Open AccessTime‐lapse surface to depth gravity measurements on a karst system reveal the dominant role of the epikarst as a water storage entity
Author(s) -
Jacob Thomas,
Chery Jean,
Bayer Roger,
Le Moigne Nicolas,
Boy JeanPaul,
Vernant Philippe,
Boudin Frédéric
Publication year - 2009
Publication title -
geophysical journal international
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.302
H-Index - 168
eISSN - 1365-246X
pISSN - 0956-540X
DOI - 10.1111/j.1365-246x.2009.04118.x
Subject(s) - karst , geology , gravimeter , aquifer , infiltration (hvac) , hydrology (agriculture) , groundwater , specific gravity , bouguer anomaly , gravimetry , soil science , geomorphology , gravity anomaly , mineralogy , geotechnical engineering , geophysics , geography , meteorology , paleontology , casing , oil field , reservoir modeling
SUMMARY In this study we attempt to understand the water storage variations in a karst aquifer on the Larzac Plateau (South of France) using ground‐based gravimetry. Surface to 60 m depth gravity measurements are performed three times a year since 2006 down a pothole, in complement to monthly absolute gravity (AG) measurements at three sites. The time variations of the surface to depth (STD) gravity differences are compared with the AG variations. Using a simple Bouguer plate model, we find that the STD gravity differences are very similar to the AG variations. The STD gravity differences are then used to determine apparent density values. These integrative density values are compared with measured grain densities from core samples to obtain an apparent porosity and saturation change representative of the investigated depth. The apparent porosity ranges from 4.8 to 7.3 per cent. We then discuss on the repartition of the apparent physical properties with respect to the epikarst and infiltration zone karst structures. We argue that AG and STD differences monitor epikarst water storage variations. Within this scope, we discuss the fact that seasonal scale water storage variation occurs predominantly in the epikarst.