Fluvial erosion of glacial tills in Ontario: erosion mechanics, critical shear stress and geotechnical properties
Bibliographic record
Abstract
Quaternary glacial deposits have covered much of southern Ontario in till. Rivers incised into this cohesive sediment have been little studied. Land use change and climate change are increasing river flows leading to increased erosion. To determine the range of erosional resistance of tills, as well as the effects of weathering due to freeze-thaw cycles and wet-dry cycles, the erosion mechanisms and critical shear stress of glacial tills from two Ontario rivers, the Otonabee River in Peterborough, and Medway Creek in London, were studied. Till samples were collected at one in-stream location along the Otonabee River and at two locations on Medway Creek – from the riverbank of a tributary and from eroded pieces collected from a main-stream pool. Geotechnical tests were performed on the samples at the Geotechnical Laboratory of l’Université de Sherbrooke. The samples, once prepared for testing under submerged moisture content, fully dried, or after a freeze-thaw cycle, were tested in a straight hydraulic flume at McGill University. Critical shear stresses of the tills at approximately in-situ moisture content (submerged) at Medway Creek’s two locations were 8.2-8.7Pa. The main mechanism of erosion was mass erosion occurring near natural planes of weakness such as cracks or near gravel particles. The mass erosion rates at critical shear stress were 10.5-10.6 g/hr, while increased erosion rates were observed at above-critical shear stresses, and decreased erosion rates at below-critical shear stresses (never zero). The results at the Otonabee River site were inconclusive due to an undefined drying of the sample before collection at the river site. Preparation and testing of the samples demonstrated that sample preparation by cylindrical coring is superior to cutting the sample to size with a band saw, likely due to sample disturbance. The effect of drying on the samples was a large decrease in erosional resistance, with critical shear stress values of 0.15-0.16 Pa at the Medway Creek and mass erosion rates of 112.2 - 179 g/hr. The dried samples lost cohesiveness and integrity leading to upheaval upon wetting and rapid mass erosion of small particles. Samples subjected to one freeze-thaw cycle also had decreased erosional resistance, with critical shear stress values of 1.14 - 1.5 Pa. The mechanisms of erosion here resembled those of the submerged experiments, with mass and flake erosion around planes of weakness being the main mechanism
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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 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.001 | 0.001 |
| Science and technology studies | 0.002 | 0.001 |
| Scholarly communication | 0.001 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.002 | 0.000 |
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".