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See detailGravity monitoring of underground flash flood events to study their impact on groundwater recharge and the distribution of karst voids
Watlet, A.; Van Camp, M.; Francis, Olivier UL et al

in Water Resources Research (2020), 56(n/a), 2019026673

Abstract Flash flood events are expected to become increasingly common with the global increases in weather extremes. They are a significant natural hazard that affects karst landscapes, which host large ... [more ▼]

Abstract Flash flood events are expected to become increasingly common with the global increases in weather extremes. They are a significant natural hazard that affects karst landscapes, which host large resources of drinking water worldwide. The role played by underground flood events in the karst aquifer recharge is complex due to the heterogeneity of the basement which remains poorly understood. We present the analysis of 20 in-cave flash flood events affecting the Rochefort karst system (Belgium) using continuous gravity measurements at one single station, and water level sensors installed in caves. Underground flood events typically produce a peak in the gravity signal, due to an increase in the associated mass change. After the flood, the gravity values drop but remain slightly increased compared to before the flood event. Via forward gravity modeling, we demonstrate that this remaining anomaly can be reasonably explained by the infiltration of local rainfall within the karst system rather than by allogenic recharge of the aquifer. Flash floods are mainly restricted to connected voids. This allows us to utilize them as proxies to investigate the distribution of cavities in the karst system. Forward modeling of the gravitational attraction induced by the mapped caves being flooded yields a gravity signal much smaller than the observed one. We conclude that at least 50 more cavities than those previously mapped are required to match the measured anomalies. This presents opportunities for implementing similar approaches in other diverse porous media, using gravity monitoring of hydrological processes (e.g. infiltration fronts, hydrothermalism or tide effects in coastal aquifers) as proxies to characterize underground properties. [less ▲]

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See detailRetrieving hydrological connectivity from empirical causality in karst systems
Delforge, D.; Vanclooster, M.; Van Camp, M. et al

Scientific Conference (2017)

Detailed reference viewed: 54 (4 UL)
See detailContinuous gravimetric monitoring as an integrative tool for exploring hydrological processes in the Lomme Karst System (Belgium)
Watlet, A.; Van Camp, M. J.; Poulain, A. et al

Scientific Conference (2016)

Karst systems are highly heterogeneous which makes their hydrology difficult to understand. Geophysical techniques offer non-invasive and integrative methods that help interpreting such systems as a whole ... [more ▼]

Karst systems are highly heterogeneous which makes their hydrology difficult to understand. Geophysical techniques offer non-invasive and integrative methods that help interpreting such systems as a whole. Among these techniques, gravimetry has been increasingly used in the last decade to characterize the hydrological behavior of complex systems, e.g. karst environments or volcanoes. We present a continuous microgravimetric monitoring of 3 years in the karstic area of Rochefort (Belgium), that shows multiple occurrences of caves and karstic features. The gravity record includes measurements of a GWR superconducting gravimeter, a Micro-g LaCoste gPhone and an absolute FG5 gravimeter. Together with meteorological measurements and a surface/in-cave hydrogeological monitoring, we were able to improve the knowledge of hydrological processes. On the one hand, the data allowed identifying seasonal groundwater content changes in the unsaturated zone of the karst area, most likely to be linked to temporary groundwater storage occurring in the most karstified layers closed to the surface. Combined with additional geological information, modelling of the gravity signal based on the vertical potential of the gravitational attraction was then particularly useful to estimate the seasonal recharge leading to the temporary subsurface groundwater storage. On the other hand, the gravity monitoring of flash floods occurring in deeper layers after intense rainfall events informed on the effective porosity gradient of the limestones. Modelling was then helpful to identify the hydrogeological role played by the cave galleries with respect to the hosting limestones during flash floods. These results are also compared with measurements of an in-cave gravimetric monitoring performed with a gPhone spring gravimeter. An Electrical Resistivity Tomography monitoring is also conducted at site and brings additional information useful to verify the interpretation made with the gravimetric monitoring [less ▲]

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See detailGroundwater Storage in a Karst Vadose Zone Evidenced Using Gravimetric and Surface-to-borehole ERT Monitoring Systems
Watlet, A.; Kaufmann, O.; Francis, Olivier UL et al

Poster (2015, September 06)

Detailed reference viewed: 149 (11 UL)