ESTUARIES IN SOUTH AFRICA

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SWARTLINTJIES RIVER ESTUARY: Catchment Characteristics

	Main Rivers and tributaries
	The catchment area is given as 1687 km² by Heydorn and Tinley (1980), whereas Memoranda from Agricultural Technical Services (1975) record the catchment as being 104 000ha in extent. The river drains the edge of the Namaqua-bushmanland escarpment with a network of smaller unnamed tributaries on the coastal plain. (Ref1)
	The Swartlintjies is approximately 30 km long from themouth up to where it splits into a number of unnamed tributaries. The total length of the system is 65 km. (Ref1)
	Dams

	River run-off
	At the timeof the ECRU survey on 16 October 1980 the riverbed was dry, except for a few standing pools approximately 10km from the mouth. Two small excavated treches and a waterhole on the edge of the dry riverbed cpmtaomed water at approximately 0,75m below the surrounding ground level.
	Two large excavated trenches just north of the mouth contained water which is pumped up to the Koingnaas mine. Seawater and subterranean water from the riverbed seeps into these water supply trenches at their southern end. After rains in the catchment water flowed in the upper reaches of the river during Aug/Sept of 1980 but no water reached the mouth ( Mr C, Sweet pers.comm.).
	Geomorphology

	Geology
	A detailed description of the geological formations found on the Koingnaas group of farms which includes the Swartlintjies Estuary is given in a guidebook prepared for a visit by the Geological Society of South Africa to Namaqualand in November 1979. According to the guidebook the sediments in the area are known localy as the Koingnaas Complex. The Basement rock falls within the Namaqualand-Natal belt of metamorphism and granitization and this is overlain by a number of sedimentary sequences.
	This entire geological sequence is overlain by scrub covered, loose, aeolian sand and several quartzitic dune-fields. (Ref 1)
	There are 3 distinct bands of surface soil formations. A triangle of unvegetated barchanoid dunes lies to the north of the rivermouth adjacent to the coast, with reddish sand present in the dune slacks. This is followed by a band of vegetated white dunes approximately 400m wide, followed by vegetated red sands with darker termitaria "heuweltjies" extending inland. (Ref 1)