Geophysical and hydrological data assimilation to monitor water content dynamics in the rocky unsaturated zone

Abstract

In recent years, geophysics is increasingly used to study the flow and transport processes in the vadose zone. Particularly, when the vadose zone is made up of rocks, it is difficult to install sensors in the subsurface to measure hydrological state variables directly. In these cases, the electrical resistivity tomography (ERT) represents a useful tool to monitor the hydrodynamics of the infiltration and to estimate hydraulic parameters and state variables, such as hydraulic conductivity and water content. We propose an integrated approach aimed at predicting water content dynamics in calcarenite, a sedimentary carbonatic porous rock. The uncoupled hydrogeophysical approach proposed consists in 4D ERT monitoring conducted during an infiltrometer test under falling head conditions. Capacitance probes were installed to measure water content at different depths to validate the estimations derived from ERT. A numerical procedure, based on a data assimilation technique, was accomplished by combining the model (i.e., Richards' equation) with the observations in order to provide reliable water content estimations. We have used a new data assimilation method that is easy to implement, based on the ensemble Kalman filter coupled with Brownian bridges. This approach is particularly suitable for strongly non-linear models, such as Richards' equation, in order to take into account both the model uncertainty and the observation errors. The proposed data assimilation approach was tested for the first time on field data. A reasonable agreement was found between observations and predictions confirming the ability of the integrated approach to predict water content dynamics in the rocky subsoil.

Monitoring the Drainage Efficiency of Infiltration Trenches in Fractured and Karstified Limestone via Time-Lapse Hydrogeophysical Approach

“…An approach based on the inversion of the resistance ratios measured at different time points with respect to the background was adopted to enhance time-lapse resistivity changes [19]. This approach was widely used to track small variations in resistivity over time [48][49][50][51][52]. It is particularly suited to electrically noisy sites because the modeling errors and data errors correlated over different time steps are minimized, and imaging artifacts that typically would occur in a standard inversion are avoided.…”

Evidence of Preferential Flow Activation in the Vadose Zone via Geophysical Monitoring

“…According to the procedure adopted in [30], a formulation of Archie's law [31] was used to convert the inverted resistivity ratios directly into saturation degree…”

Analysis of the Infiltration Complex System Using a Novel GSA-Hybrid for Automatic Calibration Focused at Civil Construction

“…As aforementioned, these parameters values are hampered to obtain in the field due to being in subsurface regions as compared to the facility to collect superficial zone data. In order to assist in solving Richards equation heuristic mathematical models were adopted such as the constitutive models and the inverse model [11][12].…”