Hydraulic characterization and identification of flow-bearing structures based on multi-scale investigations applied to the Lez karst aquifer

Abstract

Study Region: The Lez aquifer is a Mediterranean karst system located in southern France, which supplies groundwater to the Montpellier urban area. Study Focus: Multi-scale hydrodynamic investigations were carried out in a fractured and karstic aquifer in order to identify the flow-bearing structures and evaluate their hydraulic properties. The study is based on an extensive dataset developed from several hydraulic tests, performed at different spatial and temporal scales. The scales ranged spatially from a few meters to more than 15 km and temporally from a few minutes to a few months. New Hydrological Insights for the Region: The data analysis shows that the hydraulic connectivity at both local and regional scales is mainly due to sub-horizontal flow-bearing structures, in which a conduit network has developed. This structure appears mainly to be located at the interface between two stratigraphic units, at the transition between Jurassic and Cretaceous limestones (Kimmeridgian-Berriasian interface). At the regional scale, this flow-bearing structure plays a major role in large-scale connectivity since a compartmentalization of the Lez aquifer appears where the continuity of this structure disappears. The hydraulic properties estimated appear to be strongly dependent on the investigated geological structures and on the different hydrogeological methods used for the borehole, local and regional scale of investigations. Keywords: Hydraulic tests, Multi-scale analysis, Heterogeneity scale, Fractured and karstic carbonate rocks, Karstified bedding-planes