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

Amélie Dausse,Véronique Leonardi,Hervé Jourde

doi:10.1016/j.ejrh.2019.100627

Abstract

Study RegionThe Lez aquifer is a Mediterranean karst system located in southern France, which supplies groundwater to the Montpellier urban area. Study FocusMulti-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 RegionThe 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.

Highlights

Karst aquifers, which are generally very productive, constitute important groundwater resources for approximately a quarter of the global population (Ford and Williams, 2007)
The numerous hydraulic tests performed at different spatial scales, from a few meters to more than 15 km, and temporal scales, from a few minutes to a few months, displayed a strong hydraulic property variability of the Lez karst aquifer
Pumping tests may be comparable to high-frequency hydraulic periodic tests, which appear more sensitive to local heterogeneity (Cardiff et al, 2013; Guiltinan and Becker, 2015) and to the main flow path network composed of highly conductive features (Fischer et al, 2018b)

Summary

Introduction

Karst aquifers, which are generally very productive, constitute important groundwater resources for approximately a quarter of the global population (Ford and Williams, 2007). Flow channeling generally occurs at fracture and fracture-network scales (de Dreuzy et al, 2012) but this process may be stronger in karstic reservoirs (Worthington and Ford, 1995). This behavior may be enhanced by the presence of complex networks of enlarged fractures due to wall dissolution, and to the development of karst conduits over several kilometers (Palmer, 1991; Worthington, 1999).

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