GREATKEI RIVER: Topography, geology and soils

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Map of the GREATKEI River

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TOPOGRAPHY
    GEOLOGY                                    
The plateau area is predominantly covered by grassveld and savanna with varying degrees of invasion by Acacia Karoo (thornveld). Valley thicket is located in the lower reaches of the Black Kei River valley.
The area is underlain by horizontal to very gently dipping rocks of the Karoo Supergroup (shale, mudstones and sandstones) with the Molteno formation in the uplands of the Tsomo catchment and the Tarkastad formation over the remaining area. The area is characterised by dolerite intrusions often in the form of ring structures. The Thomas River and town of Cathcart are located within one such ring structure. (Ref 1)
The plateau area is predominantly covered by grassveld with large areas of valley thicket in the Great Kei valley and its small steep sided tributaries. (Ref 1)

The Adelaide subgroup comprises mostly mudstones alternating with lithofeldspathic sandstones. The Tarkastad subgroup is characterized by a greater proportion of sandstone and red coloured mudstone. The Molteno formation contains yellow grey sandstones alternating with olive mudstones and grey shale. The Elliot formation which overlies the Molteno formation comprises an upward fining cycle of sandstone, siltstone and mudstone. 

There are extensive intrusive hypabyssal dolerite sills and dykes throughout the area with characteristic ring structure formations in the Upper Kei catchment around Queenstown. The Amatola mountain range forms the southern boundary of one of these ring structures. (Ref 1)

    SOILS                                    
Soils are generally moderate to deep clayey loams in the Thomas River catchment with very shallow and rocky soils mostly not suitable for crop production in the Tsomo River catchment. Alluvial soils are found in the river valleys. (Ref 1)
Soils are poorly developed, being shallow and rocky and mostly not suitable for crop production. In general shallow residual soils and rock occur on hilltops with talus on the slopes and slightly deeper residual soils in the valleys. (Ref 1)
  References                                      

Ref 1:  Department of Water Affairs and Forestry, South Africa. 2004. Mzimvubu to Keiskamma Water Management Area : Amatole – Kei Internal Strategic Perspective. Prepared by FST Consulting Engineers (Pty) Ltd in association with Tlou & Matji and Umvoto Africa, on behalf of the Directorate : National Water Resource Planning. DWAF Report No. P WMA 12/000/00/0404.
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