HYDRO-GEOPHYSICAL TECHNIQUES FOR GROUNDWATER CHARACTERIZATION: THE LINK BETWEEN MEASUREMENTS AND MODELING

The characterization of the subsurface from a hydrological point of view requires that the key hydraulic parameters be identified together with the main forcing/boundary conditions. These pieces of information will then contribute towards a correct conceptualization of the system’s components and behavior and ultimately towards the construction of mathematical models capable of reproducing the system’s behavior and predicting its reaction to future changing conditions. Geophysical techniques can provide a key contribution in this direction, provided that they are used to measure changes in the system’s state variables, such as moisture content or tracer concentration, as function of space and time. These data can then be profitably used to calibrate the response of numerical flow and transport models and therefore lead to the identification of the key hydrological parameters. In this talk we will present a few examples of integration of hydrological modeling with time-lapse hydro-geophysical data, using both electrical resistivity tomography (ERT) and ground-penetrating radar (GPR). In particular we will analyze the application of this general methodological framework to the identification of hydrological parameters both in the unsaturated and the saturated zones. In the former, we analyze repeated measurements during natural infiltration processes and man-made irrigation tests, using both surface and borehole measurements. For the latter, we focus our interest on the performing and interpretation of saline tracer tests. In both cases, advantages and disadvantages of the individual approaches will be highlighted. The general message is that the quantitative use of the hydro-geophysical datasets linked to hydrological models requires a proper understanding of the physical methodology, of the constitutive models and of the resolution characteristics of the adopted techniques.