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ground beneath gum and wattle trees for example (although pine trees do build up a good
ground cover of pine needles with time).
11.6.3 Hydrogeological characteristics of geological formations and methods of
groundwater extraction
(al Primary aquifers
(i) Alluvial and estuarine sediments (Quatemaryl
• Aquifer characteristics
Sandy sediments of alluvial and estuarine origin of Quaternary age can be an important·
source of groundwater, especially if the rivers concerned drain an area of mainly granitic
geology which yields a coarse (Umgeni type) sand - as is evident in many of the coast and
coastal hinterland rivers of NatallKwaZulu. Whereas the depth of sediment above the
underlying bedrock is limited to a maximum of about 6 - 8 m in river courses inland of the
"estuaries" (this depth of sediment occurring in basins of softer rock between shallower
buried bars of hard rockl, in the estuaries themselves, the depth of sediment can be as
much as 50 m in the case of major rivers. As the shoreline is approached however, the
incidence of impermeable silt and clay horizons generally increases in the profile, to the
extent that no exploitable aquifers may be present in these localities, the quality of the
groundwater also deteriorating progressively as the number of clayey horizons increases,
and the shoreline is approached.
• Shallow well points
Groundwater contained in the shallow sandy aquifers beneath and adjoining river beds can
be exploited by well point systems. The maximum depth to which these can operate
satisfactorily is about 6 m, due to the water being extracted by means of vacuum pumps.
Well points can be installed by jetting or hammering. Individual well points are normally
spaced about 5 - 6 m apart. Yields from 50 mm diameter individual well points are usually
in the range 1 - 2 m 3 h- 1 in suitably coarse sandy alluvium. Water quality is generally