A combination of seismic and electrical resistivity surveys was applied to study a Composite Dam in north-central Nigeria in order to delineate and characterize subsurface features responsible for anomalous water leakage in the dam. Data acquired were processed to image the dam’s subsurface and its surrounding. Subsurface electrical resistivity models of the dam revealed a high-permeable water-saturated section in the form of a conductive zone at horizontal distance of 80– 220 m, from near surface to a depth of about 30 m. The presence of similar structure on resistivity profile lines perpendicular to the dam confirmed the conductive zone and suggested three-dimensionality of the conductive structure. Velocity model computed from seismic refraction data revealed the presence of a low-velocity oxbow structure between 100 and 200 m from near surface to depth of about 20 m. The presence and correspondence of a low-velocity structure with a conductive structure in the dam subsurface, an indication of water-saturated highpermeable rock, was interpreted as the point of water seepage in the dam. The study recommends that the internal geometry of the seepage area should be study in greater details using borehole cores and cuttings in order to design an appropriate anti-seepage rehabilitation intervention.
Note: This paper was accepted into the Technical Program but was not presented at the 2020 SEG Annual Meeting.
