Abstract

ISLA, Federico I et al. Villa Gesell: un desequilibrio sedimentario inducido por fijaciones de médanos. Rev. Asoc. Argent. Sedimentol. [online]. 1998, vol.5, n.1, pp.41-51. ISSN 1853-6360.

The city of Villa Gesell was urbanized on a coastal barrier of transverse dunes. In plan view, these dunes are also transverse to the coast oriented NE-SW. The fixation, forestation and urbanization of these dunes caused a change on the eolic sediment-transport pattern. The consequent sand scarcity induced a change in dune morphology: in certain places transverse dunes became parabolic. Littoral drift is to the north and of the order of 400,000 to 700,000 m3/year. Littoral fine sand moved dominantly landwards by wind action and was trapped in interdune depressions. The forested and urbanized dunes prevent that the winds from the west (“pamperos”) to return this sand to the coastal system. This microtidal coast has waves of  1,08 m average height and 9 seconds period. On the inner shelf, a sand-ridge field is composed of banks (5-7 m altitude) oriented in the direction of the storms originated in the  south. These sand ridges cause the refraction of long-period waves, and the formation of littoral cells; along the shoreline the breaker wave height could vary inducing sectors of erosion and deposition (cuspate coast). Vertical aerial photographs from 1957, 1967 and 1981 were used to recognize the shoreline behaviour. The foot of the dunes was stable at Villa Gesell city, but it receded at the south of the county (Mar Azul and Mar de las Pampas). This is explained by a selective aeolian transport of fine sand to the north (induced by the stronger winds from the south), where it is trapped at the vegetated dunes. The southern foredunes became therefore misfitted. Sedimentary budgets obtained from seasonal topographic surveys (from March, 1994 to August, 1997) recognize beaches of different dynamics (although we consider same beach lengths). The beaches from the north have less volume interchanges; the beaches from the south (Mar Azul and Mar de las Pampas) have a higher sediment dynamics. Coarse sands (shells and gravels) dominate in Villa Gesell beaches. They accumulate due to the reworking of Holocene littoral deposits (beaches and washovers) from the south. After episodic storms (usually coming from the south), shelly ridges move to the beach; linear shoals are supplying part of these shells.  The selective and biased transport of fine sand towards the vegetated dunes would have also caused this dominance of coarse lag sediments.

Keywords : Villa Gesell; Dunes; Management of barriers; Littoral erosion.

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