Designing and engineering nature-based solutions - An evaluation of sustainable drainage systems for improving stormwater quality in Johannesburg, South Africa

Climate change and rapid urbanisation exacerbate water management challenges leading to increased risks such as floods, droughts, and deteriorating water quality. As urban areas expand, particularly in regions like Southern Africa, the demand for effective stormwater management grows. Conventional stormwater infrastructure, while addressing runoff, is often associated with increased impermeability and exacerbated environmental issues. Consequently, there is a pressing need for alternative approaches that consider ecological balance and resilience. Nature-based Solutions (NBS), such as Sustainable Drainage Systems (SuDS), offer a pathway towards more water-sensitive futures. This study evaluates the effectiveness of SuDS by comparing two sites in Johannesburg, South Africa with distinctly different design approaches: The Reid, a private brownfield residential development, and Observatory, which is a city-owned golf course. The findings reveal that thoughtful planning and design of SuDS can significantly enhance stormwater quality, as demonstrated by The Reid's superior performance. In contrast, Observatory's less effective design highlights missed opportunities and underscores the importance of informed design choices as well as the need to strengthen local governments’ technical and governance capacity in the realisation of urban NBS such as SuDS. A key difference is The Reid’s larger water retention volume and longer hydraulic retention time (HRT), which enable crucial biogeochemical processes essential for water quality improvement. In conclusion, while SuDS offer significant environmental benefits, including improved water quality, flood attenuation, and increased biodiversity, their effectiveness hinges on careful design and maintenance. The study underscores the necessity of adopting well-planned SuDS solutions to maximise their impact and address the complex challenges of modern urban water management.