The emergence of hydrogeophysics for improved understanding of subsurface processes over multiple scales

Abstract

Geophysics provides a multidimensional suite of investigative methods that are transforming our ability to see into the very fabric of the subsurface environment, and monitor the dynamics of its fluids and the biogeochemical reactions that occur within it. Here we document how geophysical methods have emerged as valuable tools for investigating shallow subsurface processes over the past two decades and offer a vision for future developments relevant to hydrology and also ecosystem science. The field of “hydrogeophysics” arose in the late 1990s, prompted, in part, by the wealth of studies on stochastic subsurface hydrology that argued for better field‐based investigative techniques. These new hydrogeophysical approaches benefited from the emergence of practical and robust data inversion techniques, in many cases with a view to quantify shallow subsurface heterogeneity and the associated dynamics of subsurface fluids. Furthermore, the need for quantitative characterization stimulated a wealth of new investigations into petrophysical relationships that link hydrologically relevant properties to measurable geophysical parameters. Development of time‐lapse approaches provided a new suite of tools for hydrological investigation, enhanced further with the realization that some geophysical properties may be sensitive to biogeochemical transformations in the subsurface environment, thus opening up the new field of “biogeophysics.” Early hydrogeophysical studies often concentrated on relatively small “plot‐scale” experiments. More recently, however, the translation to larger‐scale characterization has been the focus of a number of studies. Geophysical technologies continue to develop, driven, in part, by the increasing need to understand and quantify key processes controlling sustainable water resources and ecosystem services.

Scaling, similarity, and the fourth paradigm for hydrology

“…Advances in citizen science (Buytaert et al, 2014;Hut et al, 2016) and the use of so-called "soft" data for hydrological modeling (Van Emmerik et al, 2015;Seibert and McDonnell, 2002) show that even though these new data are collected on nontraditional spatiotemporal scales, they might give us new insights into how processes on different scales are coupled. Advances in hydrogeophysical characterization of the subsurface (Binley et al, 2015), such as electrical methods, ground-penetrating radar, and gravimetry, offer non-invasive mesoscale information that can be used to provide parameters or to infer boundary conditions, states, or fluxes. Recently, Christensen et al (2017) demonstrated that dense airborne electromagnetic data can be used to map hydrostratigraphic zones, which is an encouraging capability.…”

Geophysical and Hydrogeological Groundwater Prospectivity Mapping in the Kraaipan Granite-Greenstone Terrain, Southeast Botswana

“…Determination of petrophysical relationships used to link the geophysical properties to hydrological properties is also considered [4] [6] [10]. Eventually, the studies seek to quantify subsurface architecture that influence flow (such as hydrostratigraphy and preferential pathways); and estimate hydrological properties (such as porosity) and state variables (such as saturation) ( [15] [16] and references therein).…”

Challenges in monitoring and managing engineered slopes in a changing climate

“…Electrical Resistivity Tomography (ERT) is a ground imaging technique that is being increasingly applied to the characterisation and monitoring of the subsurface [17]. Resistivity is particularly sensitive to changes in pore fluid resistivity and saturation as the principal mode of current flow in the subsurface is through electrolytic conduction in the pore fluid; consequently, ERT is widely used in hydro-geophysical investigations [18].…”