On the Salinity Distribution Induced Mixing at the Mouth of the Estuary

Salinity is an essential parameter in estuaries because it determines the mixing process and distribution of biota in the estuary ecosystem. In the paper, we investigate the dynamics of salinity distribution in the Dumai estuary. Salinity and tidal data observation were carried out during the transitional season around the mouth of the estuary. We get the salinity time series data in a tidal cycle. We observed that the Formzhal number is about 0.239, indicating that the tidal type in Dumai estuary waters is mixed directional, tending to double a day, with the highest and lowest tides in the Dumai estuary being 1.26 and 0.47 m, respectively. The salinity variability due to tides was studied by harmonic analysis, while the spatiotemporal distribution was studied using an analytical solution developed by previous researchers. The results show the presence of time lag between tidal elevation and salinity variation. Low tide and salinity, which indicate the effect of river discharge, are significant. This study further indicated that high salinity occurs during strong mixing conditions. It implied that the high salinity from the offshore entrance to shallower waters allowed for mixing processes. This paper ends with a comprehensive discussion of the vertical distribution of salinity at the mouth of the estuary.