Wind-driven estuarine turbidity maxima in Mandovi Estuary, central west coast of India

Abstract

Systematic studies on the suspended particulate matter (SPM) measured on a seasonal cycle in the Mandovi Estuary, Goa indicate that the average concentrations of SPM at the regular station are approx. 20mg/l, 5mg/l, 19mg/l and 5mg/l for June-September, October-January, February-April and May, respectively. SPM exhibits low-to-moderate correlation with rainfall indicating that SPM is also influenced by other processes. Transect stations reveal that the SPM at sea-end stations of the estuary are at least two orders of magnitude greater than those at the river-end during the monsoon. Estuarine turbidity maximum (ETM) of nearly similar magnitude occurs at the same location in two periods, interrupted by a period with very low SPM concentrations. The ETM occurring in June-September is associated with low salinities; its formation is attributed to the interactions between strong southwesterly winds (5.1-5.6ms sup(-1)) and wind-induced waves and tidal currents and, dominant easterly river flow at the mouth of the estuary. The ETM occurring in February-April is associated with high salinity and is conspicuous. The strong NW and SW winds (3.2-3.7ms sup(-1)) and wind-driven waves and currents seem to have acted effectively at the mouth of the estuary in developing turbidity maximum. The impact of sea breeze appears nearly same as that of trade winds and cannot be underestimated in sediment resuspension and deposition.