A Case Study of the Self-Potential Method to Characterize Seepage and Earth Dam Materials

This paper presents a case study of the self-potential (S.P.) method applied at the junction of two embankment dams to characterize seepage. Sensitivity of the S.P. method to water runoff can be used to delineate the preferential flow paths. However S.P. can be caused by other sources, therefore only anomalies caused by water flow, described by the electrokinetic (EK) mechanism, are the targets of our study. We take advantage of the controlled progressive emptying and impounding of the upstream reservoir to monitor changes of S.P. due to changes of water flow and the displacement of materials. Also, time-lapse electrical resistivity tomography is used to control the variation of electrical conductivity of the dam material together with changes in water level. It allows for a better discrimination and interpretation of the various self-potential sources. The effective EK coupling coefficient of the dam materials was computed from the variation of potential with water level and flow rate. The S.P. monitoring allowed displaying a positive anomalous zone associated with the reservoir water level changes. It can be related to visible seepage. It is difficult to make a quantitative interpretation of the S.P. data collected at different periods of time using coupled modeling because of the poor knowledge of the hydraulic and physical properties of dam materials.