Eintrag weiter verarbeiten
Les cordons de galets de la Baie des Anges : histoire environnementale et stratigraphique ; évolution morphodynamique récente en réponse à des aménagements/The gravel barriers of t...
Gespeichert in:
| Zeitschriftentitel: | Géomorphologie relief processus environnement |
|---|---|
| Personen und Körperschaften: | , , |
| In: | Géomorphologie relief processus environnement, 4, 1998, 2, S. 167-187 |
| Format: | E-Article |
| Sprache: | Französisch |
| veröffentlicht: |
PERSEE Program
|
| Schlagwörter: |
| Zusammenfassung: | <jats:p>Abstract The gravel barriers of the Baie des Anges (French Riviera) protect the densely developed area of Nice against marine flooding. The general setting of these barriers is that of a steep coastal margin and shelf, and a fetch-limited, low wave-energy, almost tideless environment. In terms of sequence stratigraphy, these gravel barriers, which have yielded radiocarbon ages ranging from 3000 yr B.P. to Present, are part of a highstand systems tract comprising essentially gravelly river-channel and finer-grained floodplain, delta-plain and nearshore deposits. The local sea-level curve shows a strong slow-down in the Holocene transgression at around 4000 yr B.P. This change coincided with active upland erosion by mountain streams exhibiting catastrophic flow regimes that resulted in downstream bedload channel aggradation and seaward flushing of gravel clasts. The present gravel barriers, which may have been formed and dismantled successively during the eustatic transgression, are an outgrowth of these bioclimatic conditions and of the change from transgression to stillstand. Once gravel supply from river mouths to the littoral drift system became efficient, the gravel barriers became consolidated by bi-directional longshore drift with changing drift termini, in response to short, poorly refracted waves coming from a wide zone spanning east to south-west. The barriers seem to have been morphodynamically stable forms as a result of their highly gravelly composition, relative sea-level stability, and the almost tideless, low energy and fetch- limited hydrodynamic setting of the bay. Stability was enhanced by crestal buildup, a drift-aligned plan-form configuration that enabled longshore transfer of fluvial sediment to make good losses to the steep nearshore shelf, and a textural organisation that favoured segregation between coarse and fine clasts, leading, in the long run, to relative enrichment in coarse clasts and resistance to change. The barrier sediment budgets were balanced, with gains from the coastal rivers compensating for the losses to the steep nearshore zone, which also considerably limited progradation. Over the past century, human activities have resulted in the destabilization of the barrier beach sediment budgets, initiating a phase of slow, uneven erosion and textural disorganisation. To counter this erosion, gravel nourishment has been practised on certain portions of beach in the last twenty years. Optimization of these periodic nourishment campaigns however requires not only a fine understanding of the environmental context and mechanisms of morphodynamic development of these gravel barriers but also of the hydrodynamic processes involved in their breakdown. </jats:p> |
|---|---|
| Umfang: | 167-187 |
| ISSN: |
1266-5304
|
| DOI: | 10.3406/morfo.1998.953 |