SALINE PULSE TEST MONITORING WITH THE SELF-POTENTIAL METHOD TO NON-INTRUSIVELY DETERMINE THE VELOCITY OF THE PORE WATER IN LEAKING AREAS OF EARTH DAMS AND EMBANKMENTS

Abstract

A method is proposed to localize preferential fluid flow pathways in earthen embankments with time-lapse self-potential fluctuations associated with a salt tracer injection upstream. This method is first tested using laboratory data then demonstrated at a field site. In the laboratory, a network of non-polarizing electrodes is connected to a highly sensitive voltmeter to record the electrical field fluctuations occurring over time after a salt injection into a sand tank containing a preferential flow channel through a fine sand matrix. The electrical potential distribution is monitored at the surface of the tank to localize the pulse of saline water through the channel over time, and to determine the flow velocity. A finite element model allows us to reproduce the time-lapse electrical potential distribution over the channel, although some discrepancies were observed on the banks. This method applies in real time and can be used to map high permeability flow pathways in earthen embankments that may be spatially localized. We demonstrate the use of this method at a 12 m high, 100 m long earthen embankment by injecting a salt tracer at the crest and monitoring the self-potential and DC resistivity through time on the surface of the downstream slope. Our results clearly display a high permeability preferential flow path that was discovered in the center of embankment during a reconnaissance survey.