CIRCULATION PATTERN IN A MEANDERING TIDAL CHANNEL, BAHIA BLANCA ESTUARY, ARGENTINA

PERILLO, GERARDO M.E.; ALVAREZ, LAURA I.; VITALE, ALEJANDRO; CIPOLLETTI, MARINA; GREGORI, MAURO LÓPEZ; ALBERDI, ERNESTO

Puerto Madryn

Conferencia; TIDALITES 2015; 2015

The inner portion of the Bahía Blanca Estuary (Figure 1) coincides with the final reach of the Canal Principal where the tidal wave tends to converge and it is most evident the hypersincronizity of the estuary. The tidal range in this area reaches up to 4 m in scizigy whereas at the mouth of the estuary, more than 70 km from the study area, tidal range is of the order of 2.2 m. The study area is also one of the most strategic sectors in the estuarial ecosystem since it is where the trophic chain of the estuary starts due to winter phytoplankton (Guinder et al., 2009). Consequently, the main aim of the study is to define the circulation pattern of the tidal currents during the same period of the year. Calm or very low wind velocities and scarce precipitation characterize this season. Two field cruises were made, one on July 4th and 5th and another on 11th and 12th, 2011 corresponding to neap and spring tides, respectively. On each cruise, vertical profiles of current velocity and direction were made in a total of 7 transects transversal to the Canal Principal separated about 1000 m between them. Transect location and name are shown in Figure 1. Data was gathered employing an Acoustic Doppler Current Profiler (ADCP) RDI Teledyne 600 kHz onboard the oceanographic boat IADO IV and located with a DGPS-RTK Sokkia which base was established in Puerto Cuatreros (Figure 1) at the center of the study area. Cells were 50 cm with a sampling frequency of 1 Hz. At the end of each measurement cycle, vertical profiles of conductivity, temperature and suspended sediment concentration employing a MiniCTD InterOcean with an OBS adapted were taken at a station located at the center of the central transect. We filtered the original data to partially suppress the intrinsic turbulence of the tidal currents since the required data was for the general circulation pattern. The filtering included vector averaging all vertical profiles within a 10 s range. The resulting vertical profile was defined for the time and location of the middle profile of the range. Based on the space-time interpolation procedure developed by Perillo and Piccolo (1991, 1993, 1998) and Perillo et al. (1999), we transformed the original data taken at diverse times and locations along a transect and for a whole tidal cycle. This methodology allows to interpolate them to standard positions and time working in a non imensional space.