Using geophysical data to assess groundwater levels and the accuracy of a regional numerical flow model

The use of geophysical data to accurately determine water levels is demonstrated for an aquifer within the Saint-Narcisse moraine in the Mauricie region of southeastern Québec, Canada. Two numerical simulations were conducted using FEFLOW, one based on regional piezometric data and the other using geophysical data; the data were acquired through transient electromagnetic (TEM), electrical resistivity (ERT), and ground-penetrating radar (GPR) surveys. The three-dimensional geological and groundwater flow model was based on data from 94 boreholes, 5 stratigraphic cross-sections, and 20 TEM, 6 ERT (~1.44 km) and 4 GPR (~0.97 km) surveys. Both numerical analyses confirmed the simulated water levels, and the root mean square errors obtained from the piezometric data and the multiple geophysical techniques were similar at 3.81 and 2.76 m, respectively. Through a discrete modeling approach, this study shows that groundwater levels estimated using geophysical tools and methods and those determined by direct observation are comparable. The outcome illustrates how geophysical data can complement direct observations to provide additional hydraulic information to hydrologic modellers. Geophysical surveys provide an extensive set of soft data that can be leveraged to improve groundwater flow models and determine groundwater levels, particularly in areas characterized by limited direct piezometric information.