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of streams and rivers when they contain water. Van Wyk (1963)" from studies in the
northern drier parts of Natal/KwaZulu, found that groundwater recharge as a percentage
of mean annual rainfall varied from zero to nearly 20% - the actual amount averaging
about 10%. It follows that the recharge of groundwater and thus its general overall
availability will be higher and better in wetter parts of the province, rather than where drier
conditions prevail, all other factors being equal. To some extent, deeper and more clayey
soil cover can reduce the amount of recharge that would otherwise occur in areas of high
rainfall. However in the latter instance, there is usually less need to exploit groundwater
than in the drier areas. The amount of rainfall can also have a very marked effect on the
quality of the groundwater. Thus, saline groundwater is frequently encountered in areas
of low rainfall, this seldom being the case in high rainfall areas.
Topography has an important influence on groundwater in two ways. Firstly, steepness
of the ground slope (although the soil cover might be thin - facilitating deep percolation),
increases runoff and thus decreases potential recharge. Secondly, beneath elevated areas,
the depth to the water table is greater than in the more low-lying areas, this being
particularly marked on high ground adjacent to pronounced escarpments. As indicated
above, the thickness and nature of the soil cover can have an important influence on the
recharge situation. In general, the deeper the soil cover above the underlying weathered
and unweathered rock, the less rainfall penetrates through the soil column; and the more
clayey the soil, the more impermeable it is, with surface runoff on slopes (where
applicable) increasing accordingly.
The type of vegetation at any locality is mainly a function of the prevailing rainfall, where
conditions have not been modified by human activities, for instance, by crop cultivation
or the establishment of plantations. The amount of soil moisture utilized by vegetation in
transpiration can greatly influence the amount of rainfall which ultimately becomes
groundwater recharge by (a) its effect on the moisture content of the soil prior to rainfall,
which affects runoff (antecedent soil moisture), and (b) by its effect on runoff conditions
as a result of the cover afforded to the soil surface. Deep rooted plantations of exotic
trees can have a marked impact on groundwater recharge, by contrast with the natural
vegetation (usually grassland) which formerly prevailed - runoff also increasing on the bare
"
See Van Wyk, W.l., 1963. Ground-water studies in northem Natal, Zululand and surrounding areas,
Memoir No. 52, Geological Survey, Department of Mines, Pretoria, 135 p. and map.