Salinity and suspended sediment transport in a shallow estuary on the east coast of India

Abstract

Velocity, salinity, tidal depth and suspended sediment concentrations were monitored at the two stations located at the mouth and head of the Muthupet estuary during the spring and neap tides of post-monsoon, pre-monsoon and monsoon seasons. There was a pronounced seasonal variation in the salinity and suspended sediment concentration during the study period. The total transport of salt at the station near the mouth varied between 4.78 kg/s/m and 0.038 kg/s/m. The transport of suspended sediments was in the range of 0.021 kg/s/m and 0.121 kg/s/m. The direction of transport of salt and suspended sediments also varied over a seasonal scale. The transport of salt and suspended sediments occurred in the downstream direction during the post-monsoon and monsoon, while it was in the upstream direction during the pre-monsoon. Fluvial advection was identified as the main controlling factor in the transport of salt and suspended sediments. The formation of salt plug during the pre-monsoon affected the transport of salt; the transport of salt was from the location of salt plug to the upstream and downstream directions. The spatial variability in the transport of suspended sediments was evident, with higher transport at the downstream station than that at the upstream station. The transport of salt was correlated with the concentration of Fe in the estuary obtained from previous studies. Further, it was observed that the concentration of Cd and Cu was dependent on the resuspension of sediments due to tidal action. The study proved that all the suspended sediments transported towards the upstream from the downstream reaches do not reach the upstream station, but are removed from the water column; the transport of suspended sediments were correlated with the settling velocity established from previous studies.