HYDROLOGY OF THE ST FRANCIS BAY MARINA, SOUTH AFRICA

SUMMARY

The results of an investigation into the physical characteristics of the St Francis Bay marina during April 1989, over a neap/spring tidal cycle are presented. The marina has two entrances into the adjacent Kromme estuary, and at that time an extensive area of intertidal sand banks had formed in front of the entrance closest to the estuary mouth. The tidal variations provide the dominant forcing on the system, and the sandbanks are shown to play an important part in the resulting current structures: in particular, flow was limited except at high tide, and the exchanges occurred primarily through the other entrance. Conditions in the nearby ocean also affect the marina, and cold water from an upwelling event rapidly penetrated the whole marina. This means that flushing and exchanges in the inner canals can be considered to be relatively efficient, though solar radiation served to heat up the water in the canals by up to 2°C.