwater reserves stored in the saturated zone can then be estimated. The model can be used for water management. Since runoff and overflow from the aquifer feeding the Lez River depend on the degree of saturation of the aquifer, the model could be used for the flood management.