The summer of 2021 witnessed an unprecedented flooding event along the Yukon River. Record high water levels and flows caused damage to the boat lock at the Lewes River control structure, located approximately 40km southeast of the City of Whitehorse.
YEC decided to utilize the boat lock as an additional flow conveyance channel to help mitigate the flooding upstream in Marsh Lake. The gates of the boat lock were welded open to ensure that they were not operated during the flood event. The gates were vandalized and closed and ended up damaged from the high flows and water levels. They were taken out of the boat lock and permanently removed from service.
While the flood waters had receded, there was additional damage to the boat lock structure itself. Upon closing a majority of the control structure gates for winter operations, it had increased the flow velocity through the boat lock. Erosion had been identified on the downstream shoreline, just north of the end of the boat lock. Within a couple of days, a large area of erosion occurred, which led to the damaging of the sheet pile and tie backs. A rip rap coffer dam was installed upstream of the boat lock, along with a sluice gate within the boat lock, to mitigate the flows. The downstream erosion areas were protected by rip rap.
There were two additional areas of erosion that occurred. One was within the sheet pile island. The void at the downstream end was identified two days after the initial erosion occurred. The other was a void that occurred at the upstream, shoreline side.
The following figure shows the areas of erosion that occurred during the fall of 2021. The areas identify the propagation of the erosion, and the dates that they were recorded.
