MARICO RIVER: Topography, geology and soils

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Map of the MARICO River

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TOPOGRAPHY
The topography of the area is generally very flat with undulating hills in the lower reaches of the Marico River. (Ref 1)
    GEOLOGY                                    
In the Upper catchment of the Groot Marico as well as the Upper Ngotwane catchment, the landscape is generally flat to gently rolling due to the Malmani dolomites. (Ref 1)
In the upper reaches of this sub-catchment, the geological features are characterized by the presence of extensive dolomite and limestone formations.  Extensive areas of unconsolidated and semi-consolidated sedimentary rocks of the Transvaal Supergroup underlie the northern areas of the catchment.  These are intruded by wide belts of basic or mafic lavas in the south, with intrusions of basic, mafic and ultramafic rocks in the north.  Virtually the entire northern portion of the sub-catchment is underlain by wide expanses of acid and intermediate intrusive rocks, with intercalated assemblages of compact sedimentary and intrusive rocks.  The limestone and dolomite formations contain very large volumes of water that provide perennial flows to the Marico River . (Ref 2)
The Marico Water Management Area has a fairly uniform terrain with an altitude ranging from approximately 1700 m.a.s.l. on the Witwatersrand to about 900 m.a.s.l. at the confluence of the Crocodile and Limpopo rivers. The topography of the southern parts of the area varies from plains which have a moderate to low relief to more complex lowlands, hills and mountains to closed hills and mountains with relief varying from moderate to high. The central parts consist predominantly of plains with a low relief and towards the north the area is recognised by plains and lowlands with a low to moderate relief. Main topographic features of the water management area include the Witwatersrand , Magaliesberg, Waterberg and Pilanesberg. (www.csir.co.za/rhp/state_of_rivers/crocwestmarico_05/crocwestmarico_05_A3.pdf )
    SOILS                                    
Moderate to deep clay loam soils with undulating topography occurs in the Marico (with the exception of the lower Marico). 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 1)
Moderate to deep sandy loam soils in general flat terrain occur in the lower Marico. These soils are ideal for irrigation farming because they provide a good balance between the ability to convey water and ability to retain water. This is the area where most of the irrigation is taking place. (Ref 1)

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

  • Moderate to deep clayey loam soils on flat and undulating terrain overlying dolomite and limestone in the upper reaches of the catchment;

  • Moderate to deep clay loam soils over much of the middle portions of the sub-catchment, overlying the more porous unconsolidated sedimentary material;

  • Moderately shallow to moderately deep, clayey loam to clay-rich, fine-grained soils over most of the lower reaches of the sub-catchment; and

  • Coarser-grained sandy soils long river channels and flood terraces.  (Ref 2)
  References                                      

Ref 1:  Department of Water Affairs and Forestry, South Africa. 2004. Crocodile (West) and Marico Water Management Area: Internal Strategic Perspective of the Marico-Upper Molopo & Upper Ngotwane catchments. Prepared by Goba Moahloli Keeve Steyn in association with Golder and Associates and Tlou and Matji (Pty) Ltd. DWAF Report No. P WMA 03/000/00/0404

Ref 2:  "www.mining.wits.ac.za/FinalReport-Section5.doc."

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