Geophysical Assessment of Internal Erosion Damage in Levees

Abstract This study investigates an internal erosion site along the Crawford County Levee System in Arkansas, USA using electrical resistivity tomography (ERT) lines, complemented by multichannel analysis of surface waves (MASW) and capacitively coupled resistivity (CCR) surveys. The goal of the testing was to identify internal erosion areas and establish “best recommend practices” for future investigations of internal erosion. For the study, CCR surveys successfully characterized the variable foundation deposits, delineated areas with increased susceptibility for internal erosion and areas of existing sand boil occurrences across the site and guided the selection areas for further detailed geophysical investigations. High resistivity anomalies in the ERT data, exhibiting thinning of the conductive top stratum and upward coarse material flow, were interpreted as internal erosion damage zones corresponding to observed sand boils and slope failures. Repeat ERT monitoring captured anomaly changes related to seasonal variations in subsurface conditions. Co-located MASW lines provided shear wave velocity profiles for stratigraphic delineation, with some low-velocity zones correlating to interpreted ERT internal erosion anomalies, though MASW proved less effective than ERT for detailed internal erosion mapping. In an adjacent control area, more favorable geological conditions such as a thicker conductive top stratum contributed to superior performance. The findings demonstrate the ability of ERT to effectively assess internal erosion damage, outperforming MASW, though further testing with comprehensive ground-truthing is recommended to refine interpretations and quantify uncertainties of the study. Overall, geophysical assessments show promise for reliably detecting and characterizing internal erosion damage compared to visual inspections alone.