Systems-level geohazard risk assessment in southwestern British Columbia, Canada

In Western Canada, geohazards can be related to tectonic events, such as earthquakes and volcanoes, but many are weather-driven events, such as floods, landslides, rockfalls, and snow avalanches. Anthropogenic activities, such as residential development, infrastructure, and climate change also contribute to and increase the overall risk from, geohazards. A recent example is the atmospheric river event that devastated much of the southern British Columbia (BC) province in November 2021. Between November 14 and 15, 2021, a 2,500 km long plume of moisture (atmospheric river) hit the west coast of BC and accumulated significant rainfall breaking 20 rainfall records across the province. This intense rainfall event resulted in regional flooding and triggered numerous landslides across the southern province. The impact included closures of all major transportation corridors, severed rail lines, with no rail connections between Kamloops and Vancouver, and evacuation of close to 15,000 residents.In Western Canada, many geohazards risk assessments are performed within the risk management framework outlined by the Canadian Standards Association. Though guidelines exist, such as the Canadian Technical Guidelines on Landslides, there is no national or provincial standard for managing risk associated with geohazards. Furthermore, BC’s Municipalities Act, which allows individual municipality jurisdictions to manage their own risk, results in uneven distribution of funding and almost always results in emergency response. The insured losses from the November 2021 atmospheric river event are estimated to be $500 million CAD ($370 million USD) and uninsured losses are $9 billion CAD ($6.7 billion USD) and counting. These losses do not account for economic losses due to the closure of major transportation infrastructure networks.Immediate efforts following the November 2021 atmospheric river event focused on opening the major highway routes. However, the rebuilding of failed bridge and highway embankments is considered a temporary solution and further upgrades in designs are needed to account for the increasing frequency and magnitude of future atmospheric river events. With limited resources at all levels of government, the risk associated with regional-level geohazard triggers needs to be better understood in order to prioritize road infrastructure capacity. Keeping the critical highway arteries open is important not only for economic benefits but to allow for emergency access for communities.This research looks to help prioritize road infrastructure capacity based on its vulnerability to atmospheric river-triggered geohazard events. Information related to road closures, geohazard events, and infrastructure damages is compiled and related to preconditions of weather trends and infrastructure capacity leading up to the November 2021 event. Road network analysis is performed by defining consequence assessment parameters, such as average daily traffic, associated economic revenue, availability of safety stopping zones, and infrastructure redundancy. Then the risk is assessed based on the vulnerability assignment of different segments of the road network which is presented in a criticality map.

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