Abstract:
A harmonised in-stream water quality guideline was constructed for the Upper and
Middle Vaal Water Management Areas (WMAs) using ideal catchment background
values for the sub-catchments; Vaal dam, Vaal barrage, Klip River and
Blesbokspruit/Suikerbosrant Rivers. Data for years 2003 to 2009 was interpolated to a
daily time-step for 2526 days at 21 monitoring sites covering both WMAs. Conductivity
was used as a surrogate to capture the variability in water quality. This provided an
ecological functionality model of the study area, coded for ranges 10-18, 19-45, 46-80,
80< and 81-100 mS/m.
The Upper and Middle Vaal basin is currently extremely vulnerable to changes in water
quality, uncertainty about changes which it can tolerate, and the fact that there are very
limited options for mitigating effects of poor water quality in the basin, overall. Thus a
precautionary approach is being proposed in this paper, in order to protect the
ecological functionality of the aquatic ecosystem. The proposed harmonised guideline
presents a crucial model to pre-determine the ecological functionality for any water point
in the study area, in order to provide upstream-downstream pollution trading and other
decision support processes towards sustainable basin management
