Debris Flow Mitigation at the East Gate Landslide

ABSTRACT
This case study presents an alternative approach to debris flow mitigation at the East
Gate Landslide. The site is in Glacier National Park, three and a half hours west of Calgary
along the Trans-Canada Highway. The East Gate Landslide reactivated as a 2,000,000
m3 rock slump in 1997 above the highway and debris flows occur on an annual basis.
Parks Canada, subsequently constructed a large berm structure at the base of the gully
to protect the highway and store volumes.

The debris flows are self-amplifying, with each year resulting in further erosion of the gully
increasing debris flow volumes and costs for removal. Traditional approaches to address
this risk, such as increased hardening of infrastructure to withstand flows or avoidance
through relocation of the highway were determined to have substantial cost impacts.
McElhanney and their partners developed an alternative approach, seeking to address
debris flows at their source with a three-component gully erosion mitigation strategy:

1. Diversions to reduce surface flows.
2. Log crib check dams to reduce flow velocity and limit undermining of side slopes.
3. Revegetation of side slopes through live staking.

This paper focuses on the development, implementation, and performance of mitigation
measures over the past several years, including the construction of six log dams over the
2020 and 2021 construction seasons. Topics include management of site access and
material supply in challenging terrain, dam refinements and lessons learned after multiple
years of debris flows, and next steps towards continued gully stabilization.

Key words: resilience, debris flow, adaptation, log crib check dam, erosion