Sediment dynamics across gravel-sand transitions: Implications for river stability and floodplain recycling
Bibliographic record
Abstract
Abstract The gravel-sand transition (GST) is commonly observed along rivers. It is characterized by an abrupt reduction in median 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 documented changes in channel stability, suspended sediment concentration, flux, and grain size across the GST of the Karnali River, Nepal. Upstream of the GST, gravel-bed channels are stable over hundred- to thousand-year time scales. 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 GST. The results demonstrate a dramatic change in channel dynamics across the GST, from relatively fixed, steep gravel-bed rivers with infrequent avulsion to lower-gradient, relatively mobile sand-bed channels. The increase in sediment concentration and near-bed suspended grain size may be caused by enhanced channel mobility, which facilitates exchange between bed and bank material. These results bring new constraints on channel stability at mountain fronts and indicate that temporally and spatially limited sediment flux measurements downstream of GSTs 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 distilled prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. Learned from the 10,348 direct Codex labels and 10,348 direct Gemma labels. Candidate is the union of thresholded teacher heads; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels or direct frontier model labels.
Codex and Gemma teacher scores by category
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.000 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.000 | 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 teacher head, 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".