Comparative hydrodynamics of a sub-tropical salt-wedge estuary and a tributary

The objective of this study is to compare the physical characteristics of circulation, salinity structure and transport in the Itajai-Acu and Itajai-Mirim estuaries. Due to its importance, the Itajai-Acu estuary has been studied in the last decade. However, its main tributary, the Itajai-Mirim has never been assessed, especially as an opportunity to comparatively investigate the flow behavior of salt wedge estuaries with different widths and depths. Field data were acquired during two campaigns that covered the complete semi-diurnal tidal regimes during spring and neap tides. Water level, total transport volume, current and salinity were recorded hourly and synoptically at cross-sections in each estuary. The campaigns were conducted during a prolonged period of low river discharge. The tidal range during the spring and neap tide campaigns were of approximately 1.2 and 0.4 m, respectively. At the Itajai-Acu and Itajai-Mirim cross-sections, the peak ebb and flood currents were -0.8 and -0.6 m s(-1) and 0.8 and 0.4 m s(-1), respectively, during the spring tide campaign, and classified as well mixed and highly stratified estuaries, respectively. During the neap tide campaign, both estuaries were classified as salt wedge. The dominant mechanism was the salt transport by advection due to fluvial advection in both estuaries and campaigns. The landwards salt transport, which resulted from dispersive processes, was only important during neap tide for the Itajai-Acu estuary.