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

(Figure 4.2). The tributaries of the Shingwedzi River rise on the eastern slopes of the range of low, north to
south trending hills that mark the watershed between this sub-catchment and that of the Levuvhu subcatchment
of the Limpopo basin. All the tributaries of the Shingwedzi River are located in low rainfall areas and
therefore only have seasonal or episodic flows during the wet summer months of each year. Most of the
catchment area of the Shingwedzi River and its tributaries lies within the boundaries of the Kruger National
Park.
From the mid-1960s, flows in the Great Letaba River have declined progressively sue to rapidly increasing
water abstraction in the upper reaches. For the last twenty-five years, flows in the lower reaches of this river
have been entirely seasonal with no surface flow recorded during the dry winter months. This has posed
several problems for the Kruger National Park, as the Great Letaba River is an important source of water for
game animals. Accordingly, several small reservoirs were constructed along the lower reaches of the Great
Letaba River inside the Kruger National Park to provide assured supplies of water during the dry winter months.
There are a few small farm dams located in the headwater zones of all the tributaries of the Shingwedzi River;
these supply water for domestic consumption in several small settlements and mines. In the drier central and
eastern portions of this sub-catchment within the Kruger National Park, boreholes are used to supplement
water supplies during the dry winter months. In the eastern portion of this sub-catchment located within
Mozambique, the residents of the many small settlements located along the banks of the Shingwedzi River rely
on hand-dug wells in the river and stream beds for their water supplies.
5.9.1.2 Geology
The geological features of the Shingwedzi sub-catchment consist predominantly of large areas of granitic and
gneissic rocks of the crystalline Basement Complex underlying the western and central portions of the subcatchment,
together with the acidic and intermediate rhyolites and lavas of the Karoo Sequence that form the
northern extension to the Lebombo Mountains. Within Mozambique, extensive Quaternary deposits of semiconsolidated
sandstones and mudstones, with slightly older Tertiary deposits of the Mazamba, Jofane and
Cheringoma Formations, underlie the sub-catchment. In addition, there are a few outcrops of Grunja and Sena
post-Karoo complex rocks that consist predominantly of alkaline dolerites and shales. Recent alluvial deposits
are present along wide flood terraces on either side of the Shingwedzi River.
The granitic and gneissic rocks of the Basement Complex outcrop at various points across the central area of
the sub-catchment, forming prominent hills or koppies. These exposed weathered granites erode easily, and
accelerated rates of sediment production occur in this region, with large amounts of coarse and fine sediments
accumulating in river channels.
Small outcrops of the Giyani Greenstone Formation occur in the western and southern portions of this subcatchment,
together with outcrops of Timbavati Gabbro close to the Lebombo Mountains. Several dolerite
dykes and sills have intruded the Basement Complex granites and gneisses across the central and southern
portions of this sub-catchment. These rocks are less resistant to weathering than their granite and gneiss host
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