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Basin Landscape

Basin Topography

The geography of Limpopo River basin can be considered as two main physiographic regions - the upper, western basin characterised by the western plateau topography, bordered in the south with a moderately mountainous region; and the lower, eastern floodplain, or coastal plain.

As can be seen from the topography map below, the majority of the land forms in the basin are characterised as undulating plain, interspersed in the west by medium and low gradient mountains and hills (CGIAR 2003). The land forms of the eastern basin are considerably more homogenous, with the majority being coastal plain and valley floor (CGIAR 2003).

The higher elevation areas of the river basin are the Waterberg, Strydpoort Mountains and the Drakensberg range, with elevations reaching over 2 000 m above sea level in the far south of the river basin, east of Johanneburg and Pretoria. As the Limpopo River traverses the last 175 km of its course across the eastern coastal plains in Mozambique, the elevation varies very little, with the majority below 7 m above sea level.

Landforms

The dominant landforms of the basin are plateaus, interspersed and interrupted by medium gradient mountains, deeply incised valleys and low-gradient hills (FAO 2004). The geomorphology of the basin, has a distinct influence on the regional climate of SADC, with the distribution of high elevation land has a significant effect on precipitation patterns in the Limpopo River basin. This in turn impacts the landscape, as the distribution and intensity of rainfall impacts geomorphology, with the resulting surface, sub-surface and stream flow all affecting erosional processes.

These landscape elements are shown in the map below using data from the FAO (1993). The dominance of the plain and plateau topography is clearly illustrated.

Landform Descriptions of the Limpopo River Basin

Plains

The plains (gently undulating to undulating, 0-600 m) are the lowveld of South Africa and Zimbabwe, and the coastal plains of Mozambique. The higher western part (300-600 m) forms the piedmont zone of the escarpment, consisting of eroded foot slopes, developed in mainly granite. Dolerite intrusions occur throughout the lowveld.

The South African and Mozambican plains are separated by the Lebombo Ridge, which is a cuesta, or a tilted plateau with a steep escarpment bordering the lowveld and a gradual dipslope of about 5 percent descending east into the coastal plains of Mozambique. This ridge, consisting of rhyolite, is more prominently developed towards the south, outside the Limpopo River Basin.

West of the Lebombo Ridge, north-south zones can be distinguished by rock types. In the Kruger National Park, there is a distinct zone of Karoo basalts, followed by Karoo sediments of the Ecca series (shales and sandstones) lying west.

The southeast lowveld of Zimbabwe is a broad pediplain with elevations of generally less than 600 m and an almost flat to gently undulating topography. The transition to the middleveld is gradual. The pediplain of the southeast lowveld is developed in paragneiss of the Limpopo and Zambezi mobile belts, Karoo volcanics, and for a small part in Karoo sedimentary rocks.

In Mozambique, landforms in most of the interior basin east of the Limpopo River comprise flat to gently undulating plains, valleys, minor valleys and plateaus, not exceeding 5-8° in slope and 100 m in elevation. This unit coincides with the dominant soil characteristics belonging to the Mananga group of soils. Coastal dune and plain formations, extending inland from the coast to border the Changane River, dominate the landscape in the lower Limpopo River Basin. Extensive areas of floodplains exist along the Limpopo and Changane Rivers, with hills and minor scarps enclosing the middle-upper reaches of the Limpopo River as well as the Elephants River, the latter above 1 200 m.

Plateau

The plateau (flat to undulating, 600-1 500 m above sea level) includes the highveld area of Botswana, Zimbabwe and South Africa. Although the Limpopo drainage system has eroded deeply into the overall plateau, it has not formed a distinct valley and thus a separate landform unit. Slopes towards the rivers are generally gradual. The plateau includes subordinate occurrence of groups of hills and ridges, which can be distinguished at more detailed scales.

In Botswana, the Limpopo River Basin starts within the transition boundary with the Kalahari sands. At Serowe, a distinct escarpment is formed in Karoo sandstone. The majority of the plateau is flat to gently undulating, in places undulating to rolling with kopjes. The main rock type is granite or granitic gneiss. Sandstones occur south of Mahalapye, and basalt dominates the eastern tip of Botswana, with some subordinate occurrences at Serowe.

Several groups of relatively small hills occur in the southern and central parts of the Botswana hardveld, in particular near Gaborone and Palapye, often with flat tops at levels of about 1 200 m above sea level, corresponding with the African plantation surface. These hills of medium relief (200-400 m above the base) consist mostly of sedimentary rock, but are also formed of dolerite (Shoshong) and other rock. The hills, e.g. the granite hills near Mahalapye, are often associated with pediments.

The plateau developed on the Basement Complex continues on the eastern side of the Limpopo River, in South Africa, also with a flat to gently undulating topography. The occurrence of Karoo sediments (sandstones and shales), including coal deposits near Middelburg and Witbank, characterizes a large area of the southern highveld.

North of the Limpopo River, the plateau includes parts of the southern highveld region of Zimbabwe (above 1 200 m above sea level, with Plumtree-Bulawayo as the main catchment) and the adjacent southeast middleveld region (600-1 200 m, near Gwanda and surroundings). Tributaries of the Shashe and Limpopo Rivers, which run in a north-south direction, dissect the middleveld. Rocks of the Basement Complex with greenstone belts dominate the geology.

Hills

In South Africa, quite large hilly areas (rolling, 400-600 m above sea level) and ridges occur in the southwest half of Limpopo Province. These hills of the Bushveld Complex include the Waterberg Hills - which could also be described as a plateau - and also groups of hills towards the southern edge of the catchment (Pilanesberg and Magaliesberg). The lithology of these hills differs from the granite of the basement, and includes quartzite and resistant rock types.

Escarpments

The escarpment zone is a complex landscape consisting of steep hills and mountains (600-1 500 m), forming the transition from the highveld or Transvaal Plateau to the coastal plains of the lowveld. The escarpment at the southeast divide of the Limpopo River Basin forms the watershed with the Komati River. Some parts rise to more than 1 500 m above sea level (medium relief class).

The Drakensberg Mountains form the highest part of the escarpment, rising above 2 300 m. Low, east-west mountain ridges (e.g. Soutpansberg and Strydpoortberg) arise above the plateau and link up with the escarpment. The escarpment is characterized by a complex of steep slopes between low and high levels, dissected plateaus and plateau remnants, with associated hills, valleys and basins.

Source: FAO 2004