Characterization of water movement in a reconstructed slope in Keokuk, Iowa, using advanced geophysical techniques

This project addresses the topic of evaluating water movement inside a hillslope using a combination of conventional and advanced geophysical techniques. While slope dynamics have been widely studied, ground water movement in hills is still poorly understood. A combination of piezometers, ground-penetrating radar (GPR), and electrical resistivity (ER) surveys were used in an effort to monitor fluctuations in the subsurface water level in a reengineered slope near Keokuk, Iowa. This information, integrated with rainfall data, formed a picture of rainfall-groundwater response dynamics. There were two hypotheses: 1) that the depth and fluctuation of the water table could be accurately sensed using a combination of monitoring wells, ground-penetrating radar and resistivity surveys; and 2) that the integration of data from the instrumentation array and the geophysical surveys would enable the characterization of water movement in the slope in response to rainfall events. This project also sought to evaluate the utility and limitations of using these techniques in landslide and hydrology studies, advance our understanding of hillslope hydrology, and improve our capacity to better determine when slope failure may occur. Results from monitoring wells, stratigraphy, and resistivity surveys at the study site indicated the presence of a buried swale, channelizing subsurface storm flow and creating variations in groundwater. Although there was some success in defining hydrologic characteristics and response of the slope using this integrated approach, it was determined that GPR was ultimately not well suited to this site. However, the use of GPR as part of an integrated approach to study hillslope hydrology still appears to hold potential, and future work to further evaluate the applicability and potential of this approach would be warranted.