Modelling tide-driven currents and residual eddies in the Gulf of Kachchh and their seasonal variability

Tide-driven currents in the Gulf of Kachchh (GoK) have been studied using MIKE21 hydrodynamic model. The results are validated with measured currents for three different periods characterized by different wind fields. Comparison of model results showed very good agreement with the measured currents. The study suggests that though the currents of GoK are predominantly tide-driven, they respond significantly to the seasonally changing wind system. Strong southwesterly winds enhance the flood tidal currents by about 20% but reduce the ebb tidal currents by about 20% during June-July. The currents intensify during NE monsoon period as well as SW monsoon period when the winds become stronger. However, the currents are comparatively weak during pre-monsoon transition. Irregular topography of the western gulf slows down the tidal wave propagation and induces a phase shift. Tidal residual currents computed from the model results exhibit the presence of three eddies in the western gulf. The tide-topography interaction could be responsible for generating eddies in the residual flow field. It is possible that these eddies could effectively decrease the flushing rate of materials discharged in the upstream gulf, and subsequently increase their residence time. The hydrodynamic modelling setup forms a base for future ecological modelling endeavours planned for the gulf in order to reduce stress on the ecosystem especially in the sensitive areas such as the Marine National Park and Marine Sanctuary.