The Kalahari is situated in the semi-arid center of southern Africa and can
be characterized as a savannah with a sandy subsurface, deep groundwater t
ables and annual rainfall ranging from 250 mm in the southwest to 550 mm in
the northeast. A high infiltration rate and high retention storage during
the wet season and subsequent high transpiration by the dense vegetation du
ring the dry season, make that very little water passes the root zone and c
ontributes to aquifer recharge. A lively debate has continued for almost a
century on the question whether the Kalahari aquifers are being replenished
at all under present climatic conditions. The present paper reports on res
ults of an extensive recharge research project at the eastern fringe of the
Kalahari, which is the most favorable part for groundwater replenishment.
Additional observations were made in the central Kalahari. Environmental tr
acer studies and groundwater flow modeling indicate that present-day rechar
ge is in the order of 5 mm yr(-1) at the eastern fringe of the Kalahari whe
re annual rainfall exceeds 400 mm. Figures in the order of 1 mm were obtain
ed from the central Kalahari with lower precipitation. A dry valley system
refers to more humid paleo-climatic conditions with a higher groundwater re
charge. A tentative reconstruction of the groundwater depletion history sug
gests a time lapse of several thousands of years since the end of the last
wet period. (C) 2000 Elsevier Science B.V. All rights reserved.