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Towards Quantitative, Spatially Resolved Estimates of Dam Seepage by Time-Lapse Electrical Resistivity Imaging (ERI)
- Publisher: European Association of Geoscientists & Engineers
- Source: Conference Proceedings, NSG2023 3rd Conference on Geophysics for Infrastructure Planning, Monitoring and BIM, Sep 2023, Volume 2023, p.1 - 5
Abstract
Summary
The Mactaquac hydroelectric generating station, located near Fredericton, New Brunswick, Canada has served as a test site for the development of geophysical dam condition monitoring techniques, for close to a decade. Efforts have focused on the region spanning the interface between the clay-till core of the dam and the wall of the adjacent concrete diversion sluice-way. Distributed temperature sensing (DTS) in a borehole drilled into the concrete suggests preferential seepage is present at relatively shallow depth. Since 2019 we have implemented time-lapse electrical resistivity imaging (ERI) – seeking to use seasonal changes in resistivity of the reservoir water as a tracer for imaging regions of preferential seepage through the core. Between April and December 2022, the resistivity of water in the reservoir varied by nearly a factor of four, being most resistive (∼300 Ohm-m) in the spring following snow melt, and most conductive (∼75 Ohm-m) in mid-August due to both elevated temperature and total dissolved solids (TDS). Order-of-magnitude estimates for seepage flux are found from the time lag between resistivity changes measured in the reservoir and correlated changes imaged in the core. Seepage estimates within the upper core are significantly higher than expected, corroborating prior inferences from the DTS system.
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