Seasonal variation of the salinity in the Zuari estuary, Goa

Abstract

The annual salt budget of the Zuari is examined. The characteristics of the estuary differ markedly from the low run off season during November-May to the heavy run off period of the southwest monsoon from June to October. During November-May the estuary is vertically mixed and the two processes controlling the transport of salt are run off induced advective transport out of the estuary, and tidally induced diffusive transport into the estuary. The magnitude of the latter is about 20% larger, leading to a salinity rise in the estuary. The diffusion coefficient has been estimated to be 233 ± 101 m2/sec. With the onset of the southwest monsoon, the run off increases dramatically, and the estuary loses about 75% of its salt during the first two months of the season. About 2/3 of this loss is recovered in the next two months when the run off decreases. Because the estuary is partially stratified during June-October, gravitational circulation is expected to play a role in addition to tidal diffusion and run off. The magnitude of its contribution has, however, not yet been determined.