Modeling of the complex karstic system in Saint-Chaptes (Gard, France): A tool for the synthesis of geological and hydrogeological data

Numerous software packages allow the efficient modeling of the hydrodynamic behaviour of aquifers in continuous media. To study pressure transfer in d iscontinuous media like karsts, the black-box models are restrictive and th e models that consider discrete conduit networks are unsuitable for reservo ir scale. We show that the utilization of a continuous media model can lead to useful results, even in the case of complex systems, but needs to be ad apted to karst specificity. The problem is approached by studying a hydroge ological system located in the Mediterranean Languedoc region: the S-t-Chap tes basin. This system consists of three superposed aquifers included in fo ur different stratigraphic series. The main aquifer is a karst formation in contact with two other karst formations that belong to different hydrogeol ogic systems. Considering geological data in addition to hydrological data and with the hypothesis of a relative homogenization of the karst's hydraul ic behaviour on a large spatial scale for daily to monthly increments, the model that takes into account the relations with the other aquifers allows (i) a preliminary identification of the main heterogeneities inside the res ervoir; (ii) the location of barriers and low-permeability zones that isola te some parts of the aquifer; (iii) the observation of a curious behaviour of the piezometric levels in the confined zones of the aquifer; and (iv) th e characterization of the exchanges with the other low-volume but existing aquifers.