Ecohazard posed by a rockslide that blocked salmon migration in the Fraser River, British Columbia
Bibliographic record
Abstract
On November 1st, 2018 the Big Bar Landslide temporarily blocked Fraser River, the most productive salmon-bearing watershed in Canada, presenting a barrier to upstream salmon migration in 2019 and 2020. The landslide is an example of an ecohazard, similar to a natural hazard, but with immediate and direct impacts on the biosphere, rather than on people and infrastructure. Like natural hazards, ecohazards have cascading effects, where a geophysical process triggers additional events, often with dramatic consequences. The Big Bar Landslide originated from collapse of a steep bedrock wall and deposited 89,000 m3 of rock into one of the narrowest sections of the Fraser River, damming the channel for over 7 hours, and impounding 650,000 m3 of water. The rockfall debris formed a bank to bank step with an ‘overfall’ that was ~4 m at low flow and ~7 m at high flow. The overfall resembled a waterfall, but without a freefall into a plunge pool. A backwater formed upstream that extends ~750 m upstream at low flow, but several kilometers at high flow trapping incoming sediment. The overfall generated a hydraulic barrier to upstream salmon passage, and significantly impeded salmon migration to the Upper Fraser Basin in 2019 and 2020, but rock work has partially ameliorated the impact. Fish passage monitoring indicates success in passing the landslide in 2019 was species and discharge dependent with population-specific estimates ranging from <1% to over 80% success. Passage success was particularly low for early timed populations exposed to the highest flow in 2019; so few fish successfully migrated to the spawning grounds that there was a risk of functional extinction of those runs. There is an ongoing risk to all salmon populations above the landslide until hydraulic conditions at the slide stabilize. The event will have cascading effects on upstream ecosystems, Indigenous peoples who rely on the salmon fishery throughout the Fraser River Basin, and commercial ocean fisheries, but the extent of the cascading effects is not yet known. Collapse of bedrock canyon walls, like the one that started the ecohazard cascade in the Fraser River, are geologically commonplace, but the risk they pose to migratory fish populations in mountainous river systems is largely unknown.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.010 | 0.002 |
| Scholarly communication | 0.002 | 0.000 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.001 | 0.002 |
| Insufficient payload (model declined to judge) | 0.010 | 0.001 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".