Sediment dynamics across gravel-sand transitions: Implications for river stability and floodplain recycling
Bibliographic record
Abstract
The gravel-sand transition is observed along most rivers. It is characterized by an abrupt reduction in median bed grain size, from gravel- to sand-size sediment, and by a shift in sand transport mode from wash load-dominated to suspended bed material load. We document changes in channel stability, suspended sediment concentrations, flux and grain size across the gravel-sand transition of the Karnali River, Nepal. Upstream of the gravel-sand transition, gravel-bed channels are stable over hundred to thousand-year timescales. Downstream, floodplain sediment is reworked by lateral bank erosion, particularly during monsoon discharges. Suspended sediment concentration, grain size and flux reveal counterintuitive increases downstream of the gravel-sand transition. The results demonstrate a dramatic change in channel dynamics across the transition, from relatively fixed, steep gravel-bed rivers with infrequent avulsion to lower gradient, relatively mobile sand-bed channels. The increase in sediment concentrations and near-bed suspended grain size may be caused by enhanced channel mobility, which facilitates exchange between bed and bank materials. These results bring new constraints on channel stability at mountain fronts, and indicate that temporally and spatially limited sediment flux measurements downstream of gravel-sand transitions are more indicative of flow stage and floodplain recycling than of continental-scale sediment flux and denudation rate estimates.
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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 | 0.000 | 0.001 |
| Scholarly communication | 0.001 | 0.001 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 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".