Clinton creek abandoned mine/interim spillway reclamation project—status of the channel restoration effort

Authors: Myers, K; Nahir, M; Gillis, C; Shah, J Download Paper Open access courtesy of:

DOI https://doi.org/10.36487/ACG_repo/2315_037

Cite As:
Myers, K, Nahir, M, Gillis, C & Shah, J 2023, 'Clinton creek abandoned mine/interim spillway reclamation project—status of the channel restoration effort', in B Abbasi, J Parshley, A Fourie & M Tibbett (eds), Mine Closure 2023: Proceedings of the 16th International Conference on Mine Closure, Australian Centre for Geomechanics, Perth, https://doi.org/10.36487/ACG_repo/2315_037



Abstract:
The Clinton Creek Interim Spillway Reclamation Project is located at the site of the former Clinton Creek Asbestos Mine, about 100 kilometres northwest of Dawson City, Yukon Territory, Canada and about 9 kilometres upstream of the confluence of Clinton Creek and the Forty Mile River. The mine was operated from 1968 through 1978 and extracted approximately 12 million Tonnes of serpentine ore from three open pits. Two waste rock dumps were placed along the south side of Clinton Creek. In 1974 the Clinton Creek Waste Rock Dump experienced a mass failure (a lateral spread) resulting in the blockage of the Clinton Creek channel over a reach length of approximately 700 metres, forming a landslide dam and initiating the formation of a new impoundment named Hudgeon Lake. Upon first filling of the new reservoir, the water discharging from Hudgeon Lake began flowing across the surface of the waste rock dam at the interface between the waste rock and the existing colluvial soil and bedrock of the valley slope to the north. The flow began to incise into the soil and waste rock forming the new alignment of Clinton Creek now displaced hundreds of metres to the north and perched some 25 metres above the former Clinton Creek channel and floodplain. The new channel has gradients ranging from about 3% to 6% and averages about 3.6%. This compares to the channel’s original in regime gradient of 0.075%. Erosion of the new channel at the lake outlet prompted concerns about a breach of the landslide dam and efforts to control erosion of the channel using riprap armor and a rock weir, were began in 1981 However, multiple failures during high flow events resulted in damage and the rebuilding of the erosion protection features over the years. In the spring of 2003, an interim spillway structure to arrest the downcutting in Clinton Creek began construction. The design involved a simple trapezoidal channel with a series of drops constructed using rock filled PVC coated galvanized wire gabion baskets. The upper reaches of this spillway structure have held up reasonably well, but the lower reach below what is referred to as Drop Structure No. 4 has experienced multiple severe erosion/headcutting events over time. Subsequent efforts to arrest erosion and stabilize the channel including an articulated concrete block chute structure have also resulted in failure. This paper will describe current, on-going efforts to provide a stable, functioning interim channel that will provide at least a 50-yr facility life and, in the process, address desired improvements in fish habitat and fish migration issues until a final, permanent solution can be funded, designed, and constructed.

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