Application of Self-Potential Method in Detecting Subsurface Fluid Pathways in Owena Dam Catchment, South West Nigeria

Owena Multi-Purpose Dam in Ondo State, South West Nigeria, serves as a critical water supply reservoir for Akure and surrounding communities, yet concerns about seepage through the embankment and foundation have not been addressed through modern geophysical investigation. This study applies the self-potential method to map subsurface fluid pathways and identify zones of preferential seepage within the dam catchment area. A fixed-base measurement configuration was used to acquire self-potential data along 12 profiles across the embankment, abutments, and downstream area, with electrode spacing of 5 metres. Background noise levels were assessed prior to survey using a time series of potential readings at a stable reference station. Anomalies exceeding plus or minus 20 millivolts relative to background are identified as indicative of active fluid flow pathways. Several negative SP anomalies of between -35 and -62 millivolts are located along the left abutment, consistent with downward seepage through a permeable zone in the foundation material. A cluster of positive anomalies in the downstream apron zone suggests upwelling associated with subsurface flow paths bypassing the cutoff trench. These findings are compared with available embankment construction records and piezometric monitoring data. The study provides a non-invasive diagnostic framework for dam safety assessment applicable to other earthen dams in Nigeria. Keywords: self-potential, seepage, dam safety, Owena Dam, fluid pathways