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(iii) Holocene sands lQuaternary)
185
Along the eastern margin of the Zululand Coastal Plain lmainly in Maputaland), but also
extending further south into the Richards Bay area, shallow groundwater perched in the
base of the young Holocene age cover sands (on the impermeable surface of the
underlying more clayey Port Durnford Formation)", is exploited using shallow wells up
to 4 - 6 m deep. This is only possible where the thickness of the cover sands does not
exceed such a depth, and where the mean annual rainfall is in excess of approximately
800 mm.'
The shallow wells generally consist of simple open pits, but deeper wells, as drilled by the
KwaZulu Department of Agriculture and Forestry, are lined with concrete rings and are
covered with a concrete slab. On some of these improved wells. windmills or solar pumps
have been installed. for example. where the well is the water supply for a clinic or
transport depot. Usually however, the water is hand-bailed from the base of the well as
a source of domestic water. Although water quality is very good (with a TD5 content
often less than about 600 mg r 1 1. the yields of these wells are generally not large. due
to the relatively low transmissivity of the fine sand comprising the aquifer. Yields from
such wells seldom exceed about 1 m 3 h- t . As shown by the drilling of numerous
unsuccessful deep boreholes into the underlying Quaternary Port Durnford Formation.
which extends to a depth of about 30 m, and below into the deeper underlying Cretaceous
5t Lucia Formation, little. if any possibility exists of obtaining larger groundwater supplies
from greater depths. The siltstones of the gently seaward dipping 5t Lucia Formation and
older Cretaceous formations which underlie the Zululand Coastal Plain to a very
considerable depth - the thickness of which increases in a seaward direction to some
2 500 m at the coastline - are extremely poor aquifers. The limited groundwater which
may be present in these rocks of marine origin is usually highly saline.
." The perching of the water table on the impermeable lower member of the Port Dumford Formation
is exploited in the extensive dredge pond mining of heavy minerals present in the overlying cover
sands. as undertaken in the Richards Bay area.