CLIENT:Rio Tinto/Iron Ore Company of Canada (IOC)

LOCATION: Quebec and Labrador, Canada

The Trans-Canada Highway (TCH) is the main east-west connection between Calgary, AB, and Vancouver, BC. In 1997, the East Gate Landslide reactivated as a 2,000,000 m3 rock slump highway. The landslide traveled only about 1000 m and did not reach the TCH. Since 1999, debris flows originating in the landslide deposit and the gully network below it reach the TCH at least once per year.

BGC carried out a detailed geomorphological assessment and found that the gully system continues to incise, causing a self-amplifying cycle of downcutting and side-slope landslides. About three quarters of the sediment is mobilized within the main gully located downstream of the East Gate Landslide. Previously constructed basins (80,000 m3 storage capacity) retain debris and protect the highway. The already burdensome sediment removal efforts and cost are anticipated to increase and exceed storage capacity as the source area increases.

Instead of continuing to treat the hazard at the highway, BGC developed a gully erosion mitigation strategy to reduce the sediment volumes at the source. This included:

  • Diversions to reduce surface flows in main gully
  • Log crib check dams to control gully grade and limit undermining of gully side slopes
  • Revegetation of side slopes improving slope stability and reducing surface erosion

While the gully erosion mitigation is being implemented, a phased, observational approach in adaptive hazard management is applied. A pilot built in 2020 includes a 6 m tall log crib check dam and initial revegetation plots. The pilot provides valuable insights to improve design and cost effectiveness that can be scaled for the mitigation of the entire project. BGC continues to support the prime civil consultant McElhanney as the mitigation works are being implemented.