Effectiveness of bioretention system and vegetated swale for reducing urban flood risk in equatorial region: a case study in Kuching, Malaysia

One of the main causes of urban inundation is the rise of impermeable surfaces brought on by increasing urbanization. Low impact development (LID) practices have been employed in previous studies to mitigate urban flooding. However, the effectiveness of LID practices in reducing runoff peaks and improving water quality is unknown, especially in the equatorial region. This study explored nine alternative scenarios to evaluate the effectiveness of the bioretention system and vegetated swale using the Storm Water Management Model (SWMM). Using precipitation data of December 2021, the Swinburne University of Technology Sarawak Campus has been chosen as the case study. The findings demonstrated that these two LID practices could significantly lessen urban flooding. Under scenario 7, the combination of 28.4% bioretention system and 11.3% vegetated swale reduced the maximum runoff peaks by 22.98% at Peak A, 24.71% at Peak B, and 24.09% at Peak C. In the meantime, under scenario 7, the implemented LID practice has removed 20.09% of TSS, 19.75% of TP, and 12.26% of TN. It was discovered that runoff peak reduction increases as the area covered by vegetated swale and bioretention system increases. The outcomes showed that bioretention system performed better than the vegetated swale in reducing peak runoff and enhancing water quality. Local authorities can use the findings of this study to offer recommendations for reducing disaster risk, controlling urban flooding, and revitalizing urban areas.