Geophysical characterization of the embankment and seepage monitoring at the Chimney Rock Dam near Salina, Oklahoma

This work presents a comprehensive geophysical investigation of the embankment conditions and seepage pathways at the Chimney Rock Dam in Salina, Oklahoma. The study adopts a multi-geophysical framework consisting of three integrated projects designed to tackle pressing dam safety concerns stemming from observed seepage at the toe of the dam. The first project outlined areas of high moisture content and possible seepage pathways using integrated electrical resistivity tomography (ERT), self-potential (SP), and multichannel analysis of surface waves (MASW). The second project consisted of six weeks of time-lapse geoelectrical monitoring during which the reservoir levels varied between 836 and 857 feet in elevation, thereby capturing the spatio-temporal evolution and development of seepage pathways. The results showed the incremental development of resistivity and self-potential anomalies linked to changes in water levels, enabling the mapping of major and minor seepage zones and their preferential flow paths within the dam. The third project aimed to advance the interpretation of the SP results to quantitatively interpret the data. The project developed a new gaussian based Bayesian inversion method providing probabilistic solutions for seepage parameter estimation that overcome the inherent non-uniqueness commonly experienced with the traditional deterministic approaches. Testing and validating with results from literature confirmed the reliability of the method in estimating source parameters, including depth, electric dipole moment, polarization angle, horizontal center of anomaly and related uncertainty quantification. Together, these projects form a sound basis for non-invasive dam integrity assessments, offering important insights for maintenance decision-making and contributing to the wider field of geophysical applications in infrastructure safety assessment. The results of this study provide critical information for characterizing embankment dams, seepage zones and seepage pathways. Such information is critical for mitigating seepage-related hazards and ensuring the long-term safety and functionality of the dam.