Combining Seismology, Hydrogeology and Climatology for Monitoring Karstic Groundwater Reservoirs.

Due to their heterogeneity and inaccessibility, karst aquifers are poorly understood along with their functioning, complex structure and behavior in response to flood events. Conventional methods such as piezometers or other underground equipment give only punctual observations that are not very representative of the functioning of the aquifer at the scale of the catchment basin, nor show spatio-temporal variation that occur along the karst network. The objective of this work is to image the flow of water over time from rainfall to the aquifer outlet in a target catchment basin located in the Jura Mountains near Besançon (Eastern France, Fourbanne site of the 'Jurassic Karst' observatory), which hosts a karstic aquifer monitored since 2014 (Cholet et al. 2017). The approach consists in analyzing jointly seismological, hydrogeological and atmospheric data recorded on the aquifer. The instrumentation comprises 2 permanent seismometers, 2 Conductivity Temperature and Pressure (CTD) probes and 1 rain gauge, which will be completed by 65 seismic nodes, 30 rain gauges and 1 additional CTD for an acquisition period of 4 months. We observe that underground hydrological processes occurring in the aquifer, such as water flow or sediment transport, can be precisely monitored using data from one seismometer installed inside the karst conduit. Furthermore, noise cross-correlation analysis will be carried out to detect seismic velocity variations in the medium induced by fluid saturation changes (Froment, 2011). Several studies have demonstrated that these methods can detect changes in saturation in underground aquifers (Lecocq et al. 2017; Voisin et al., 2017). Accordingly, velocity variation will be correlated with flow velocity, soil water content or even permeability, based on measurements of the volume of water entering the basin and circulating in the karstic network obtained from data collected from the CTDs and rain gauges.

 

References:

FROMENT B., 2011 – Utilisation du bruit sismique ambiant dans le suivi temporel de structures géologiques. [Grenoble]: École doctorale terre, univers, environnement.

LECOCQ, T., LONGUEVERNE, L., PEDERSEN, H.A., 2017 – Monitoring ground water storage at mesoscale using seismic noise: 30 years of continuous observation and thermo-elastic and hydrological modeling. Sci Rep 7, 14241 (2017). https://doi.org/10.1038/s41598-017-14468-9

VOISIN, C., GUZMAN, M., REFLOCH, A., TARUSELLI, M. and GARAMBOIS, S., 2017 – Groundwater Monitoring with Passive Seismic Interferometry. Journal of Water Resource and Protection, 9, 1414-1427. doi: 10.4236/jwarp.2017.912091.

CHOLET, C., CHARLIER, J.-B., MOUSSA, R., STEINMANN, M., DENIMAL, S., 2017 – Assessing lateral flows and solute transport during floods in a conduit-flow-dominated karst system using the inverse problem for the advection–diffusion equation. Hydrology and Earth System Sciences 21, 3635–3653. https://doi.org/10.5194/hess-21-3635-2017