Monitoring water flow in the unsaturated zone using georadar

Time-lapse measurements of fluid movements in the subsurface have become increasingly important, not only in the exploration of hydrocarbon reservoirs but also in environmental geophysics. Groundwater contamination from industrial ruins, leaking pipes, rubbish pits without base sealing and the excessive use of fertilizers in agriculture are all reasons for finding a suitable method for detecting fluid flow in the subsoil. To be able to recognize and remove the cause of groundwater contamination it is necessary to trace the path taken by the contamination and to locate its source. Pollutants normally reach the groundwater as drain water. Rainwater seeping into the subsurface does not penetrate as a uniform front but often follows preferential flow paths in the form of so-called ëfingersí (Baker & Hillel 1990; Liu et al. 1994a; Babel et al. 1995).