Monitoring of the soil moisture regime of an earth-filled dam by means of electrical resistance tomography, close range photogrammetry, and thermal imaging

Small earthen dams usually lack a detailed monitoring system that would provide high-resolution data concerning changes in seepage flow. Geophysical methods and remote sensing are useful techniques for non-destructive and non-invasive investigation of subsurface processes. We have utilized a combination of electrical resistivity tomography (ERT), close range photogrammetry, and unmanned aerial vehicle (UAV) thermal imaging techniques to detect specific superficial and internal structures of a historical earth-filled dam. Longitudinal and transversal profiles of a typical fishpond dam in the Czech Republic were measured. The dam was constructed during the fifteenth century, but has since gone through some minor reconstruction. The aims of the applied geophysical methods are to detect and localize the boundary of the dam foundation, new earth material from reconstruction, the cone of water depression, the reservoir’s outlet location, potential internal erosion, cavities, and heterogeneity in water content pattern and any other anomalies. The primary results show that ERT is suitable to detect dam stratification and large anomalies. The UAV monitoring system provided reliable data for a surface temperature distribution map which corresponded well to topsoil water content and electrical resistivity.