MORPHODYNAMIC BEHAVIOR OF A TIDAL CHANNEL SYSTEM: BAHIA BLANCA ESTUARY, ARGENTINA.

VECCHI, L.G.; ALIOTTA, S.; GINSBERG, S.S.; GIAGANTE, D. A.

Vigo, Pontevedra. España

Conferencia; 4th Annual Conference of IGCP 526: Risk, Resources and Record of the Past on the Continental Shelf.; 2010

Universidad de Vigo, Grupo Geología Marina y Ambiental.

 Estuaries are highly dynamic structures where ebb currents are key in determining their morphological characteristics. Tidal channels within this environment are of pivotal importance as they determine flow dispersion. Both learning and predicting the evolution and sedimentary dynamics of estuaries are therefore greatly important to better understand these types of ecosystems. This investigation focuses on the study of the morphodynamics, erosive-depositational processes, and hydrosedimentological characteristics of a tidal channel system in Bahía Blanca estuary which is located in the south of the province of Buenos Aires, Argentina. The channels analyzed in this study, namely El Alambre, La Lista and Principal, are hydrodynamically-related. Different methods and techniques were used to study the geomorphological evolution, sediment circulation, and erosive-depositational processes. In particular, acoustic techniques such as echo sounder, side scan sonar; high resolution seismics (3.5 kHz), current measurements and bottom sediment sampling were used. In addition, marine sub-bottom seismoestratigraphic facies associated to the morphodynamics of the environment were analyzed. The channels studied are dominated by bidirectional currents (mesotidal regime) which behave as the principal agent ruling the processes occurring in them. The morphological features, dunes, point bar, elongated banks in the study area, as well as the current data obtained, are all indicative of ebb dominance. The sediment circulation model with highest transport values in El Alambre (0.08773 gr cm-1 sec-1) thus reveals export of material towards Principal channel. The tendency of evolution of the study area is due to a flank displacement which does not end in a significant deepening as a result of a lithological control of underlying material. In addition, it was observed that in El Alambre and La Lista there is a tendency to increase sinuosity in which depositationals are genetically-related to sedimentation resulting from the ebb current. In view of the morphological features and the dynamics of the study area, it can be concluded that El Alambre behaves as the principal pathway of this estuarine system and that La Lista behaves as its tributary.