Evaluating the impact of indigenous ground cover categories in reducing stormwater runoff within bioswales in South Africa

Abstract

Urbanization has placed pressure on urban stormwater infrastructure. Previously implemented stormwater master planning had become inadequate in managing floods. Research has shown that the use of sustainable drainage systems (SuDS) assists in mitigating the effects of the change in impervious areas brought about by urbanisation. While research on the usage and functions of SuDS is widely available, there is a lack of literature on the impact of indigenous ground cover categories in reducing stormwater runoff within bioswales in South Africa. The aim of this study was to evaluate the impact of indigenous ground cover categories on the hydrological performance of a bioswale in reducing stormwater runoff volume and peak. A physical simulation model was constructed to assess the water balance of the bioswale, taking into account the soil water content of the engineered soil medium. The effects of the inflows in the simulation model were addressed by mimicking the 1-in-10-year post-development return period stormwater runoff scenario, within the Gauteng Province, South Africa, during the summer rainfall pattern. The lawn category (kweek /Cynodon grass) demonstrated an average volume reduction of 54.7%, with a peak flow reduction of 49.9%. Ornamental grasses and veld grasses also exhibited a volume reduction (42.2% and 38.0%, respectively) and peak flow reduction (40.4% and 38.3%, respectively). Additionally, these grass categories influenced the soil water content. Overall, these findings demonstrate that there is potential for various grass types to mitigate stormwater runoff.