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

5.2.5 Water quality data
No specific water quality data for this sub-catchment could be obtained in time for this report. In view of the very
limited mining activity, this deficiency is not considered to be important.
5.2.6 Implications for water quality and quantity management
The available evidence suggests that the limited mining and quarrying activities carried out in this catchment
would be likely to have very minor, localized impacts on the water resources of the sub-catchment. These
impacts would be likely to consist of very slight instances of acid mine drainage and an increase in suspended
sediment loads in nearby streams and rivers as soil is eroded from exposed areas. There is also a likelihood
that seepage of high salinity power station cooling water and seepage from coal ash dumps at the two thermal
power stations.
5.3 The Little Olifants - Riet sub-catchment
5.3.1 General description
5.3.1.1 Hydrology
The hydrological features of this sub-catchment are very similar to those of its eastern neighbour, the Wilge subcatchment.
The Little Olifants - Riet sub-catchment consists of the area drained by the upper reaches of the
Olifants, Little Olifants and Riet rivers and their tributary streams, down to the point where the Olifants River
joins the Wilge River at the Loskop Dam (Figure 4.2). The Olifants, Little Olifants and Riet rivers drain a
relatively small area that includes the coal-mining towns of Witbank and Middelburg located to the east of
Pretoria. The sub-catchment receives additional water via three inter-basin transfer schemes from the Vaal,
Usutu and Komati systems, whilst relatively large discharges of treated domestic and industrial effluent from
Witbank and Middelburg supplement flows in the Olifants and Little Olifants rivers. All rivers and streams in this
sub-catchment are perennial.
The sub-catchment contains four water supply dams, one of which (Loskop Dam) also supplies water for the
extensive irrigation agriculture areas downstream of this sub-catchment. The other dams all supply domestic
and industrial water to the towns of Witbank and Middelburg as well as the numerous collieries and smaller
settlements in the sub-catchment. In addition, the sub-catchment has numerous small farm dams that trap
runoff in seasonal channels and supply this water for limited livestock watering.
The sub-catchment also contains an enormous number of small wetlands located every stream and river
(Marneweck et al., 2001). These are formed at the uphill side of protruding dolerite formations (typically dykes
and sills) that dip gently to the south. These dolerite formations act as impermeable barriers and water collects
on their uphill sides, saturating the soils. The downstream end of each wetland is usually marked by a dolerite
exposure where the water reaches the ground surface and flows over the dolerite barrier. This system of inter-
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