Current-Injection Transient Electromagnetic Method for Locating the Surface Projection of Seepage-Related Anomalies in Embankment Dams

This study evaluates the current-injection transient electromagnetic method (CITEM) driven by a pulsed current to identify seepage-related anomalies in earth–rock embankment dams. We used a theoretical model of a seepage channel under injected-current excitation to derive complementary localization features from horizontal-response extrema and the spatial gradient of the vertical response. Three-dimensional simulations examined the effects of channel properties and survey geometry. Both features indicated the surface projection of the modeled conductive channel, and higher conductivity generally strengthened the anomalies. Larger channels enhanced the free-decay response, whereas the turn-off response weakened at larger sizes. Increasing observation height reduced anomaly amplitude and spatial gradient, while the free-decay response was less sensitive to electrode position. A field survey at Hongyan Reservoir revealed a continuous anomaly band approximately perpendicular to the dam axis. The processed horizontal-response and vertical-gradient anomalies were spatially consistent, and the band’s downstream end lay near a visible seepage outlet. A representative vertical-gradient profile yielded a spatial anomaly contrast of 54.46. These findings support CITEM for identifying seepage-related anomalies and delineating their surface projections, although the seepage interpretation was not independently confirmed by borehole investigations or tracer tests.