Abstract

ISLA, Federico I et al. Dinámica morfosedimentaria de playas de arena y grava de la Barrera Austral: Mar del Sud, Arenas Verdes y Costa Bonita. Rev. Asoc. Argent. Sedimentol. [online]. 1997, vol.4, n.1, pp.15-24. ISSN 1853-6360.

Four profile series (three on each beach) were carried out in the beaches of Mar del Sud (MS), Arenas Verdes (AV) and Costa Bonita (CB), within a much important study on the sedimentary dynamics of the Southern Barrier of Buenos Aires. These 4 series comprise one year of measurements (April, August, November, 1994, and March 1995). The distance between profiles was 100 m and elevations were taken every 5 m from the backshore to the breaker zone. MS and AV are natural beaches; they differ in their beach gradient 3-4.5% and 5-8% respectively). MS beach is stable due to the stabilizing effect of the La Tigra and La Carolina inlets. CB (5-7.6%) is a beach modified by rigid and straight groynes construction, and sand mining that continues to present days. The principal characteristics of AV and CB are their gravel composition in the sublittoral zones, fine to medium sand in the foreshore, and medium to coarse at the backshore. A significant portion of the gravels are of volcanic origin, and related to the reworking of Holocene beaches from the area (CB). In AV there is a significant seasonal variability, probed by MANOVA tests, between fine, and coarse and very coarse sand. In MS, fine sand dominates while very coarse sand dominates at the breaker zone. Annual budgets were erosive for MS (-930 m³) and AV (-17,000 m ³), while accumulative for CB (20,000 m³). Gravel and sand availability at these beaches permits armouring phenomena, either at the backshore as wind granule ripples, or at beach cusps, induced by swash and backwash flows.

Keywords : Sedimentary dynamics; Sand and gravel beaches; Southern Barrier.

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