Evolution of Coastal Defence Structures and Consequences for Beach Width Trends, Québec, Canada
Bibliographic record
Abstract
Bernatchez, P., and Fraser, C., 2012. Evolution of coastal defence structures and consequences for beach width trends, Québec, Canada.Over recent decades, amplification of coastal erosion, coupled with the expansion of the built environment in Québec's maritime region, has led to a significant increase in defence structures. On unconsolidated coasts, severe beach width reduction was noted following the construction of hard engineered structures when compared to beaches with no such constructions. Beaches in the sectors of Sept-Îles and Percé, where shorelines have been modified by rigid defence structures parallel to the coast, have had a reduction in width of 85% and 44%, respectively. In some places, beaches have almost completely disappeared. On low-lying sandy coasts, although an immediate width reduction of 19% to 27% is attributable to the encroachment of the structures on the upper beach, most of the width reduction (74% to 81%) is due to erosion caused by the reflective nature of the defence structures. The effects of the defence structures on the sediment deficit of the beaches are much worse for coasts with a high level of sediment transit. Such consequences significantly diminish coastal resilience to climate change and storm events because, under such circumstances, beaches cannot absorb nearly as effectively the energy of storm waves. A look at the historical record of coastal construction shows that rigid defence structures parallel to the coast have not only led to beach erosion, but they have also limited the shoreline progradation process. The sediment budget variations of beaches on natural coasts correlate well with relative sea-level trends. An average decrease in beach width of 43% due to sea-level rise was measured on natural coasts. However, the results show that the reaction of a beach to an increase in sea level is much more complex than a simple translation of its equilibrium profile. Beach width is a very good geomorphological indicator for evaluating long-term trends with respect to the sediment budget of coastal systems, as well as evaluating the relative importance of natural and anthropogenic causes of the sediment deficit of beaches.L'amplification de l'érosion côtière jumelée à l'accroissement du cadre bâti au Québec maritime a engendré une augmentation importante des structures de protection durant les dernières décennies. Les ouvrages de protection rigides ont entraîné une réduction de la largeur des plages sur les côtes meubles comparativement aux plages naturelles sans artificialité. Les plages dont la ligne de rivage est artificialisée par une structure rigide de protection ont connu une réduction de leur largeur de 85% et de 44% respectivement pour les régions de Sept-Îles et de Percé. La plage a presque complètement disparu à certains endroits. Sur les côtes basses sablonneuses, la réduction totale de la largeur des plages est attribuable à une réduction instantanée de 19 à 27% par l'empiétement des ouvrages sur le haut de plage, mais surtout à l'érosion (74% à 81%) en raison de la nature réflective des ouvrages de protection. Les effets des ouvrages de protection sur le déficit sédimentaire des plages sont beaucoup plus néfastes pour les côtes avec un fort transit sédimentaire. Ces conséquences diminuent de manière significative la résilience côtière aux changements climatiques et aux événements de tempête puisque les plages ne peuvent plus absorber de manière aussi efficace l'énergie des vagues de tempête. Le bilan de l'évolution de l'artificialité de la côte indique que les structures rigides de protection ont eu pour conséquence non seulement de provoquer une érosion des plages, mais aussi de limiter le processus de progradation de la côte. Une variabilité dans le bilan sédimentaire des plages sur des côtes naturelles a aussi été mesurée en fonction de la tendance du niveau marin relatif. Une diminution d'une moyenne de 40% de la largeur des plages a été mesurée sur des côtes naturel
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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 | 0.001 | 0.002 |
| Meta-epidemiology (narrow) | 0.001 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.001 |
| Bibliometrics | 0.002 | 0.007 |
| Science and technology studies | 0.003 | 0.001 |
| Scholarly communication | 0.002 | 0.001 |
| Open science | 0.001 | 0.001 |
| Research integrity | 0.000 | 0.001 |
| Insufficient payload (model declined to judge) | 0.008 | 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".