Geomorphology, ichthyofauna, water quality and aesthetics of south african estuaries

Abstract

The South African 3 000 km coastline has approximately 370 outlets to the sea ranging from small coastal streams to large permanently open tidal estuaries. The current state of scientific information on the vast majority of these systems, however, is virtually nil. As part of a national program to assess the state of South Africa’s estuarine environment, basic surveys were conducted on these systems during the period 1992 to 1999. This included ichthyofauna (fish), water quality, and geomorphological and aesthetic observations. Some 67% of South Africa’s ‘estuaries’ have been surveyed to date. This baseline data has been analysed and synthesised to render it understandable to the non-specialist but at a sufficiently high level to inform potential end users of the state of South Africa’s estuaries. A conceptual classification of the geomorphic variability among South Africa’s estuaries has been produced. Several systems particularly on the west coast were not considered estuaries either due to their small size, their ephemeral nature, or because they were essentially isolated. Six basic estuary types were identified. These were divided into normally open and normally closed systems. Two types of normally closed estuaries were recognised. These were systems where the water level was typically perched above sea level and those where the water level was approximately at sea level. In this report, however, the normally closed estuaries were sub-divided into small, medium, and large systems based on surface area. The normally open systems were divided into barred and non-barred estuaries. Two types of permanently open barred estuaries were recognised: river-dominated and tide-dominated systems. In this report the two types of normally open barred estuaries were not identified but were sub-divided into small and medium to large systems based on their mean annual runoff.