THUKELA RIVER

THUKELA RIVER: Topography, geology and soils

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Map of the THUKELA River

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TOPOGRAPHY

The Thukela River and some of its main tributaries rise in the west of the catchment in the high lying Drakensberg Mountain Range. The headwaters of the main stem Thukela River originates at an elevation of some 3 000 m.a.s.l. The river then winds its way through gently rolling hills before entering steep sided gorges below Colenso. This rugged topography continues down to the river mouth only broken occasionally by flatter, more densely populated floodplains. The Little Thukela, Bushmans, Sundays and Mooi Rivers meander down through the mountains through relatively undulating terrain before joining the Thukela River. The source of the Buffalo River is also reasonably high lying but flows through more rugged topography and gorges in the lower half of its trajectory. (Ref.1)

GEOLOGY

The upper and middle Thukela River flows eastwards through a succession of sedimentary strata of the Karoo Supergroup, ranging from the younger rocks of the Triassic System (situated just below the Drakensburg volcanics) to the base of the Karoo succession in the Tugela Ferry area. (Ref.1)

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 and Ecca series. Thick grey to brown silty sand is typical of the debris presently being discharged by the Thukela into its estuary. (Ref 2)

90% of the Thukela catchment is underlain, from the high altitude west to the lower altitude east, by Triassic basalt over Permian / Carboniferous sandstones and shales with coal rich seams. Towards the east, older Devonian sandstones overlay Archaean basement complex granites and gneisses, with the sequence largely mirror-imaged near the coast as a result of monoclinal uplifting. (Ref 3)

SOILS

The geomorphology of the Thukela River is strongly associated with the underlying geology and the erosion resistance of the various formations on a regional scale is reflected by these characteristics. Parts of the catchment are quite densely populated. The arid and often erosive landscape, coupled with overgrazing and extreme pressure on natural resources has led to the loss of vegetative cover, erosion, and sedimentation. Ref.1.

The average annual sediment load at the Thukela Mouth has been estimated at 5.5 million tons (Midgley et al, 1994). (Ref.1.)

Major Land Cover:

degraded grassland; degraded thicket and bushveld
unimproved natural grassland (Ref 3)

Major "Natural" Land Cover (Note: veld=range)

Southern tall grassland (35%)
Natal sour sandveld (15%)
Valley bushveld (20%)
Highland sourveld and D�hne sourveld (18%)
Others (12%) (Ref 3)

References

Ref 1: Department of Water Affairs and Forestry, South Africa. 2004. Internal Strategic Perspective: Thukela Water Management Area : Prepared by Tlou & Matji (Pty) Ltd, WRP (Pty) Ltd, and DMM cc on behalf of the Directorate: National Water Resource Planning (East). DWAF Report No. P WMA 07/000/00/0304.

Ref 2: The Estuaries of Natal by George Begg

Midgley, DC, Pitman, WV and Middleton, BJ (1994). Surface Water Resources of South Africa 1990. Volume VI. Drainage Regions U,V,W,X - Eastern Escarpment� Appendices and Book of Maps. WRC Report Number 298/6.1/94.

Ref 3: Professor R.E. Schulze University of Natal , Pietermaritzburg, South Africa School of Bioresources Engineering and Environmental Hydrology (BEEH)

Ref 4: Schulze, R.E., Dlamini, D.J.M. and Horan, M.J.C. 2005. The Thukela Catchment : Physical and Socio-Economic Background . In: Schulze, R.E. (Ed) Climate Change and Water Resources in Southern Africa: Studies on Scenarios, Impacts, Vulnerabilities and Adaptation. Water Research Commission, Pretoria, RSA, WRC Report 1430/1/05. Chapter 10, 191 - 209.

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