HYDROLOGY OF THE ST-FRANCIS BAY MARINA, SOUTH-AFRICA

The results of an investigation into the physical characteristics of t he St Francis Bay marina during April 1989, over a neap/spring tidal c ycle are presented. The marina has two entrances into the adjacent Kro mme estuary, and at that time an extensive area of intertidal sand ban ks had formed in front of the entrance closest to the estuary mouth. T he tidal variations provide the dominant forcing on the system, and th e sandbanks are shown to play an important part in the resulting curre nt structures: in particular, flow was limited except at high tide, an d the exchanges occurred primarily through the other entrance. Conditi ons 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 rel atively efficient, though solar radiation served to heat up the water in the canals by up to 2-degrees-C.