Small-scale changes in bed morphology and sediment transport under waves and currents
Bibliographic record
Abstract
Understanding the behaviour of bedforms and the related sediment transport is a key issue in coastal science and engineering. The generation of bedforms and the transport of sediment are part of a highly complex interactive system, involving feedback between a turbulent flow and the bed morphology. The present study applies an integrated approach to the 'trinity' of: boundary layer structure; sediment transport; and bedform development (Best, 1993). In addition to the interactions between the bed and flow, the investigation contributes to the understanding of the combined-flow influence on sediment transport and bedform dimensions. The data considered in this study fall into two categories: strong currents, with no or low wave activity (INDIA, Day 51 and 58, respectively); and weak currents in the presence of large waves (Ralph). The INDIA data release to a tidal inlet channel (Ria Formosa, Portugal) and the Ralph data to an offshore coastal shelf site (Nova Scotia, Canada). Sediment transport and bedform geometry respond to the maximum conditions over a wave orbit, with the influence of waves being detectable even when the mean enhancement of shear stress is low. The ratio of Hs/d influences the effectiveness of the wave-current ratio, in determining the dominant hydrodynamic regime on the bed. Shear stress is enhanced by both waves and bedforms, simultaneously, in a non-linear manner. The migration of bedforms also acts to increase shear stress, indicating that both shape and movement of bedforms affects boundary layer flow. Macro-turbulent structures were observed, with a strong local effect on the shear stress. These features relate to and migrate with the bedforms. This result has significant implications in terms of modelling flow over bedforms i.e. the use of a spatially-averaged shear stress (or roughness) may not be sufficient to account for this behaviour. On Day 51, the drag coefficient was of the order 0.0032. On Day 58, when larger bedforms are observed, the drag coefficients increased (0.0065). Observed roughness was 0.03m and 0.16m, on Days 51 and 58, respectively. Established models of bed roughness over-predict these values. Small sub-aqueous dunes were observed at the INDIA field site. This result is significant, as established theory predicted large dunes at this location. However, predictions appropriate to bedform dimensions provide reasonable estimates of the observed heights and lengths, most notably the prediction of van Rijn (1993), for small sub-aqueous dunes. The Scotian Shelf site (Ralph) exhibits suborbital wave ripples, which demonstrate a greater dependency on wave orbital diameter than is accounted for within existing predictions of suborbital ripples.
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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 | 0.000 | 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) | 0.001 | 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".