Preferential Fluid Flow Pathways In Embankment Dams Imaged By Self Potential Tomography

We invert self-potential data in order to locate anomalous water flow pathways in dams and embankments and to estimate the seepage velocity.

01 Oct 2009
A. Bolève, A. Revil1, F. Janod, J.L. Mattiuzzo, J.-J. Fry

Abstract

The inversion of the self-potential data is performed using the modified singular value decomposition for the inverse problem using a linear formulation of the forward problem. The kernel is solved numerically accounting for the topography of the system and the resistivity distribution, which is independently obtained through electrical resistance tomography. A prior constraint based on finite element modelling of ground water flow can also be used to provide a prior source current density model if needed. This self-potential tomography approach is first with a synthetic case study showing how the position of a preferential fluid flow pathway can be retrieved from self-potential and resistivity data and how the seepage velocity can be obtained inside one order of magnitude. This methodology is then applied to a test site corresponding to a portion of an embankment dam along the Rhône River in France. Two self-potential maps (with 1169 and 2076 measurements, respectively) and four resistivity tomograms are used to locate a leak. One self-potential profile and one resistivity profile are used together to perform the 2D inversion of the self-potential data to locate the anomalous leakage at depth and to estimate the flow rate. The depth at which the preferential fluid flow pathway is located, according to self-potential tomography, agrees with an independent geotechnical test using the Perméafor. This demonstrates the usefulness of  this methodology to detect preferential water channels inside the body of a dam.

 

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