Geoelectrical Monitoring

Infiltration monitoring

Since Electrical Resistivity Tomography (ERT) is able to image ground resistivity variations and that these variations are strongly dependent on the water content and its conductivity, electrical resistivity tomography (ERT) is a suitable way to image the water distribution within the epikarst. ERT monitoring also allows retrieving information on water dynamics in karst. A supplementary method is a sprinkling experiment already applied in some karst systems to infer the water dynamics, especially the water retention in the unsaturated zone and the major flowpaths. Self-potential (SP) measures are also of interest as water infiltration in the ground is responsible for measurable self-potential (SP) signals. This allows detecting preferential infiltration pathways. Finally, the water dynamics is also investigated through environmental monitoring above and within caves, among other through tracers monitoring in cave drips.

Monitoring changes in groundwater content and flows in the epikarst

For a better understanding of the infiltration processes within the epikarst, a continuous monitoring of spatial and temporal changes in the water content within the epikarst is necessary. An ERT monitoring system is installed to image, at least on a daily basis, the spatial variability of resistivities due to the complex geometry of the epikarst. This system is complemented by a network of buried temperature sensors to correct thermal effects on resistivities. Additionally, SP signals will be measured to obtain information about water flows in the epikarst through the electrokinetic effect. The ground moisture is also monitored locally through a network of time domain reflectometry (TDR) and water conductivity probes. Discharge, temperature and conductivity of the water that percolate thought the epikarst are monitored at different sites using flow recorders inside the cave.

These repeated measurements are used to constrain and interpret the results of the ERT images in terms of ground water content. Together with onsite precipitation data and infiltration monitoring within the cave, this should lead to a better understanding of infiltration dynamics and water redistribution within the epikarst. We are also relying on the available long series of water flow being recorded through stalactites in the RCL as well as local meteorological data.

Additionally, we plan to conduct fluorescent tracer tests thought the surface and the cave passages and to image with ERT the effects of sprinkling of a known amount of water of controlled conductivity (salt tracer test) to provide insights into the retention zones and preferential flowpaths in the epikarst. These experiments shall be conducted in different moisture conditions in the epikarst.

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