Spatial and temporal variation of salinity stratification in a tropical estuary

Abstract

Longitudinal and vertical distribution of salinity field in the Vellar River Estuary (VRE) was investigated across the lower, mid and upper estuarine zone, monthly from January to December 2011. The hydrological survey of VRE revealed shallow bathymetry with a complex topography and a mean tidal amplitude of around 0.9 to 1 m. The depth-averaged tidal velocity had a magnitude that was observed with a maximum value of 0.56 m/s at the estuarine mouth and was indirectly proportional to the increasing distance from the mouth. The wind speed fluctuated from 1 to 4.1 km h-1 with a mean of 2.5±0.82 km h-1. The temperature ranged from 25.32 °C to 32.93 °C with a mean of 28.89±2.26 °C while salinity varied between 0 to 34 psu with a mean of 13±12.77 psu and negatively correlated with rainfall (r = -0.69; p = 0.04). A higher stratification number, i.e. ns ~ 1 at the lower estuarine zone indicated the formation of the salt wedge in the monsoon while during the rest of the year the estuarine water column was observed to be homogeneous. Wave height, tide and currents were estimated through 2D hydrodynamic models and they were significantly correlated with in-situ data. Recorded seasonal variation in salinity stratification of VRE from the present work reflected on shaping the primary governing factors on estuarine circulation at spatial and temporal scales.