Read the full Annual Report in PDF format - CSIR

establishing a water resources monitoring
programme for the cradle of humankind
In brief
The Cradle of Humankind World Heritage
Site (COH WHS), in one of the world’s
most important protected karst landscapes,
is threatened by acid mine drainage
(AMD).
Perceptions of this threat have generated
widespread concern since the Cradle
houses some of the world’s most revered
fossil sites, including the famous Sterkfontein
Caves. In 2008, the Management
Authority of the COH WHS commissioned
a study to develop a water resources
monitoring programme for the area.
The challenge
The Cradle of Humankind is one of seven
World Heritage Sites in South Africa. It has
yielded some of the oldest hominin fossils
ever found, some dating back as far as 3.5
million years. The fossil record spans more
than a third of the total record of human
evolution in Africa, and there is informed
expectation that further sites and fossils will
be unearthed at this location.
In late August 2002, the Western Wits
Basin outside Krugersdorp started to
decant acid mine water. This was some
six years after the last mine to shut down
underground mine workings in this basin
stopped dewatering its operations. This
followed 120 years of mining in the
Witwatersrand goldfields.
CSIR research
Led by the CSIR, a multidisciplinary
research team investigated the surface
water and groundwater resources and
their relationship in a study area of nearly
65 000 hectares. The assessment also
included an evaluation of the vulnerability
of all fourteen fossil sites to water-related
threats such as AMD and municipal waste
water. Researchers had to understand
the interaction between surface water
and groundwater; the groundwater levels
that define hydrogeologically separated
compartments; and monitor the quality of
surface and groundwater sources.
Better understanding critical for evaluation
Based on the assessment, researchers
built a conceptual model to understand
the different pathways where AMD enters,
impacts on and leaves the system.
For the first time, we now understand the
cave morphology associated with each
fossil site. This means that a cave system
is classified in relation to its setting in the
landscape. For example, a ‘near-surface’
setting describes a shallow cave system
that is mainly exposed on surface, whereas
an ‘underground’ setting describes a cave
system that also extends underground,
sometimes intersecting the groundwater
level. In this project, researchers redefined
earlier information regarding groundwater
compartments and sub-compartments in
the study area. This was established on the
basis of new groundwater level data and
a clearer understanding of spring localities,
since these indicate groundwater flow
directions. This means that the geographic
extent of contaminated water movement
in the groundwater environment will be
restricted to the southern part of the Cradle
of Humankind, leaving the more remote
and natural part unaffected.
It is especially the redefinition of
groundwater compartments, and the
location of the fossil sites within these
compartments, that determined the hydrovulnerability
of each fossil site.
Some findings
The study concluded that nine of the 14
fossil sites are not in any danger of being
impacted by contaminated water either
from AMD or municipal waste water. This is
mainly because the fossil sites are located
in groundwater compartments that are
unlikely to ever receive contaminated water.
CSIR geohydrologist Phil Hobbs measuring
the pH of acidic mine water decanting
from abandoned mines in the Western
Basin.
The Cradle of Humankind World Heritage
Site lies in a karst landscape that was
formed over 2300 million years ago. The
Cradle, and specifically the Sterkfontein
Caves, has yielded some of the oldest
hominin fossils ever found, some dating
back as far as 3.5 million years.
Apart from Bolt’s Cave and the Sterkfontein
Caves, all the other fossil sites lie well
above the ambient groundwater level.
Fortunately, the water quality in the
Sterkfontein Caves has been monitored for
the past six years, and its quality has not
been adversely impacted yet, despite the
cave water level having risen by some three
meters.
Among others, the study recommends
regular monitoring of both the cave water
level and cave water chemistry by tour
guides, as well as a more complete
water chemistry analysis twice a year. In
addition, routine monitoring of the cavedwelling
fauna in the Sterkfontein Caves
56