Field comparison of selected methods for vertical soil water content profiling

High-resolution information about vertical variations in soil water content is important for applications ranging from agricultural water management to flow and transport modeling. Commonly applied tools for the investigation of vertical soil water content distribution in hydrogeological field investigations are: gravimetric laboratory analyses of soil samples, logging a cased borehole using a tool with a radioactive source (neutron probe), or yet less well established, direct push-based moisture sensor probes. Due to differences in their underlying measurement principles as well as different operation modes, each of the aforementioned methods is associated with certain advantages and limitations. A common field evaluation of these methods has not been performed until now – raising the question of how well these individual methods perform when applied under different depositional and hydrogeological conditions. For field evaluation direct push-profiling was performed at three different test sites under different hydrogeological settings and varying degree of sediment heterogeneity and compared with results obtained from gravimetric analysis of soil cores and neutron probe measurements. In direct comparison the applied direct push-based Water Content Profiler proved to be a suitable alternative to neutron probe technology for measuring the vertical water content distribution. Moreover, the Water Content Profiler proved to be advantageous over gravimetric analysis in terms vertical resolution and time efficiency. Results of this study identify application-specific limitations of the methods and thereby highlight the need for careful data evaluation, even though some of the methods described in this paper are well established.