Variability in tidal harmonics of the coastal and estuarine waters of Goa during winter monsoon and spring inter-monsoon

Abstract

Harmonic analysis was carried out with simultaneously observed tide elevation in the coastal and estuarine regions of Goa. The tide elevations were consistent along the coastal stretch of 80 km; however, significant variations were obtained inside the estuarine channels. In both estuaries, the increase in tide elevation was observed from mouth to head, also reflected in the major harmonic constituents. M2 was found to be the principal constituent, which was consistent in the coastal region. The maximum M2 amplitude of 66.27 cm was recorded at Pontemol (upstream of Zuari estuary) during spring inter-monsoon. The increase of M4 tide in both the estuarine channels confirms the non-linearity of the system. The phase lag of MS4 from the forcing tides of M2 and S2 indicated flood dominance of the system. The tidal current velocities were well-reflected by the tidal ellipse. Our datasets do not reflect significant changes in tidal dynamics in the two seasons. Instead, it was noticed that a small shift in bottom topography could lead to a considerable difference in the tidal dynamics of the system, which is reflected in the estimated form number and tidal skewness values. The study puts up an effort to compare the earlier harmonics with the present ones to infer the decadal evolution of the astronomical constituents in the estuarine stretch of Goa. Furthermore, the association between the larger wave with high water could indicate about the flood-risk of this region.