Insights from geophysical methods on the groundwater reserves in the Strengbach mountainous headwater catchment

International audience ; The Strengbach headwater catchment has been monitored since 1986 by the OHGE (Observatoire Hydrogéochimique de l’Environnement) critical zone observatory. Located in the Vosges mountains (northeastern France) with altitudes ranging from 880 m and 1150 m, the 0.8 km² catchment lies on a granitic bedrock. Meteorological and hydrological data are continuously monitored and six boreholes highlight the underground structure down to depths of 50 to 120 m, providing information on the distribution of geological facies.Particularities of this site, such as its relatively thin porous media, compared to sedimentary contexts and its strong topography have encouraged the application of challenging geophysical experiments. Thus, magnetic resonance soundings, which can provide estimates of water contents, were acquired to explore the potential of the method to detect the water content despite the expected low values. Similarly, gravity measurements were acquired to assess whether the method can detect groundwater variations over time despite the strong topography and the poorly known groundwater fluctuations. In addition, seismic refraction tomographies were acquired to provide information on the geometry of hydrofacies. While those experiments were set up separately, we’ll show how they provide complementary insights and could be integrated within a single workflow to solve the hydrological inverse problem at the catchment scale.