000005337 001__ 5337
000005337 005__ 20210527082415.0
000005337 037__ $$aSEMIN-2021-0008
000005337 100__ $$aVan Camp, M.
000005337 245__ $$aThe weight of water, Investigating ground water content by using terrestrial gravity measurements
000005337 260__ $$c2021
000005337 269__ $$c2021-05-10
000005337 520__ $$aFor the 20 last years, terrestrial and satellite gravity measurements have reached such a precision that they allow for the identification of the signatures from water storage fluctuations. In particular, hydrogeological effects induce significant time-correlated signature in the gravity time series. Gravity response to rainfall is a complex function of the local geologic and climatic conditions, e.g., rock porosity, vegetation, evaporation, and runoff rates. The gravity signal combines contributions from many geophysical processes, source separation being a major challenge. At the local scale and short-term, the associated gravimetric signatures often exceed the tectonic and GIA effects, and monitoring gravity changes is a source of information on local groundwater mass balance and contributes to model calibrations. The main characteristics of the aquifer can then be inferred by combining continuous gravity, geophysical and hydrogeological measurements. In Membach, Belgium, a superconducting gravimeter has monitored gravity continuously for more than 25 years. This long time series, together with 300 repeated absolute gravity measurements and environmental monitoring, has provided valuable information on the instrumental, metrological, hydrogeological and geophysical points of view. This has allowed separating the signal sources and monitoring partial saturation dynamics, convective precipitation and evapotranspiration at a scale of up to 1 km², for signals smaller than 1 nm/s², equivalent to 2.5 mm of water.  Based on this experience, another superconducting gravimeter was installed in 2014 in the karst zone of Rochefort, Belgium. In a karst area, where the vadose zone is usually thicker than in other contexts; combining gravity measurements at the surface and inside accessible caves is a way to separate the contribution from the unsaturated zone lying between the two instruments, from the saturated zone underneath the cave, and the common-mode effects from the atmosphere or other regional processes.  Those experiments contribute to the assessment of the terrestrial hydrological cycle, which is a major challenge of the geosciences associated with key societal issues: availability of freshwater, mitigation of flood hazards, or measurement of evapotranspiration.
000005337 594__ $$aNO
000005337 6531_ $$aTime-varying gravity
000005337 6531_ $$aSuperconducting gravimeter
000005337 6531_ $$aMembach
000005337 6531_ $$aRochefort
000005337 6531_ $$aHydrogeodesy
000005337 6531_ $$aEvapotranspiration
000005337 773__ $$tIGN & IPGP Paris, France
000005337 8560_ $$fmichel.vancamp@observatoire.be
000005337 980__ $$aCTALKCONT