Spatial tidal asymmetry of Cochin estuary, West Coast, India

An intensive one-month long observational campaign of tides and currents during dry season were used to describe the tidal dynamics and the spatial evolution of tidal asymmetry in Cochin estuary. The estuary is described as hyposynchronous since tidal amplitude and currents get attenuated towards upstream through frictional dissipation. The results showed that the tidal momentum balance along the main axis of the channel was dominated by pressure gradient and friction. The influence of advection was prevalent near the inlets and friction was greatest in the shallow upstream regions. Higher harmonics were generated in the estuary through nonlinear friction and advection causing tidal distortions. Being a mixed predominantly semidiurnal tidal regime, tidal asymmetry was quantified in terms of sample skewness to examine the spatial evolution in the total asymmetry. The principal astronomical tides (M2, K1 and O1) interacted to engender flood dominance at the inlets. The compound tides and overtides generated inside the estuary were found to either augment or transform the asymmetry imposed by the principal tides. The study showed that friction causes flood dominance at the northern inlet (Munambam) and in the shallow regions of the upstream during dry season. In striking contrast, the Cochin inlet and the adjacent harbor area turned to be ebb-dominant. These findings have implications for management and sediment transport mechanisms within the estuary.