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Closure spillway for the plantsite tailings dam, Quintette Operating Corporation Sharman, Kevin
The Quintette mine was a large open pit coal mine in Northeastern BC which produced 65 million tonnes of high quality metallurgical coal from 1983 until its closure in 2000. The tailings dam at the mine is up to 50 meters high, and retains approximately 11 million cubic meters of tailings. A spillway was required to allow storm water management at closure. Further, for long term dam stability, it was desirable to minimize the amount of ponded water. Numerous design options were examined, including a notch in the dam crest with a rip rap-lined channel on the downstream face. Since this was to be a closure spillway, long term, no maintenance performance was essential. The design option chosen was a wide, low gradient geomorphic spillway, sized to pass the 1000 year return period rain event. As the design flow velocities are low due to the low gradient, no rip rap was required in the design. Construction of the spillway meant excavating tailings so that the spillway floor would be either in native till or competent fill. This was accomplished by dumping a causeway of rock along the spillway alignment which squeezed tailings ahead of it. The channel was then cut to grade, and a low flow meandering channel was built to carry normal flows. Revegetation of the channel side slopes was enhanced with erosion control mats and the addition of annual barley to the standard seed mix for coarse refuse and tailings. Willow cuttings were planted in a wide swath around the spillway inlet. The net result was a practical, long term solution for a closure spillway.
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