hydrogeophysical

Hydrogeophysics is an interdisciplinary field combining hydrogeology and geophysics to characterize groundwater systems and vadose zone processes. It uses noninvasive and minimally invasive geophysical measurements to infer subsurface properties that govern groundwater flow, storage, and transport, such as hydraulic conductivity, porosity, water content, salinity, temperature, and aquifer geometry.

Common methods include electrical resistivity tomography (ERT) and induced polarization, magnetotellurics (MT), seismic refraction and reflection, surface wave methods, ground-penetrating radar (GPR), and electromagnetic methods. Borehole geophysics and nuclear magnetic resonance (NMR) provide in-situ logs of pore water content and other properties. Time-lapse (4D) hydrogeophysics tracks changes over time due to pumping, recharge, or contamination. Thermal methods and SP potential measurements are also used.

Applications include groundwater exploration, mapping plume migration, delineating aquifer boundaries, assessing recharge and flow paths, monitoring saline intrusion, waste disposal sites, and karst and fractured rock systems. Integrated hydrogeophysical programs often combine geophysical data with hydrological measurements and numerical models to estimate hydraulic conductivity, porosity, and contours of water saturation.

Challenges include non-uniqueness of interpretations, scale differences between geophysics and hydrology, uncertain petrophysical relationships, and the need for calibration with borehole data and hydrological observations. Advances in joint inversion, Bayesian assimilation, and machine learning are expanding the reliability and resolution of hydrogeophysical inferences.