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

4.16.1 General description
4.16.1.1 Hydrology
This sub-catchment consists of the area drained by the Laphalala River and its tributary streams. This river
system flow northwards or north-westwards from the area to the west of the town of Nylstroom, joining the
Limpopo River downstream of the Mokolo River (Figure 4.2). The flow pattern in this river is very variable as
a result of the prevailing low and unpredictable rainfalls (average 450 mm) and the long stretches of the river
normally only contain surface water during the summer months. Most of their tributary streams are episodic
and only flow for short periods of time after local rainfalls in their vicinity. The Laphalala River contains several
small dams and numerous off-channel farm dams that are used to supply water for domestic and irrigation
purposes, as well as livestock watering (Boroto & Görgens, 1999).
4.16.1.2 Geology
The geological features of the Laphalala sub-catchment are relatively complex since they consist of several
different formations of widely differing ages. Most of the upper reaches of the sub-catchment are underlain by a
variety of porous consolidated and partially consolidated sedimentary strata, predominantly sandstones,
quartzites and felsites of the Waterberg and Soutpansberg Groups. These have been variously intruded by
acidic and basic granites and lavas of the Bushveld Complex, which in turn overlie the crystalline gneissic rocks
of the Basement Complex.
Further downstream, the sub-catchment is underlain by a sequence of sandstones and quartzites, followed by
carbon-rich mudstones and shales, and then basalts, of the Karoo Sequence. The sandstones are silicified and
resistant to weathering, remaining as harder protruding rock formations that stand well clear of the surrounding
undulating terrain to form local mountains or ranges of hills. The erosion-resistant rocks of the Waterberg
Group show a similar tendency, standing well clear of the surrounding countryside.
Large areas of the central parts of the sub-catchment are overlain by recent (Quaternary) deposits of
unconsolidated or poorly consolidated sandy material.
4.16.1.3 Pedology, agriculture and land use
Soils in the sub-catchment can be divided into three main groups:
• Moderate to deep sandy-clay loam soils on the sloping and undulating terrain in the upper reaches of the
sub-catchment;
• Moderately deep sandy loam soils lining long stretches of the valley bottoms in the middle reaches of the
sub-catchment; and
• Shallow to moderately deep sandy soils in flat and undulating terrain in the lower reaches of the subcatchment.
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