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

5.6.6 Implications for water quality and quantity management
The available evidence suggests that the only likely source of any impact on local water resources and water
quality would be the two small gold mines located near the town of Pilgrims Rest (Table 5.12). These impacts
would most likely be localized and consist almost entirely of minor increases in suspended sediment
concentrations and, possibly, the risk of small cyanide spills from the extractive workings. It is also likely that
the many (> 100) small, abandoned gold mines and surface workings around Pilgrims Rest will be subject to
acid mine drainage linked to the oxidation of pyrite in the gangue rock. A few small associations of arsenopyrite
in the gangue rock suggest that arsenic may also cause minor, localized problem in a few streams.
5.7 The Selati sub-catchment
5.7.1 General description
5.7.1.1 Hydrology
The Selati River rises on the eastern slopes of the Wolkberg Mountains, which form part of the Drakensberg
Mountain chain. From its source in this high rainfall zone, the river flows eastward for approximately 140
kilometres before joining the Olifants River some 10 kilometres to the east of the town of Phalaborwa. The
Selati River has two main tributaries in its upper reaches; these are the Ngwabitsi and Mulati rivers.
The upper reaches of the Selati sub-catchment consist of steep-sided valleys with sharply defined cliff faces on
the eastern side of the escarpment. The local relief changes dramatically as the escarpment drops sharply on
its eastern flank to the flat or undulating terrain of the dry Lowveld region. Here, the topography is characterized
by gently sloping valleys and isolated outcrops of granitic rocks.
Immediately downstream of the Gravelotte road bridge, the Selati River is partially impounded by a series of 10
small weirs over a distance of some 20 kilometres. These weirs mark the points where irrigation water is
abstracted for large-scale commercial irrigation farms.
In its upper reaches, the Selati River is perennial. However, the combination of little or no inflows from seasonal
tributary streams in its middle and lower reaches, coupled with large-scale water abstractions in the middle
reaches, has resulted in the Selati River being a seasonal river over most of its lower reaches. At the town of
Phalaborwa, discharges of treated domestic effluent and seepage from large-scale tailings dams provide a
source of “perennial” flows for the final few kilometres before it joins the Olifants River. In effect, the final few
kilometres of the Selati River only contain effluent during the dry winter months, though this becomes “diluted”
when normal summer flows resume.
5.7.1.2 Geology
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