Big Bar Landslide

On November 1, 2018, the Big Bar Landslide partly blocked the Fraser River, creating a hydraulic barrier to salmon passage at moderate to high flows and significantly impeding salmon migration to the Upper Fraser Basin. The Big Bar Landslide jeopardizes salmon populations in the Upper Fraser Basin until the slide material is either removed or fish passage is accommodated by an engineered solution, but this landslide is not unique – the chance of future slides in the Fraser Canyon is real, and past landslides have likely shaped current salmon biodiversity.

Past: Impact of Historical Landslide Events on Salmon

Events similar to the Big Bar Landslide are common in the bedrock canyons of the Fraser River and can have devastating impacts on Fraser River salmon. In 1914, the Hell’s Gate Landslide blocked upstream salmon migration and ~1000 years ago, the Texas Creek Landslide entirely dammed the Fraser River. Though periodic landslides are key selection events in the history of salmon and likely shaped the life histories and genetics we see today, landslides are poorly documented and their frequency and magnitude along the Fraser River is unknown. We will examine the impacts of past landslides in the Fraser Canyon using Light Detection and Ranging (LiDAR) data and surface exposure dating to establish a chronology of river blockages that can be compared to proxies of salmon abundance.

Present: Impact of the 2018 Landslide

The Big Bar Landslide is not unique and hydraulic barriers to upstream salmon migration exist at many places in the Fraser River (e.g., Black Canyon, Hell’s Gate) and cause significant mortality. However, what flow conditions impede upstream salmon migration in turbulent rivers are not well known and the Big Bar Landslide is an opportunity to examine how flow dynamics in the Fraser River affect fish passage and diversity. We will identify existing hydraulic barriers and the river morphologies that produce them, explore the biological characteristics and behaviors that salmon use to navigate these barriers, and investigate how barriers such as the Big Bar Landslide shape the genetic diversity of salmon.

Future: Assessment of Potential Future Landslide Events

Within the bedrock canyons of the Fraser River, there are over 100 sites with the same morphology as the Big Bar Landslide site: a narrow section of the river with a deep downstream pool where the bedrock walls of the canyon are undercut. Undercut canyon walls are more susceptible to failure and suggests other river blocking landslides could occur in the future and devastate Fraser salmon populations. We will identify where river morphologies linked to landslides occur and the geomorphic and biologic consequences of potential future landslide events.

Anticipated Benefits

Natural hazards, such as the Big Bar Landslide, can create crises for salmon and their management. There is an urgent need for integrative and collaborative science on landslides and salmon to advance management responses and proactive risk mitigation. Mapping and dating past landslides provides information on the frequency and magnitude of river blocking landslides in the Fraser River. Identifying potential sites of future landslides provides critical information necessary for geotechnical engineers to assess landslide risk, planning for future landslides and mitigation efforts.  Knowing how the Big Bar Landslide impacted river morphology and flow, fish migration, and Fraser salmon genetics and risk mapping will help predict which populations are at risk of new river blockages and inform restoration efforts to maintain sustainably managed fish stocks. Further, the proposed work will inform implementation and upgrading of critical infrastructure through river engineering interventions to enable successful fish migration.

Anticipated Outcomes

Our project will produce a better understanding of how catastrophic changes in river channel morphology (e.g., landslides, rockslides, etc.) have affected Fraser salmon in the past, how the Big Bar Landslide is presently affecting Fraser salmon, and how and where future landslides will likely affect Fraser salmon.  We will produce and share i) maps of potential future landslides and probable hydraulic barriers to fish passage for the entire Fraser Canyon, ii) spatially-resolved information of environmental (topography and velocity) and biological controls (fish body size, species) on upstream fish migration, iii) evaluations of how the Big Bar Landslide affected fish genetics, and iv) information on the historic frequency and magnitude of river blockages in the Fraser Canyon and how this could have shaped present-day salmon biodiversity.

Community and First Nations Engagement

We are working with Fraser Basin Council and the Fraser Salmon Management Council to engage in community outreach and information sharing.