ESTUARIES IN SOUTH AFRICA

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State of Rivers Reports - Rivers of the Gouritz Water Management Areas 2007

Main Page	General Information	Land and Estuary Uses	Ecology	Water Quality
Threats	Hydrodynamics and mouth dynamics	Physical Features	Climate	References
KNYSNA ESTUARY: Catchment Characteristics

	Main Rivers and tributaries
	The length of the river is approximately 60 km. The catchment area is approximately 525 km². (Ref. 1). The river flows into the Knysna estuary (often refers to as the Knysna Lagoon).
	Tributaries of the Knysna River are the Dwars, Gouna, Kruis, Lawnwood, Lelievlei, Oubos, Palmiet, Rooiels, Steenbras, Steenbras, Swartkops and Witels Rivers (Ref 1)
	Dams

	River run-off
	The river flow is usually not strong (Day et al.,1952). The only hydrological gauging stations in the catchment area, is a continuous recorder at a causeway on the Gouna river in Concordia Plantation and a gauging weir on the Knysna River at Laer Steepbos. (Ref 1)
	Geomorphology

	Geology
	The catchment of the Knysna River lies within the Cape Fold Belt with its long faults and folds that strike east-west. These old features provided a framework for the Mesozoic and Cenozoic fabric. Knysna is a true drowned valley, more or less silted up (Krige,1927). The oldest rocks in the area (of late Precambrian age) are found south of the Outeniqua Mountains to the west of Knysna. They consist mainly of contorted bands of schist, phyllites and feldspathic quartzites of the Kaaimans Formation. The adjoin outcrops of intrusive gneissic granite further to the west, but these old rocks are not in the Knysna River catchment. Most of the catchment lies in rocks of the Table Mountain Group, including the Peninsula, Cedarberg, Tchando and Kouga Formations. These rocks are supermature quartz sandstones which constitute the mountain ranges of the Cape Fold Belt and are believed to be mainly of marine origin. Geologists familiar with this area stress that this heavily faulted area is potentially seismically active and point out that this may be important when considering building developments on steep unstable slopes. The Baviaanskloof Formation, the youngest of the Table Mountain Group and the overlying Gydo Formation of the Bokkeveld Group, lies beyond the Knysna catchment. (Ref 1)
	Deposits that are believed to be Cretaceous or Early Tertiary age appear at Knysna (Miller, 1963;DuToit,1966;Butzer and Helgren,1972;Toerien,1979). The Enon pebble conglomerates represent torrential deposits in an arid climate under strongly oxidising conditions which give these deposits their characteristic reddish colour. These deposits are part of the Uitenhage Group with the terrestrial Enon conglomerates succeeded upwards by estuarine deposits. The conglomerates consist predominantly of rounded Table Mountain Group quartzite clasts (fragments of pre-existing rock) set in a sandy matrix which laterally, interfinger with finer sandstones and mudstones. A sequence of estuarine deposits occur in the Knysna Formation north of the town and contain lignites up to 1,5m thick (Du Toit,1966;Thiergart et al.,1963). Plant fossils include Podocarpus and Widdringtonia and pollens indicate Knysna forest tree species but work by Thiergart et al. (1963) on Early Tertiary pollens reveals that the flora differed from that of the modern forest and include a palm. (Ref 1)