Study of the characteristics of currents and water-level variations in the Cochin estuary reveals, for the first time, unique signatures of mixed standing-waves in the southern region. Analysis of the simultaneous water-level data generated at the mouth of the estuary, located about 45 km upstream, showed very little dissipation had taken place in the tidal amplitudes, implying that tides are amplified because of a physical barrier. The amplitudes of the major tidal constituents O1, K1, M2, and S2 were 87, 87, 83, and 79%, respectively, of the values close to the sea. The M2 tide was found to be the maximum, followed by the K1, S2, and O1 constituents. Sea level was found to be largely forced by the astronomical tides at both the locations. The nontidal time series at the two locations correlated strongly, with the percentage of the variance explained by the relationship being about 82.3%. Currents and their displacements were found to be of low magnitude but revealed significant spatial variability, even though they were closely spaced. As compared with the cross-shore currents, the alongshore currents were highly coherent, with clear signatures of tidal forcing. Further, tidal analysis of synchronous data on various parameters—water level, alongshore and cross-shore currents, temperature, and salinity—revealed the relative dominance of the various tidal constituents. The water temperature peaked during late afternoon, suggesting solar forcing, whereas salinity variation, though quite low in range, showed signatures of tidal forcing. A scatter plot of water level and spatial average of alongshore currents revealed correlations of minima in overtide velocity amplitudes. The magnitude of the currents was very small and not proportional to the tidal heights observed. Intense mixing is closely related to the horizontal velocity shear, which causes mixing sufficient to destratify the water column. Resonance of the M2 tidal wave may be possible because of the length and depth relation in the estuary, and the results suggest overtides are the causative factor.
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