%0 Journal Article
%9 ACL : Articles dans des revues avec comité de lecture répertoriées par l'AERES
%A Legchenko, Anatoli
%A Descloitres, Marc
%A Bost, Adelphe
%A Ruiz, Laurent
%A Reddy, M.
%A Girard, J.F.
%A Sekhar, M.
%A Kumar, M.S.M.
%A Braun, Jean-Jacques
%T Resolution of MRS applied to the characterization of hard-rock aquifers
%D 2006
%L PAR00001022
%G ENG
%J Ground Water
%@ 0017-467X
%M CC:0002386553-0012
%N 4
%P 547-554
%U https://www.documentation.ird.fr/hor/PAR00001022
%> https://www.documentation.ird.fr/intranet/publi/2006/08/010035703.pdf
%V 44
%W Horizon (IRD)
%X The performance of the Magnetic Resonance Sounding (MRS) method applied to the investigation of heterogeneous hard-rock aquifers was studied. It was shown using both numerical modeling and field measurements that MRS could be applied to the investigation of the weathered part of hard-rock aquifers when the product of the free water content multiplied by the thickness of the aquifer is >0.2 (for example, 10-m-thick layer with a 2% water content). Using a currently available one-dimensional MRS system, the method allows the characterization of two-dimensional subsurface structures with acceptable accuracy when the size of the subsurface anomaly is equal to or greater than the MRS loop. However, the fractured part of hard-rock aquifers characterized by low effective porosity (<0.5%) cannot be resolved using currently available MRS equipment. It was found that shallow water in the weathered part of the aquifer may screen MRS signals from deeper water-saturated layers, thus further reducing the possibility of investigating deeper fractured aquifers. A field study using the NUMISplus MRS system developed by IRIS Instruments was carried out on an experimental watershed in southern India. A heterogeneous unconfined aquifer in a gneissic formation was successfully localized, and MRS results were confirmed by drilling shortly after the geophysical study. The top of the aquifer revealed by MRS was found to be in a good agreement with observed static water level measurements in boreholes.
%$ 066