Bathymetric flow rectification in a tropical micro-tidal estuary

Abstract

Temperature, salinity and current velocity data were recorded during the two principal atmospheric seasons affecting the tropical micro-tidal estuaries in the western Gulf of Mexico. Tropical micro-tidal estuaries in the western Gulf of Mexico share many characteristics, among them a narrow connection between the estuary and the adjacent continental shelf. Therefore, samples were taken during the dry (April 2009) and the rainy (July 2009) seasons, in order to elucidate the effect of the narrow connection between the estuaries and the continental shelf on flow dynamics. Due to the similarities between the tropical micro-tidal estuaries located in the western Gulf of Mexico, the Jamapa River estuary, a shallow estuary, with a narrow connection with the continental shelf and a ~5 m wide navigational channel, was used as a case study. During the dry season (April 15–17th, 2009) there was a surface horizontal displacement of the salinity and the temperature front of ~2 km, while during the rainy season (July 22–24th, 2009) the salinity and temperature gradients were mainly observed in the vertical at ~1 m depth. In this particular case, there was a marked difference between the northern and southern part of the estuary, due to the presence of a second river discharge (Arroyo Moreno), which discharges always stays in the northern part of the estuary (shallow area) owing to the influence of the navigational channel on fluid dynamics. Finally, a cyclonic recirculation was observed at the estuary mouth area. According to model outputs, the recirculation was observed when the ratio between the mouth and the estuary width were below 0.4, otherwise (>0.4) the recirculation was not observed. This should be a general behavior for all tropical micro-tidal estuaries located in the western Gulf of Mexico.