ESTUARIES IN SOUTH AFRICA

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HOLGAT RIVER ESTUARY: Catchment Characteristics

	Main Rivers and tributaries
	The total river length from the Stinkfontein Mountains in the catchment, to the mouth of the Holgat is approximately 80km.
	In the upper catchment: The Gaigais River, Klipneus River and Modderfontein se rivier drain in the western side of the Stinkfontein Mountains about 60km inland. (Ref 1)
	Dams

	River run-off
	The Holgat flows only very occasionally with the last flood having been about 50 years agao (AP Burger pers.comm). According to Keyser (1972) the Holgat last flowed in 1925. (Ref 1)
	Geomorphology

	Geology
	The geology of the Holgat is predominated by greywacke (a strongly cemented, fine to coarse sandstone large angular particles which are mainly rock fragments), grit (a coarse sandstone with grains of uneven size) and schist (medium-grained rock affected by regional metapmorphism causing a re-crystallization usually with a foliated, sometimes wavy texture) of the Holgat Formation, which is a part of the Gariep Trough. The Holgat Formation is exposed by the river along its course, extending from the mouth to well inland. North and south of the riverbed are superficial deposits of loose wind-blown sands. (Ref 1)
	On the shoreline adjacent to the mouth of the Holgat, the underlying rock is exposed. Rogers (1977) describes the bedrock composition as gneissic (a term applied to banded rocks formed during high grade regional metamorphism), arkose (a coarse-grained sandstone or grit containing a high percentage of fragments of feldspar, usually with a siliceous cement) and schist with the rocks on either side of the beach showing evidence of quartz intrusion in straight cracks. Finer straight cracks contain crumbling black material, possibly breccia (a rock composed of angular broken fragments mixed with finer material). (Ref 1)