OVERVIEW OF THE IMPACT OF MINING ON THE ... - IIED pubs

In the following portions of this sections of the report that contain descriptions of the mining and mineral
processing activities in each sub-catchment, it is important to refer to Figures 4.2 and 4.3, as well as Figure 3.2
for the positions of the different sub-catchments within the Limpopo basin.
4.2 The Ngotwane-Bonwapitse sub-catchment
4.2.1 General description
4.2.1.1 Hydrology
The Ngotwane River and its major tributary the Bonwapitse River rise in a range of low sandstone hills at the
edge of the Kalahari Desert to the southwest of the Botswana capital, Gaborone, and north of Gaborone,
respectively. The Ngotwane River flows in a north-easterly direction to join the Limpopo River some 50
kilometres downstream of the confluence of the Marico and Crocodile rivers, near Steenbokpan. The
Bonwapitse River also flows in a north-easterly direction, joining the Limpopo River some 60 kilometres
downstream of the Ngotwane-Limpopo confluence.
The Ngotwane River is dammed near Gaborone (Gaborone Dam) and provides the main source of domestic
and industrial water for the city. Several small farm dams and numerous boreholes provide water for smallscale
irrigation and stock watering in several parts of this sub-catchment.
4.2.1.2 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.
4.2.1.3 Pedology, agriculture and land use
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.
The sub-catchment receives low and unreliable rainfalls (under 500 mm per year) with high evaporation rates.
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.
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