The links between MRS parameters and the hydrogeological parameters
Résumé
Magnetic resonance sounding (MRS) is a non-invasive geophysical method that can be used to discriminate between the geophysical signals of pore water of the surrounding rock. This method is thus particularly attractive for hydrogeological applications. In order to investigate MRS for the benefit of applied hydrogeology, a comprehensive interdisciplinary study was carried out. The aim of this project was to develop an optimal methodology which could be easily adopted by hydrogeologists. This paper summarizes the main results obtained, with the objective of translating the MRS parameters into parameters that can be directly used by hydrogeologists. It was found that MRS is well adapted to the working scales of the hydrogeologist (i.e. fieldscale, well scale). It is able to provide significant information for the hydrogeologist, including: - Reliable detection of the presence of water in the subsurface. This is the basic and most significant advantage of the method, which proved to be useful, particularly in arid to semi-arid environments. - Locating water-saturated formations (top and bottom), situated at depths between 0 and 100 m approximately. - Estimation of the hydrodynamic parameters of detected aquifers: o Through a rigorous inversion and calibration process, the MRS method enables the quantification of the specific yield (effective porosity) of aquifers and of the storage coefficient, the latter in unconfined aquifers only. o In the present state-of-the-art, MRS is able to estimate the hydraulic conductivity (or transmissivity) of aquifers in localized favourable configurations, when calibration is available; otherwise, aquifers can be compared qualitatively. Thus the MRS method provides data that cannot be obtained with other non-invasive geophysical tools, and is already a valuable tool for applied hydrogeological projects.