Usefulness of Magnetic Resonance Soundings to Constrain Groundwater Modelling

The unconfined aquifer in southwest Niger was intensively studied over the last decades. However, the transient numerical modelling that was conducted over the area suggested that additional field storativity and hydraulic conductivity measurements are needed. To check the capability of magnetic resonance sounding (MRS) to improve the knowledge of this aquifer, a survey was conducted in Niger in December 2005. We found that (1) the depth to the water table is estimated by MRS with an acceptable accuracy to survey poorly documented areas. (2) After a parameterization process, the transmissivity is accurately estimated from MRS. (3) MRS water content is linked to the total porosity calculated with the Bretjinski formula. However, MRS water content still needs to be parameterized with new measurements to quantify the specific yield and the total porosity. We finally found that MRS is useful to better constrain groundwater modelling of such large unconfined aquifer. (1) MRS depth to the water table can be used as head boundary in the numerical model (2) The range of realistic transmissivity and storativity values that could be used in the model can be estimated from MRS.