Abstract:
The aquifer vulnerability of the Molototsi
(B81G) and Middle Letaba (B82D) quaternary catchments
was assessed to determine the influence of the vadose zone
on the groundwater regime. The aquifer vulnerability was
assessed by developing a new method, which evaluates the
vadose zone as a pathway for pollutants using the following
four parameters: recharge, depth to water table, soil
type (saturated vertical hydraulic conductivity) and slope
(RDSS). Recharge was estimated using the chloride mass
balance method, and the depth to the water table was
measured in the field using dipmeter. The seepage behaviour
(soil type) was determined as hydraulic conductivity
from in situ infiltration and percolation testing (SABS
0252-2:1993 and double ring infiltrometer). The slopes
were determined with the digital elevation method using
ArcGIS software. The four parameters were overlaid using
weighted sum, weighted overlay and raster calculator to
produce the vulnerability map. Different weightings were
attributed in the methods and the best selected. The results
obtained indicated high vulnerability on the lower and
upper parts of both catchments. The benefits of the method described are (a) the easy quantification of the parameters
through fairly simple methods and (b) the exclusion of
arbitrary index values.
