Simultaneous Solving of Three-Dimensional Gravity Anomalies Caused by Pumping Tests in Unconfined Aquifers

The contribution of geophysical techniques to groundwater characterization has largely evolved during the last two decades. As gravity is a geophysical technique sensitive to underground mass variations and due to the improved resolution of modern gravity meters, it can provide information on changes in the phreatic level caused by water being pumped from unconfined aquifers. Previous studies simulated the hydraulic head and the gravimetric anomaly using independent codes. The mass change associated to the pumping well-simulated drawdown had to be externally transferred to the gravity code used to simulate the gravimetrical anomaly, which has severe drawbacks. This article describes how to solve the forward coupled hydro-gravity problem using a unique finite-element code. To illustrate it, it is shown the case of a two-dimensional hydraulic model coupled to its three-dimensional gravity anomaly and also a more complex case where both related domains are three-dimensional. Both are compared against analytical solutions and discussed. The methodology is very flexible, general and amenable to extensions like including heterogeneous domains or coupling with the inverse problem in the same loop.