Spatiotemporal imaging of water content and monitoring of seepage hazards in embankments using electrical resistivity tomography method

Reliable detection and monitoring of seepage hazards in embankment dams remain challenging. Conventional approaches, such as drilling, are costly and provide only point-scale information, whereas geophysical methods often rely on indirect proxies that limit intuitive interpretation of seepage processes. To enable efficient and intuitive characterization of seepage hazards, this study proposed a spatiotemporal imaging approach for water content based on high-density electrical resistivity tomography (ERT). In the area of Fangli Reservoir in Yantai City, water content was selected as a direct indicator of seepage hazards. Correlations between water content and geoelectrical parameters of soil and rock-core samples were analyzed to establish a quantitative prediction model. A mixed Lp-norm-constrained inversion method, a 3D geoelectrical reconstruction workflow, and temporal constraints were further introduced to improve the inversion of monitoring data. Two high-density ERT lines were deployed on the downstream slope, and monitoring surveys were conducted during and after the flood season to obtain spatiotemporal images of resistivity and water content. Fiber-optic and hydrogeological monitoring data were used for validation. The imaging results reveal a shallow sandy loam layer with high water content on the downstream slope and delineate its three-dimensional distribution characteristics. Time-lapse imaging indicates that water content increases in some areas during the monitoring period. Displacement, water-level, and water-temperature data suggest no significant structural damage to the embankment. High-water-content anomalies may be associated with insufficient soil compaction, precipitation, and potential seepage. Early warning and strengthened follow-up investigation and monitoring are therefore recommended. The results demonstrate that water-content-based spatiotemporal imaging is effective for seepage hazard detection and monitoring in reservoir embankments.