ESTUARIES IN SOUTH AFRICA

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THUKELA ESTUARY: Catchment Characteristics

	Main Rivers and tributaries
	Thukela River
	Buffalo River
	Bloukrans River
	Bushmans River (from the soutwest)
	Klip River (from the north)
	Little Thukela River (from the southwest)
	Mooi River (from the southwest)
	Sundays River (from the north)
	Dams
	Bellpark Dam
	Craigie Burn Dam
	Driel Barrage
	Jagersrust Balancing Dam
	Kilburn
	Ntshingwayo Dam
	Woodstock Dam
	Slangdraai Dam
	Spioenkop Dam
	Wagendrift Dam
	Zaaihoek Dam
	River run-off
	1978 (Ref.1): Mean annual run-off: 5 071 x 10⁶ mł. It is said to be “a generous river yielding of 145 000 m³ per year from each square km of the catchment. The average annual flow is said to be from 184 m³/sec ⁽⁴¹⁾ to 226 m³/sec. The average winter discharge is given as 73,6 m³/sec and average summer discharge as 481 m³/sec.
	1999 (Ref.3): "Due to the high riverine runoff, the estuarine area of the Thukela is small. The surface area of the estuary during low flow periods is approximately 0.6 km ². However changes in river flow cause considerable changes in the morphometry of the estuary, and during periods of high flows the estuary extends out to sea and becomes unconfined by banks (Begg 1978). The axial length is estimated to be 800 m during low flow, with a shoreline length of approximately 2 km. The maximum width during natural flow periods is approximately 350 m with a channel width of 50 m, which increases to over 1,000 m during floods (Begg 1978)".
	Geomorphology
	Geology
	"The geology of the catchment is very varied, including Basaltic lava of the Drakensberg, Stormberg and Beaufort beds, old granites and gneisses, beds of Table Mountain Sandstone and rocks of Dwyka tillites and Ecca shales of the Karoo system." (Ref.1)
	Nature of the bottom materials
	1978 (Ref.1): “Thick grey to brown silty sand is typical of the debris presently being discharged by the Tugela into its estuary.. At the surface these sands may be covered by brown clayey sand. 6 km above the mouth, bedrock was overlain by 51,8m of alluvium".
	1978 (Ref.1): "The Tugela sandbar is generally a north extending structure, but is composed of a 700 m stable component (carrying coastal dune forest) on the floodplain and a 700 m unstable component (lacking vegetation), across the mouth. The latter is periodically destroyed by flood discharges. Consequently, the norm is for the bar to confine the estuary mouth to a 50 m channel on the northern bank. During floods the bar is swept out to sea and the mouth then becomes situated on the southern bank. Under such conditions, and offshore bar forms which directs the Tugela floodwaters into the sea in a southerly direction. With the perennial flow of the Tugela, the mouth is never closed".