Hydrogeophysical Data Fusion: Integrating Geophysics and Groundwater Hydrology

Near surface geophysical methods have been widely used in groundwater studies for decades.  Many early (and the majority of current) applications focus on the delineation of hydrogeological units using geophysical techniques.  Over the past decade there has been a greater emphasis on the determination of hydrogeological properties (e.g. permeability) and states (e.g. fluid saturation) through geophysical surveys, although significant challenges exist due, in some cases, to the scarcity of coherent, physically based petrophysical models that relate geophysical and hydrological properties.  These applications have tended to utilize geophysical surveys in a sequential manner: feeding geophysically-derived results into a hydrological model.  However, there is now an increasing awareness of the potential value of embedding geophysical data (rather than the derived model) in a hydrological modelling framework. In this case the geophysical data are inverted in close alignment with the hydrological model(s). Such a methodology offers substantial advantages over the traditional sequential approach as the analysis of geophysical data is ‘informed’ or conditioned by the hydrology but suffers from significant computational overheads and also necessitates a valid hydrological model and suitable petrophysical relationships.  Here, we review the various approaches that allow the incorporation of geophysical data into groundwater hydrology studies and illustrate, through case study, a mechanism for coupling of hydrological and geophysical models. We pay particular attention to what is feasible at present with such approaches and highlight potential future opportunities that will permit greater utilization of geophysical data in studies of groundwater hydrology.