Flow characteristics of Combarjua canal connecting Mandovi & Zuari estuaries

Abstract

A comparative study of the tidal flow patterns at the two terminals of the Combarjua canal which connects the estuaries of the two rivers, Zuari and Mandovi, is presented. It is shown from the analysis of tidal currents and vertical tides together with the variations in salinity over complete tidal cycles that the postmonsoon flow pattern in Combarjua, when there is little freshwater discharge through the river Zuari and very little through Mandovi, is controlled primarily by the tidal conditions at the Zuari side of this connecting canal. The distribution of the tidal energies reaching the two ends of the canal is shown to be 77 and 23% respectively at the Zuari and Mandovi openings whose relative magnitudes appear to be the deciding factors for the flow characteristics of the canal. Differences in the salinity at the Zuari and Mandovi ends of the canal suggest that the larger volume of freshwater storage in the Mandovi river system may account for the appreciable lower salinity at the Mandovi side of the canai. The salinity gradients in the Combarjua canal reveal a net salinity influx from the Zuari side to the Mandovi side of the canal and to the upper reaches of the Mandovi river. Variations in the suspended sediment loads in the surface and near bottom waters in relation to the tidal stages, during the postmonsoon period, are also discussed. The sediment loads do not show much dependence on the speeds of the tidal current but they seem to be a little dependent on the salinity of the waters. This study suggests that the problems of sedimentation and pollution through waste disposal in this canal should be viewed in the context of the circulation features of the canal.