Spatial and Temporal Variability of Water Storage in Dolomite Karst from Gravity Measurements

Friday, 19 December 2014
Cédric Champollion, Benjamin Fores, Jean Chery, Nicolas Le Moigne, Ouail Khairoun, Erik Doerflinger and Philippe Vernant, Laboratoire Geosciences, UMR 5243, Montpellier, France
Karstic hydrosystems are highly nonlinear and heterogeneous but they represent one of the main water resources in the Mediterranean area. Neither local measurements in boreholes nor analysis at the spring can take into account the variability of the water storage. Since few years, ground-based gravity measurements allow the monitoring of the water storage in heterogeneous hydrosystems at intermediate scale between boreholes (local scale) and spring (global scale).From many experiments in the Durzon karstic system in the south of France, we studied the seasonal water storage at different spatial scales. Firstly, all gravity experiments, carried out witha well suited methodology,show significant signals. Surface and depth measurements at small scale (20-50 m in depth and 20-50 m in surface) shows significant gravity variations. The equivalent water storage variations are interpreted in relation with the subsurface observations: topography, geomorphology and lithology. At larger scale (100m – 5000m), equivalent water storage variations is linked with alteration and karstification.

The main results are the importance of the seasonal water storage in the epikarst and the spatial coherence of the gravity measurements. These experimental studies show the potential impact of the spatially distributed gravity measurements for further hydrological numerical models.