Interactions of river discharge and tidal modulation in a tropical estuary, NE Brazil

Abstract

Observations of thermohaline properties and currents were undertaken in the Curimatau´River estuary (6°18¢S), Rio Grande do Norte state (RN), Brazil, during consecutive neap-spring tidal cycles in the austral autumn rainy season. Highly asymmetric neap tide along channel velocities (À0.4 to 0.9 m s À1 ) and highly stratified conditions were generated by an increase of the buoyancy energy from the freshwater input (R iE %5.6). During the spring-tidal cycle the river discharge decreased and the longitudinal velocity components were higher, less asymmetrical (À0.8 to 1.1 m s À1 ) and semidiurnal, associated with moderately stratified conditions (R iE %0.1) due to the increase of the kinetic tidal energy forcing mechanism. The overall salinity variation from surface to bottom during two tidal cycles was from 20.5 to 36.3 and 29 to 36.7 in the neap and spring tide experiments, respectively; in the last experiment, the tropical water (TW) mass intrusion was enhanced. The net salt transport reversed from down to up estuary during the neap and spring tide experiments, respectively, varied from 6.0 to -2.0 kg m À1 s À1 , an indication of changes in the main forcing of the estuary dynamics. Evaluation of a classical steady analytical model, in comparison with nearly steady experimental vertical profiles of velocity, shows an agreement classifiable as reasonably fair.

Comparative analysis of rating curve and ADP estimates of instantaneous water discharge through estuaries in two contrasting Brazilian rivers

“…This behaviour was observed by Miranda et al (2005), in a study performed in the Curimataú River, where the author shows that the salinity ranges from 20 to 36 in the period of major fluvial discharges and from 30·2 to 30·7 in the dry season. This behaviour shows a major amplitude in the variation of salinity, showing an increased influence of coastal waters (CW) during periods of lower fluvial discharges (dry season).…”

“…The tidal co‐oscillation at the estuaries' mouths is classified as meso‐tidal and semi‐diurnal according to its height and periodicity, respectively, ranging between 1·1–1·4 and 1·8–2·0 m in neap and spring‐tide periods, for the Contas and Jaguaribe Rivers, respectively (Dias, 2007; Dias et al , 2007). Many studies conducted in tropical estuaries (Cunha, 1982; Medeiros and Kjerfve, 1993; Araujo, et al , 1999; Miranda et al , 2005) observed a higher tidal influence during dry period, where the estuaries were controlled for a semi‐diurnal barotropic tide. Nicolite et al (2009) observed that during lower discharges water level variation in the estuarine channel is due to the co‐oscillation of the astronomical tides and/or meteorological tides in the estuary of the Paraiba do Sul River.…”

Dynamics of a temperate fluvial estuary in early winter

“…A similar effect was found by [13] in studying the dynamics of a tropical estuary, the Curimataú River, Brazil.…”

Continental shelf water masses off the Jaguaribe River (4S), northeastern Brazil

“…Beyond isopycnic 20 (s θ ≥20), there was a marked presence of the coastal water masses (CW). This type of distribution was described by Miranda et al (1998Miranda et al ( , 2002Miranda et al ( , 2005 as a classical distribution of water masses in estuarine systems. Table 3 Values of temperature (1C) and salinity characteristics of the respective water masses observed in the study area.…”