Seepage Diagnosis of Earthen Embankments With Controlled Source Audio Frequency Domain Magnetics (CS-AFD-M)

Wallace, Michael J. (Willowstick Technologies LLC) | Montgomery, Jerry R. (Willowstick Technologies LLC) | Kofoed, Val O. (Willowstick Technologies LLC) | Jessop, Mike L. (Willowstick Technologies LLC)



This paper examines both the theoretical basis and the practical implications of a minimally invasive groundwater mapping method as applied to seepage detection in earthen embankments. The method involves inducing a low voltage, low amperage, low frequency audio electrical current into the groundwater system. This electric current naturally gathers in areas of highest conductivity—which include high porosity regions within the saturated zone. Per the Biot-Savart law—which relates magnetic fields to their source electric currents—the technology can reveal vital information about the location, character and preferential flow paths of the groundwater system through which it is passing. When properly captured, measured, filtered, and reduced, the data derived from that magnetic field can be used to create both twodimensional maps and three-dimensional models of the subsurface electric current distribution some of which can be interpreted as seepage flowpaths. This method can be applied to a host of seepage related issues, especially tracking and pinpointing the leak locations in a dam’s embankment, abutments, foundation or outlet works. This paper will convey the findings of one case study in which the efficacy of this method has been demonstrated on a seepage issue.