3D Structural Modelling and Restoration of a Deformed Alpine Karst Reservoir: Insights into the Groundwater Flows of the Dévoluy Massif (French Alpine Foreland)

Abstract

In foreland fold-thrust belts, tectonically deformed aquifers remain underexplored, largely due to the complex architecture of their hydrogeological reservoirs. This limited understanding prevents the development of sustainable management policies to face the current decline in groundwater availability. In the southwestern Subalpine Chains, we characterised the structure of the folded Senonian karst aquifer of the Dévoluy Massif, which is transected by the Median Dévoluy Thrust. Using surface structural data, we performed an original 3D structural model of the massif. Quantitative analyses of this model indicate a total Senonian package volume of 114 km³, of which 25 km³ lie below the elevation of Gillardes Spring, the main karst discharge. A structural restoration of the base of the Senonian indicates Alpine shortening of ~4.4 km in the southern part of the massif and ~1.2 km in the northern part. The deformation of the karst reservoir into two N-trending synclines, separated by the Median Dévoluy Thrust, is identified as a key control on the northward groundwater drainage pattern, culminating at Gillardes Spring. This 3D structural modelling approach also allowed for identification of suitable areas for the exploration of new deeper resources. Finally, this study highlights the potential of a hydrostructural approach and 3D structural modelling for assessing the hydrogeology in tectonically deformed karst reservoirs.