Circulation pattern in a tidal channel influenced by tributary channels and adjacent tidal flats

摘要

The main objective of the present paper was to determine the general circulation pattern and also evaluate how the tributary channels and the extensive tidal flats along both banks on the Canal Principal influence the pattern. Current velocity and direction data were obtained near the head of Canal Principal of the Bahía Blanca Estuary during a spring tidal cycle with a total of seven transects transversal to the channel. Geomorphologic and hydrodynamic characteristics of the study reach were made with an Acoustic Doppler Current Profiler (ADCP) mounted on a ship and positioned with a DGPS-RTK. The tide and wind data were obtained by means an Estación de Monitoreo Ambiental Costero (EMAC) located at Puerto Cuatreos, at the center of the study reach. The ebb currents are stronger although the flood stage is longer; however, it cannot balance the former resulting in an ebb-dominated circulation. Inside the study region, the circulation is affected by the channel curvature. The ebb current has a predominant role in modeling the meander. Most of the transects located between Puerto Cuatreros and the Maldonado Channel show a nucleus of higher velocities in the center, decreasing in the vicinity of the channel bed and the flanks. Near low-tide slack water some dissimilarities were observed developing a two-layer stratification of the flow, which although it has been reported before in the estuary, never measured in detail. During ebb, from the analysis of the data in the area of channel confluences, a shear layer was observed due to the interaction between the main stream and the discharge from the tributary channels. Meanwhile, during the flood, decrease in the speed and a deviation of the main flow direction, were detected as a consequence of the flow separation due to the presence of the tributary and the tidal flats (specially in the later part of the flood). In the area of Puerto Cuatreros wharf, a current acceleration towards the center of the channel was detected, producing a vertical flow adjacent to the wharf. Finally, using the backscatter intensity data provided by the ADCP, a qualitative analysis of the sedimentary dynamic over the study region was made.