Self potential and temperature monitoring for seepage detection in embankment dams

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Earthen embankment dams are widely used to contain water supplies and hydroelectric reservoirs, as well as wastes such as those produced by mining and oil sands operations. In all cases, there is a need to ensure that any seepage through the dam remains controlled, so as to prevent internal erosion of fine-grained materials and the development of piping, which can lead to collapse and catastrophic flooding or contamination of the environment. UNB and NB Power propose to design, implement and evaluate a novel passive monitoring system for the detection of concentrated water seepage through earthen embankment dams. The project will be based at the Mactaquac Generating Station on the Saint John River near Fredericton, NB, where NB Power would like to monitor the interface between the compacted till core of the embankment dam and the adjoining concrete diversion structure. Although there is no evidence of problematic seepage now, NB Power wishes to enhance its monitoring capabilities in the interest of due diligence, given that the concrete stuctures at Mactaquac suffer from degradation due to Alkali Aggregate Reactivity. Instrumentation will be installed to monitor variations in two parameters influenced by water flow: temperature and electrical self-potentials (SP). Two adjacent boreholes, drilled adjacent to the interface, will be equipped with autonomous fibre optic distributed temperature sensing (DTS) and SP monitoring systems. Additional SP electrodes will be installed on surface on the downstream face of the dam. Design and testing of the SP monitoring system, together with numerical and laboratory modelling of expected temperature and SP responses to various seepage scenarios, will be the focus of a PhD thesis project to be completed over the next 3.5 years. The study site and time frame will allow for improvements to monitoring instrumentation and techniques that are appropriate for large embankment dams operating through cold winters and hot summers.