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

continues to flow in the deeper alluvial deposits. The western and central parts of the basin that receive the
lowest rainfalls have mainly seasonal or episodic rivers that have no surface flow during the dry winter months.
Recent studies on the Limpopo River (Boroto & Görgens, 1999) have focussed on the development of an
accurate hydrological modelling system that can incorporate the flow contributions of the four basin states. The
available information on flows in the Limpopo River is relatively poor and there are significant differences
between the flows gauged by different countries. An important hydrological characteristic of the Limpopo River
is the very large transmission losses (> 40%) that occur along its length. Whilst a part of the water loss can be
accounted for by the large volumes of water transpired by riparian vegetation, there is still uncertainty as to
where the remaining losses occur (Boroto & Görgens, 1999). Overall, flows decline along the length of the
Limpopo River and very little water discharges to the sea at Xai-Xai.
The demand for water throughout the Limpopo basin is both high and unevenly spread. In particular, water
demands by industry, mining and especially the formal (irrigation) agricultural sector account for over 75% of all
water used. Coupled with high evaporation losses from the numerous small dams and larger water supply
impoundments, flows in the lower reaches of the Limpopo River are usually relatively small, unless they have
been “boosted” by the arrival of a tropical cyclone (e.g. the cyclone that arrived in 2000 and flooded large
coastal areas of Mozambique).
Several small, though ecologically important, wetlands are found in the Limpopo basin (Midgley et al., 1995;
Boroto & Görgens, 1999). These wetlands occur predominantly along shallow-gradient reaches of tributary
rivers in the South African portion of the basin and the Mozambique coastal plain. The most important wetland
areas in the Limpopo basin are the Nylsvley and Mogalakwena floodplains in South Africa, and the mosaic of
wetlands on the Chagane floodplain in Mozambique.
The growing water shortage in Botswana prompted the construction of the North-South Carrier, a pipeline
system that transports water from the Motloutse River southwards to the City of Gaborone. This has also been
supplemented by an inter-basin transfer scheme where water from the Marico Dam in South Africa is
transferred over the border to Gaborone in Botswana. Further investigations are underway to determine the
feasibility of extending the pipeline northwards to draw water from the Zambezi River at Kazungula. Elsewhere
in the South African portion of the basin, numerous inter-basin transfer schemes convey water from one subcatchment
to another to meet growing demands for water. In addition, three inter-basin transfer schemes
deliver water from the Vaal system in South Africa into the headwaters of the Crocodile and Olifants rivers to
provide domestic water supplies as well as cooling water for several coal-fired thermal power stations. The
overall water supply “picture” is made somewhat uncertain by the very real possibility that global climate
changes will also have an adverse effect on water availability throughout southern Africa (Ashton, 2000).
Throughout the length of the Limpopo River and its tributaries, water quality is generally good and the water is
usually fit for most designated uses. There are water quality problems due to increasing salinity in the central
parts of the basin, making the water less suitable for irrigation purposes and for domestic use. In addition, most
cities, towns and smaller communities discharge untreated or partially treated domestic and industrial effluent
into the various rivers (e.g. the cities and towns of the northern Pretoria – Witwatersrand metropolitan complex
in South Africa). As long as there is sufficient dilution, this practice does not have long-term or large-scale
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