Preliminary results in the San Blas submarine morphology (Argentina).

CUADRADO D.G.; GÓMEZ E.A.; RANIOLO A.

Santa Fe

Simposio; 6th Symposium on River, Coastal and Estuarine Morphodynamics; 2009

International Association on Hydraulic Engineering and Research (IARH)

Bahia San Blas is located at the southern part of the Anegada Bay (Buenos Aires Province) and is characterized by a broad channel, 2.5 km width that separate Gama Island from the continent. Not many studies have been taken in the area. Most of them were related to geomorphologic investigations in the littoral zone, which studied the characteristic gravel ridges present in the zone. There is only one research referred to the oceanographic characterization (Alvarez and Rios, 1988) which had obtained the general bathymetry and the dynamics in some specific position within the channel. Recently, a detailed bathymetry was carried out over a zone of 50 km2. The results show steep flanks towards the mouth of the channel and an extended flat bottom over 700 m across the channel with 28 m-depths. To the inner part of Bahia Anegada, not far from Los Pocitos, the depth diminishes up to 15 m. Here, there are sand banks exposed during low tides. The littoral sediment transport had built a sand spit connected to the shore at Punta Ramirez, suggesting the occurrence of a net longshore transport toward the channel mouth. Over a zone of 1.5 km2 characterized by a field of subaqueous dunes, a Swath Bathymetry System “GeoSwath Plus” from GeoAcoustics Lt. was employed to determine detailed dunes morphology, giving also the possibility to measure dune’s migration rate in a future survey. Large dunes with spacing between 40-80 m and heights of 2.5 m were identified at 21 m-depth. In the deeper zones higher dunes occur, reaching values of 4.5-5 m-height at around 24 m-depths. Most of them exhibit a symmetrical profile and are covered with smaller bed forms characterized by 0.5-1 m-height. Also, tidal currents were measured using an ADCP mounted on a ship. Tracks across the channel were carried out over a whole tidal cycle, obtaining currents speed and direction profiles. The results indicated that the maximum velocities reach 2 ms-1 during the flood. This high dynamic in the area is reflected also in the coarse beach sediments composed by gravel and coarse sand from Bahia San Blas towards the mouth of the channel.