Tidal Circulation and Salinity Distribution in the Mandovi and Zuari Estuaries: Case Study

The Mandovi and Zuari are two tropical estuaries along the west coast of India, characterized by mixed tides with semidiurnal dominance and heavy fresh water influx during the southwest monsoon (June to September). Previous observations of tides in these estuaries show that the tidal effects in the upstream regions are subject to decay due to freshwater influx during the southwest monsoon. The longitudinal distribution of salinity in these estuaries undergoes large variations between the southwest monsoon and the dry season (February to May). The main objectives of the present study were to simulate the tidal circulation, the longitudinal distribution of salinity, and the freshwater influence on tides and the salinity distribution. Another objective was to study the intraseasonal variations of salinity during the breaks in the southwest monsoon. A hybrid network numerical model was used for the present study to simulate the tidal circulation and the salinity distribution in these estuaries. The model reproduced observed tides accurately during the dry and wet seasons. The model could reproduce the longitudinal distribution of salinity well during the dry season and the simulation of salinity distribution was reasonably well during the wet season. The simulated tidally averaged salinities over the M-2 tidal period for varying river discharges show that even a small freshwater influx can affect the longitudinal distribution of salinity to a great extent in this type of estuaries.