Relationship of Vaal Dam high water flow and water quality from 1995 to 2010

M.Sc.The Vaal River is the main source of water supply to the central industrial, mining and metropolitan regions of South Africa, and is, therefore, strictly regulated by small dams and weirs. The Vaal Dam is the main regulator of water to the Vaal River and is of great importance as it supplies water for human consumption and also to the industrial powerhouse of South Africa. Situated at the confluence of its major tributaries, namely the Vaal and Wilge Rivers, and straddling the convergence of the borders of Gauteng, Free State and Mpumalanga provinces, the Vaal Dam is approximately 77 km south of Johannesburg. It is South Africa’s second-largest dam in terms of area, and third-largest in terms of volume, and is a key component in South Africa’s water supply infrastructure. Gauteng, as well as the surrounding provinces are reliant on it for their water supply. Water flow fluctuations are deemed to be important as they could negatively impact upon the water quality. Knowledge of the relationship between fluctuating water flows and water quality is important as strategies can then be devised on this basis to improve the freshwater situation of the country, the associated management systems, and treatment technologies. By establishing the nature of the respective relationships between high water flow and the selected water quality parameters, ways could be found of reducing the costs of water quality problems, such as eutrophication. The various relationships between high water flow and the selected water quality parameters of the Vaal Dam that were established during the course of this study are as follows: In terms of pH, the study found that in the event of a decline in the water flow, the pH value increased and the water body became more alkaline. A decrease in water flow was also found to be associated with an increase in EC. An increase in water flow was found to be associated with a decrease in pH, EC and Chlorophyll-a. An increase in water flow up to a certain level was found to be associated with an increase in nitrates, sulphates and COD