Estimation of Nutrient Load for Effective Water Resource Management in Dams: A case study of the Roodeplaat Dam, Southern Africa

Poorly treated domestic wastewater and diffuse nutrient loading from agriculture and informal human settlements greatly threaten water resources due to the alteration of ecosystem function and the reduction of the water’s fitness for use. Thus, the aim of the study was to assess nutrient loading in the eutrophic Roodeplaat Dam (RD) to inform water resource management as a foundation for the rehabilitation of the dam. The objectives were to determine Total Phosphorus (TP) and Nitrogen (N) loading capacity into the RD as well as to propose a total mean annual nutrient reduction for the sustainability of the dam. Flow Duration Curves and Load Duration Curves were employed as analytical tools. It was observed from the study N and TP varied significantly among the sites investigated and the actual TP loads were significantly higher than the allowable load throughout the study area. The study further observed that nutrient loading was more prominent during low flows due to the reduced dilution effect. Thus, this study recommended the application of nature-based solutions to control pollution and reduce stormwater and runoff input, as well as employing low-cost green treatment technology options to reduce nutrient loads from domestic wastewater effluent in municipal wastewater treatment pond systems, which requires less energy. Stringent point source pollution control measures were further recommended, and that water quality planning should consider the desired beneficial water use per catchment, considering the impactors.