VAAL RIVER: Topography, geology and soils

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Map of the VAAL River

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TOPOGRAPHY
The Vaal river slopes gently from about 1 800 m in the east at its origin  to 1 450 m in the vicinity of the Vaal Barrage at Vereeninging. (Ref 1.) The area between the confluence of the Vaal and the Rietspruit Rivers and the Bloemhof Dam is relatively flat with a maximum elevation of about 2 200 m in the hilly upper reaches of the Vals River and a minimum elevation of about 1 250 m in the vicinity of Bloemhof Dam. Pans and other enclosed drainage basins are features of the western parts. (Ref.2.). The area between the Bloemhof Dam and the confluence of the Vaal and the Orange Rivers has no distinct topographic features with most of the terrain being relatively flat. (Ref.3.)
    GEOLOGY                                    
Upper Vaal Area (Upstream of the Vaal Barrage at Vereeninging): The Karoo system (underlain by fine sedimentary rocks) covers about 80 % of the catchment. North of the Vaal River, west of longitude 28° E, igneous and metamorphic rocks predominate but there are extensive dolomitic exposures in the central areas which are mainly in the catchment of the Mooi River tributary. The predominant minerals are gold, uranium, base metals, semi-precious stones and industrial minerals. Gold mining, is of particular economic importance. Also of importance are uranium and coal mining. The mining of these minerals have implications in terms of water quality impacts.(Ref 1.)
Middel Vaal Area (between Rietspruit River and Bloemhof Dam): The geology is varied with a large dolomitic intrusion occurring in the Orkney area. Diamonds are found in the north east of the area, with rich gold ore in the vicinity of Klerksdorp and Welkom. The area south of the Vaal River is underlain by fine sedimentary rocks of the Karoo system and to the north of the Vaal River igneous and metamorphic rocks predominate, with extensive dolomitic exposures in the north and east of Klerksdorp. (Ref.2.)
Lower Vaal Area (between the Bloemhof Dam and the Orange River):  The northern and western part, which corresponds  with the catchment of the Molopo River, is mainly underlain by sedimentary formations and covered by Kalahari sands. A large portion of the central and north-east corner of area is underlain by the Transvaal Supergroup consisting of the dolomite, chert and subordinate limestone. Rich diamond bearing intrusions occur near Kimberly with alluvial diamonds found in the vicinity of Bloemhof. Iron ore and a variety of other minerals are found in the central to south-western parts of the area. (Ref. 3.)
    SOILS                                    
Upper Vaal Area (Upstream of the Vaal Barrage at Vereeninging): Soil depths are generally moderate to deep upstream of the Vaal Barrage at Vereeninging.. There are three main soil types that predominate in this area:(Ref 1.)
Sandy Loam in upper reaches of the Vaal and Wilge catchments and to north of the Vaal River along its central reaches. Ref 1.
Clay Loam in the Klip (Gauteng) and Suikerbosrand catchments and to the south of the Vaal River along its central reaches. Ref 1.
Clay Soil in the middle and lower catchments of the Wilge and Vaal catchments. Ref 1
Middel Vaal Area (between Rietspruit River and Bloemhof Dam): Soil depths are generally moderate to deep with flat to undulating relief over the entire area. There are three main soil types that predominate the area:
Sandy Loam : Most of the area consists of this soil type.
Clay Loam: This soil type extends from the sandy loam area further eastwards into the headwaters of the Sand, Vet, Elandspruit and Renoster Rivers.
Clay Soil: A relatively small area at the confluence of the Sand and Vet Rivers.
  References                                      

Ref 1. Department of Water Affairs and Forestry, South Africa. 2004. Upper Vaal Water Management Area: Internal Strategic Perspective. Prepared by PDNA, WRP Consulting Engineers (Pty) Ltd, WMB and Kwezi-V3 on behalf of the Directorate: National Water Resource Planning. DWAF Report No P WMA 08/000/00/0304.

Ref 2. Department of Water Affairs and Forestry, South Africa, Middle Vaal Water Management Area: Internal Strategic Perspective, 2004. Prepared by PDNA, WRP Consulting Engineers (Pty) Ltd, WMB and Kwezi-V3 on behalf of the Directorate: Water Resource Planning. DWAF Report No P WMA 09/000/00/0304)

Ref 3. Department of Water Affairs and Forestry, South Africa. 2004. Lower Vaal Water Management Area: Internal Strategic Perspective. Prepared by PDNA, WRP Consulting Engineers (Pty) Ltd, WMB and Kwezi-V3 on behalf of the Directorate: National Water Resource Planning. DWAF Report No P WMA 10/000/00/0304).

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