High‐Resolution Monitoring of Controlled Water Table Variations From Dense Seismic‐Noise Acquisitions

International audienceWater-resource management has become a major global issue in a world threatened by climate change. High-resolution geophysical methods may be of valuable help in monitoring the water masses, both in space and time. Passive seismic interferometry takes advantage of ambient seismic noise to recover the variations in seismic wave velocity induced by changes in groundwater. We present hereafter the time and space monitoring of an hydraulic dome artificially formed to prevent biological and chemical pollutants from entering the exploitation field of Crépieux-Charmy (Lyon, France). We use a dense seismic network to passively monitor the water table changes induced by infilling of an infiltration basin at the water supply facility for the two million inhabitants of the Lyon Metropolis (France). We assess the hourly seismic velocity variations over 19 days, during which two filling and drainage cycles were performed. The use of a dense three-component seismic network allows fine characterization of the seismic wavefield, and offers the possibility to include the analysis of 4,851 raypaths in a robust inversion algorithm based on ray theory. The velocity variations are mapped with high resolution. They are directly related to the water table variations and to residual water saturation changes within the unsaturated zone. This seismic experiment highlights the three-dimensional (3D) implementation and evolution of a hydraulic dome under the infiltration basin. This dynamic information helps in the understanding and modeling of water flows between the water table and a river, which represents a fundamental issue for discussions on the effectiveness of the barrie