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groundwater consumption in Natal/KwaZulu are provided in the chapter on the surface
water resources of Natal/KwaZulu, elsewhere in this publication.
Over 90% of South Africa's groundwater occurs in limited volumes in numerous small
secondary aquifers, specifically in the near-surface fractured and weathered part of hard
rock formations of igneous, metamorphic and sedimentary origin*. Secondary aquifers
are used mainly on farms for domestic needs, for stock watering and for small scale
irrigation. Villages and small to medium sized towns can also be supplied from suitable
secondary aquifers. Larger volumes of groundwater are only found in a few geological
formations with a relatively small areal distribution. These sources are the extensively
leached (karstified) dolomitic strata of the southern and western Transvaal as well as the
northern Cape; the (primary) geologically young coastal sand deposits, and alluvium along
some rivers. The popular misconceptionthat all groundwater exists as "underground rivers
and streams" is only true in a few dolomitic and limestone areas.
Yields from boreholes in South Africa can be classified according to their potential use.
Boreholes with a low yield « 1 t s-1) should be used for gardening as well as for domestic
and stock purposes. Medium yield boreholes (1 - 5 t s-1) have a similar use, while high
yield boreholes (5 - 20 t s-1) can supply small villages and towns. Very high yield
boreholes (> 20 t s-1) are suitable for large scale irrigation and urban requirements. It
should be borne in mind that in many parts of South Africa, typical borehole yields average
less than 2 t s-1 (Vegter, 1984).
The exploitation potential of groundwater is determined by the volume of water held
underground, the recharge rate, and losses through seepage to springs, wetlands, streams,
lakes, "estuaries", and the sea. Also important are evapotranspiration losses.
Groundwater use is likewise constrained by practicality and economics. In secondary
aquifers, low borehole yields effectively prevent exploitation ofthe resource for bulk water
supplies. Umited demand and associated costs may also not justify the maximum
exploitation of groundwater. In certain areas of the Karoo for example, groundwater
*
A useful glossary of South African groW'ldwater tenns can be foW'ld in the following: Parsons, R.,
1995. A South African aquifer system management classification, WRC Report No. KV 77/95, Water
Research Commission, Pretoria, 20 p. + app. Any comprehensive textbook on groundwater may
likewise be consulted. See also: Pfannkuch, H-Q., 1990. 8sevier's Dictionary of Environmental
Hydrogeology: in Enolish. French and Gennan, revised edition, 8sevier, Amsterdam, 332 p.