Abstract
Due to the geographical position of the Jukskei River in the built-up and densely populated landscape, it has been historically subject to many water quality problems, particularly of bacterial nature, as well as from other pollution sources. At one stage, between 1995 and 2005, this river was subject to increasing pH levels and variable concentrations of sulphates, potassium, phosphates and nitrates.
The potential for flooding and changes in water quality are expected to have a direct correlation to the changes in surface coverage of the built environment surrounding the Jukskei River. Major storm water management concerns have arisen in urban areas as a result of increased severity and frequency of flooding, with detrimental consequences for society and the environment.
There is therefore a dire need to constantly monitor water quality, as the pollution loads gathered in the Jukskei channel ultimately reach the Hartbeespoort Dam, which is already in a state of high eutrophication. In responding to these water management challenges, it is crucial to understand the relationship between land use change, rainfall trends and water quality, so that storm water runoff can be managed effectively and efficiently.
Data which was obtained from the Department of Water Affairs (DWA) for the 28 year period from 1986 to 2014, shows overall concentrations of pollutants for three sites (Site A, Site B and Site C) along the Jukskei River. This correlates inversely to the increases in average water flows at these sites. The increased water flow and increased urban land use coverage over the period may be responsible for the decrease in pollutant concentrations at these sites.
The reasons for the more marked decrease in pollutant concentrations at Site A than Site B may be that Site A is located downstream of Site B. This could be due to the increased incidence of development-related impermeable surfaces occurring in close proximity to Site B, whereas Site A is further from the urban edge. It appears that an increase in the area of impermeable surfaces over time is negatively correlated with pollutant concentrations. This would imply that increased impermeable surfaces provide increased flow into the Jukskei River and therefore allow for the dilution of pollutants entering this river. This negative correlation is expected to continue into the future and the dilution effect may possibly be enhanced with increased development of impermeable surfaces within Johannesburg, depending on other water quality inputs.
M.Sc. (Environmental Management)