Submarine dune field morphodynamics in a tidal inlet: San Blas, Argentina

• Published in: Latin american journal of aquatic research Vol. 40; no. 1; pp. 42 - 52
• Main Authors: Cuadrado, D G, Gomez, E A
• Format: Journal Article
• Language: Spanish
• Published: 01.01.2012
• Subjects: Marine; PSW, Argentina, Buenos Aires, Anegada Bay
• ISSN: 0718-560X
• DOI: 10.3856/vol40-issue1-fulltext-5

The morphology of a submarine dune field developed in a tidal inlet that connects the Argentinean continental shelf with Anegada Bay (southern Buenos Aires province) was studied. The sediment circulation was inferred from the differential displacements of the bedforms evaluated by comparing consecutive surveys. An echosounder and a Phase Measuring Bathymetric System (PMBS) called GeoSwath were used to obtain a detailed submarine morphology. Large dunes, with heights between 4.5 and 5.0 m and from 100 to 120 m separating them, were present near the southern limit of the dune field at 24 m depth. These dunes move towards the outer part of the channel at a speed of 18 to 75 m year-1. At the northern end of the dune field, at 21 m depth, the dunes are smaller, being 2.0 to 2.5 m in height and separated by 40 to 80 m. The smaller dunes move towards the interior of Anegada Bay at 18 to 36 m year-1. The distribution of the water flow in the entire water column was obtained through a perpendicular profile of the channel by means of an ADCP. Maximum current speeds were 2 m s-1, and were found during flood tide. The results obtained indicate a circulatory transport model of sedimentary sands, with the formation of ebb and flood deltas at both ends of the deep inlet throat, which lacks of unconsolidated sediments.Original Abstract: Se estudio la morfologia de un campo de dunas submarinas desarrollado en una entrada de marea que conecta la plataforma continental argentina con bahia Anegada (sur de la provincia de Buenos Aires). Se infiere la circulacion sedimentaria a partir del desplazamiento diferencial de las geoformas medido en relevamientos consecutivos. Como parte de la metodologia se utilizo un ecosonda y un sistema batimetrico por medicion de fase (SBMF) denominado GeoSwath que permitieron obtener la morfologia submarina en detalle. Se observaron dunas grandes sobre el limite sur del campo de dunas con altura entre 4,5 y 5,0 m y espaciamiento entre 100 y 120 m, a profundidades de 24 m, que se desplazan hacia el exterior del canal a una rapidez entre 18 y 75 m ano-1. Hacia el limite norte del campo, a 21 m de profundidad las dunas eran de menor magnitud, entre 2,0 y 2,5 m de altura y espaciamiento entre 40 y 80 m, y se desplazaron a una rapidez entre 18 y 36 m ano-1 hacia el interior de bahia Anegada. Se obtuvo la distribucion del flujo de agua en toda la columna, en un perfil perpendicular al canal relevado, mediante ADCP. Los valores maximos de rapidez de corriente fueron durante la marea creciente, alcanzando 2,0 m s-1. Los resultados obtenidos permiten definir un modelo circulatorio de transporte de sedimentos arenosos, con la formacion de un delta de marea de flujo en la cabecera de la entrada de marea y un delta de reflujo en el limite del dominio oceanico, unidos por una garganta de marea profunda, exenta de sedimentos inconsolidados.