Water-Sensitive Urban Design (WSUD) Performance in Mitigating Urban Flooding in a Wet Tropical North Queensland Sub-Catchment

Existing wet tropical urban drainage systems often fail to accommodate runoff generated during extreme rainfall. Water-sensitive urban design (WSUD) systems have the potential to retrofit the existing urban drainage system by enhancing infiltration and retention functions. However, studies supporting this as-sumption were based on temperate or arid climatic conditions, raising questions about its relevance in wet tropical catchments. To answer these questions, this study has implemented a comprehensive modelling study of WSUD effectiveness in a tropical environment. Engineers Park, a small sub-catchment of 0.27 km2 at Saltwater Creek, Cairns, Queensland, Australia is the study site to evaluate grey and WSUD flood mitigation capabilities under major (1% AEP), moderate (20% AEP) and minor (63.2% AEP) magnitudes of rainfall. A detailed one-dimensional (1D) and coupled 1D/2D hydrodynamic model in MIKE+ were developed and deployed for this study. The results highlighted that the existing grey infrastructure within the catchment underperformed during major events resulting in high peak flows (PF) and overland flow, while minor rainfall events increased channel flow and shifted the location of flooding. In contrast, integrating WSUD with grey infrastructure reduced peak flow by, 0% to 42%, total runoff volume reduction by 0.9% to 46% and flood extent ratio by 0.3% to 1.1%. Overall, the WSUD integration positively contributed to reduced flooding in this catchment, highlighting its potential applicability in tropical catchments subject to intense rainfall events. However, careful consideration is required before over-generalization of these results, since the study area is small. However, the results of this study can be used in similar study sites by decision-makers for planning and catchment management purposes, but with careful interpretation.