Tidal flow structures and sedimentation in the lower Kowie estuary, Port Alfred, South Africa

Abstract

Marine sedimentation has occurred in the lower Kowie Estuary since the construction of the Royal Alfred Marina in 1989. It is believed that the problems have arisen because of the effectively greater flow area in the combined channels leading to a decrease in current speed in the estuary and a consequent deposition of the sediment. Investigations carried out in mid-1997 were directed at establishing the nature of the currents and sediments in the estuary and the marina, with a view to proposing possible management solutions.

The results demonstrate the subdivision of the flow at both entrances to the marina, on both the flood and ebb tides. Cross-sections measured from 1996 to 1999 indicate that an increasing percentage of the flow is passing through the marina. Sediment analyses support these conclusions, and suggestions are made for a novel technique to scour out unwanted sediment accumulations on the ebb tide.