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

4.13 The Marico sub-catchment
4.13.1 General description
4.13.1.1 Hydrology
This sub-catchment consists of the area drained by the Marico River, from its headwaters in the dolomitic
aquifers between the towns of Zeerust and Lichtenburg, to its confluence with the Ngotwane River to form the
Limpopo River (Figure 4.2). There are four relatively large water supply dams located in this sub-catchment,
of which the Marico Dam also supplies water to the City of Gaborone in Botswana. The main stem of the
Marico River is perennial, but most of its tributaries have seasonal or episodic flows. In addition to the larger
water supply dams, the sub-catchment also contains a large number of smaller farm dams used to trap runoff
in seasonal channels and supply this water either for livestock watering or for small-scale irrigation schemes.
Extensive areas of the lower reaches of this sub-catchment are internally draining and provide little or no runoff
to flows in the Marico River.
4.13.1.2 Geology
In the upper reaches of this sub-catchment, the geological features are characterized by the presence of
extensive dolomite and limestone formations. Extensive areas of unconsolidated and semi-consolidated
sedimentary rocks of the Transvaal Supergroup underlie the northern areas of the catchment. These are
intruded by wide belts of basic or mafic lavas in the south, with intrusions of basic, mafic and ultramafic rocks in
the north. Virtually the entire northern portion of the sub-catchment is underlain by wide expanses of acid and
intermediate intrusive rocks, with intercalated assemblages of compact sedimentary and intrusive rocks. The
limestone and dolomite formations contain very large volumes of water that provide perennial flows to the
Marico River.
4.13.1.3 Pedology, agriculture and land use
Soils in the sub-catchment can be divided into four main groups:
• Moderate to deep clayey loam soils on flat and undulating terrain overlying dolomite and limestone in the
upper reaches of the catchment;
• Moderate to deep clay loam soils over much of the middle portions of the sub-catchment, overlying the more
porous unconsolidated sedimentary material;
• Moderately shallow to moderately deep, clayey loam to clay-rich, fine-grained soils over most of the lower
reaches of the sub-catchment; and
• Coarser-grained sandy soils long river channels and flood terraces.
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