Hydraulic interactions between fractures and bedding planes in a carbonate aquifer studied by means of experimentally induced water-table fluctuations (Coaraze experimental site, southeastern France)

• Published in: Hydrogeology journal Vol. 17; no. 7; pp. 1607 - 1616
• Main Authors: Charmoille, A, Binet, S, Bertrand, C, Guglielmi, Y, Mudry, J
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Berlin/Heidelberg : Springer-Verlag 01-11-2009; Springer-Verlag; Springer Nature B.V; Springer Verlag
• Subjects: Aquatic Pollution; Aquifers; Carbon dioxide; carbonate rocks; Conceptual models; Earth and Environmental Science; Earth Sciences; Environmental Sciences; Fluctuations; Fractured rocks; Geochemistry; Geology; Geophysics/Geodesy; Global Changes; Groundwater; Hydraulic gradient; Hydraulic properties; hydrochemistry; Hydrogeochemistry; Hydrogeology; Hydrology; Hydrology/Water Resources; Karst; Measurement techniques; Mineralization; Permeability; Piezometric head; Pressure; Sciences of the Universe; Unsaturated zone; Waste Water Technology; Water flow; Water Management; Water Pollution Control; Water Quality/Water Pollution; Water springs; Water table; France; Fractured rocks; Hydrogeochemistry; Unsaturated zone; Karst; Hydrochemistry; Carbonate rocks; France; Conceptual models; Hydraulic properties; hydraulic properties; hydrogeochemistry; fractured rocks
• ISSN: 1431-2174; 1435-0157
• DOI: 10.1007/s10040-009-0470-y

In aquifers with variable permeabilities, the water exchanges between high- and low-permeability regions are controlled by the hydraulic head gradient. Past studies have addressed this problem mainly considering steady-state hydraulic conditions. To study such exchanges during water-table fluctuations, a spring in southeastern France was equipped with a water-gate that creates 10-m artificial fluctuations of the water table. The water exchanges are discussed with respect to hydrochemical and pressure measurements in the groundwater. With successive water-table fluctuations the mineralization and pH decrease, but the bicarbonate content increases in response to carbon dioxide dissolution. At this scale of single fractures and surroundings, the hydrochemistry allows water flows from low- or high-permeability discontinuities to be discriminated. During hydraulic head fluctuations, the waters from low- and high-permeability discontinuities become mixed. During water-table rise, the low-permeability matrix contributed to the refilling of the permeable faults and to the mixing of the waters. Dynamic flows in the opposite direction to the hydraulic gradient can expel mineralized water, pushing it towards permeable discontinuities. This mechanism could be the cause of the peak in the mineralization recorded in some karst springs at the start of flood events.