Assessment of slope stability on logged forest‐hill slopes using ground‐penetrating radar and electrical resistivity tomography

The use of ground‐penetrating radar (GPR) and electrical resistivity tomography (ERT) geophysical methods are considered a useful tool for assessing forest soil slope instabilities. These techniques provide a detailed survey regarding changes because of logging operations in an area, where the combination of soil, water, and rock conditions predisposes to the development of slope instabilities. In the current study, such geophysical survey techniques were applied at two localities, Bukovinka and Zemanův žleb near Křtiny (Southern Moravia, Czech Republic), during three sessions over 1 year. The selected survey sites were on different terrains but the same subsurface (sediments of Lower Marine Carboniferous). The condition for their selection was the absence of other major external influences apart from wood harvesting. The GPR and ERT measurements were carried out along the same lines, and changes in the geophysical profiles over time were observed. The results demonstrate the processes that lead to visible changes on both localities in the results of measurements. Both methods showed shifts in some soil properties configuration, separating partial rock masses or even incipient soil/rock movement. The ERT also detected a significant expansion of wet areas inside both studied rock masses, which may be because of the development of new channels for infiltration of rainwater. Considering that the only major external factor that could change the slopes drainage properties was the wood harvesting, it is reasonable to conclude that the observed changes are associated with the logging operations.