Designing sustainable drainage systems in subtropical cities: Challenges and opportunities

Sustainable urban water management requires a paradigm shift from using conventional system to drain stormwater as waste to using innovative stormwater management technique to harvest and reuse the water. Sustainable Drainage Systems (SuDS) are designed to achieve the goal. Although SuDS have been used for almost two decades, the implementation has been predominantly in temperate region. The implementation of SuDS results in a variation in water quantity and quality controls in tropical and subtropical regions, which receive more intensive and frequent rainfall events than temperate regions. To improve the reliability of SuDS in such regions, we evaluate design factors based on the site-specific context and identify sizing criteria, filter media engineering, and vegetation selection, which are critical for regulating both quantity and quality. Continuous monitoring and pre-design modeling are necessary to deliver effective design guidelines based on the rainfall-runoff profiles. Innovative design measures including modification of filter media by biochar and selection of local vegetation can enhance stormwater treatment and minimize seasonal effects such as intensive flow and distinct wet/dry periods in subtropical climates. Challenges and opportunities are highlighted for further improvement of SuDS design guidelines for subtropical areas.