ESTUARIES IN SOUTH AFRICA

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SWARTVLEI ESTUARY: Catchment Characteristics

	Main Rivers and tributaries
	The total Swartvlei catchment area is 340km² with the Wolwe River system covering 125km², Hoekraal system 109km² and Karatara system 106km². (Ref 1)
	Dams

	River run-off
	The three catchments contribute about equal amounts of water to Swartvlei, the mean annual run-off from the Wolwe River amounting to 19,8x10⁶m², the Hoerkraal River 24,8 x10⁶m²and the Katara River 20,1 x10⁶m^2.An extra 1x10⁶m² can be added from minor streams and direct precipitation, resulting in an average total freshwater input of 66 x10⁶m³ from the catchment each year. Because of the all round rainfall pattern in the area there is no distinct seasonality in river flow. Flow is continuous throughout the year with occasional floods causing short-lived peak inflow periods. (Ref 1)
	Geomorphology

	Geology
	The geology of Swartvlei and its surrounding has been described by Martin (1962), the Department of Planning (1970) and Birch and Du Plessis (1977). Swartvlei is situated on a system of Quaternary sands which lie along the coast in an area known as the Wilderness-Knysna embankment. Sand ridges cemented by calcium carbonate form dune rock or aeolianite in this zone (Martin, 1962). Inland from these Quaternary sands is a 200m high Tertiary cut coastal platform through which the rivers flowing into Swartvlei have cut deep valleys. The Outeniqua Mountains , where these rivers originate, are made up of intensely folded Table Mountain Sandstone. (Ref 1)