Tidal asymmetry in the Mandovi and Zuari estuaries, the West Coast of India

Abstract

Harmonic analysis of the observed and simulated tides in the Mandovi and Zuari estuaries along the west coast of India was carried out. Tidal constituents derived from this process were analyzed to study the tidal asymmetry in these estuaries. Sea level observations during March-April 2003 at 13 stations in the Mandovi and Zuari estuaries were used for the harmonic analysis. Simulations of tides were carried out using a hybrid network numerical model. The model could well simulate the amplitude and phase of five major tidal constituents (K sub(1), O sub(1), M sub(2), N sub(2), S sub(2)) in almost all stations in the Mandovi and Zuari estuaries. Both observations and simulations show that the amplitude and phase of major diurnal and semidiurnal constituents increase toward the upstream regions. The increase of this predominant species toward the upstream regions shows that the Mandovi and Zuari estuaries are not frictionally dominated estuaries because amplification due to geometrical effects cancels the decay in amplitude due to friction. The rapid increase of the first and second harmonics of M sub(2) and compound tides inside the estuaries shows the nonlinear response of the Mandovi and Zuari estuarine systems to tidal forcing. The M sub(4)/M sub(2) amplitude ratio indicates that the tide is subjected to more asymmetry in the Zuari than that in the Mandovi estuary. The increase of the first harmonic of M sub(2) and decrease of relative surface phase (2M sub(2) - M sub(4)) inside the Mandovi and Zuari estuaries show that these estuaries are flood dominant estuaries.