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Landslide Risk Management for the Construction and Operation of the Upper Lillooet River Hydroelectric Facility Near Pemberton, BC

Author: James Haley, Pierre Friele
Conference: Geohazards 7
Date: June 3-6, 2018

ABSTRACT
The Upper Lillooet River Hydroelectric Facility is situated approximately 60 km northwest of Pemberton in southwest British Columbia, Canada. The site is located on the north side of the Mount Meager Volcanic Complex (MMVC), which comprises weak, locally hydrothermally altered rocks and is especially prone to large (>1 Mm3) landslides. Landslide risk management plans were developed for both the construction and operational phases of the project. Under the framework of the landslide risk management plans, the work areas at the site were assigned one of three hazard ratings (Low, Moderate or High). The ratings reflect the return-frequency and magnitude of landside that would be anticipated to affect the work area. A risk analysis was completed taking account of the predicted workforce requirements for each work area and the vulnerability of individuals to the hazards. The landslide hazard from the MMVC is seasonal and conditioned by weather. Four hazard alert levels were defined based on rainfall and temperature criteria. Risk mitigation requirements for each work area were determined with respect to the different hazard alert levels. In moderate and high risk areas, the key mitigation measures implemented at elevated alert levels were the use of a ‘spotter’, restricting access and temporarily implementing ‘Shutdown’ of work. Rainfall and temperature were continually monitored during construction using an on-site climate station, and the mitigation measures were varied accordingly. The landslide risk was exacerbated when, in the summer of 2015, the area was affected by a wildfire. Rock fall and boulder fall hazards were mitigated by undertaking scaling work and constructing a protection berm, and enhanced ‘Shutdown’ procedures were implemented. The management plan for the operational phase of the project incorporates a full Quantitative Risk Assessment for each work area and work activity with respect to Personal Individual Risk. The risk was evaluated against a threshold risk tolerance criteria of 1:10,000 per annum to verify the mitigation requirements.

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