134 A new concept of karst development based on hydrogeology and geophysics The spatial distribution of karst conduits is only partially known, generally at locations where they intersect the land surface (e.g., sinkholes and springs) or are intercepted by boreholes. Even when accessible portions of a karst system can be mapped by speleologists, the explored conduits represent only a small fraction of the full drainage network. Research at the Hydrogeological Experimental Site (HES) of Poitiers University (France), focuses on a limestone aquifer located at depths of approximately 35–130 m (supra-Toarcian aquifer). The site comprises 45 boreholes over an area of 15 ha, including 28 boreholes concentrated within a 210 × 210 m square (Fig. 1). Karst features at the site occur preferentially within four lithostratigraphic units, each sub-horizontal, 2–5 m thick, and located at depths of ~30, 50, 85, and 115 m below ground surface (Mari and Porel, 2008; Mari et al., 2009; Mari and Porel, 2024). A 3D seismic survey was conducted at the HES in 2004. Complementary to the surface seismic data, full acoustic logs were acquired in 6 boreholes: C1, MP5, MP6, M08, and M09. Cross-analysis of the 3D seismic model and borehole logs revealed a strong relationship between low-velocity seismic zones and inflow/outflow horizons associated with high hydraulic conductivity (Mari and Porel, 2008). Finally, using tracer-test data from 50 inter-well tests performed within the seismic survey area, together with borehole flowmeter logs, Bodin et al. (2022) demonstrated the feasibility of delineating discrete karst conduit networks. Figure 1 Location of the boreholes at the HES in Poitiers, France.
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