NGOTWANE RIVER: Topography, geology and soils

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Map of the NGOTWANE River

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TOPOGRAPHY
The Ngotwane River is a tributary of Limpopo River. It flows into Botswana before turning and joining the Limpopo River. (Ref 2)
    GEOLOGY                                    
The rocks of the Kalahari Craton underlie this sub-catchment.  Large areas of the sub-catchment have exposures of Gaborone and Mahalapye granites, as well as rocks of the Palapye Suite and Lobatse and Kanye formations.  Karoo System rocks in the area contain economic sources of coal. (Ref 1)
The landscape is generally flat to gently rolling due to the Malmani dolomites. The dolomite is intruded by numerous dolerite dykes that have effectively sub-divided the dolomite into a series of compartments, which may or may not be hydraulically linked. (Ref 2)
    SOILS                                    

Soils in the sub-catchment can be divided into five groups:

  • Moderately shallow, coarse-grained feldspathic sands, derived from the Gaborone and Mahalapye granites;

  • Moderately shallow sandy loams, formed from gneisses; and

  • Shallow, clay soils with high sodium content in internally draining areas.  (Ref 1)
Soils are generally shallow and poor to medium quality.  Areas with high sodium content pose a salinization risk to irrigation farmers.  Soils become progressively sandier towards the northeast of the sub-catchment as rainfalls decline and evaporation rates increase. (Ref 1)
Moderate to deep clay loam soils with undulating topography occurs in the Upper Ngotwane catchments. These soils are also not very suitable for irrigation farming, also due to their low permeability. Overgrazing in some portions of the catchment results is excessive soil erosion and loss of land cover. This has an impact on groundwater recharge. Irrigation farming is generally practised along the Groot Marico and its tributaries. (Ref 2)
  References                                      

Ref 1:  MMSD southern Africa Research Topic 4: Impacts of Mining and Minerals Processing on the Biophysical Environment in Southern Africa

Ref 2:  Department of Water Affairs and Forestry, South Africa. 2004. Internal Strategic Perspective: Limpopo Water Management Area : Prepared by Goba Moahloli Keeve Steyn (Pty) Ltd, in association with Tlou & Matji (Pty) Ltd and Golder Associates (Pty) Ltd. on behalf of the Directorate: National Water Resource Planning. Report No. P WMA 01/000/00/0304.

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