A water sensitive urban design (WSUD) planning framework for catchment-scale urban pluvial flood mitigation targets

Water Sensitive Urban Design (WSUD) offers a promising solution for urban pluvial flood mitigation. While the existing target-oriented approach is effective for rapid WSUD planning for stormwater quality and quantity control, it struggles with pluvial flooding reduction objectives due to the complex interactions with stormwater drainage networks across a catchment. We propose a novel framework that advances WSUD planning for flood mitigation by generating a pool of cost-effective strategies aimed at reducing flood damage return periods. These target-driven strategies involve the strategic placement of WSUD across the catchment with detailed designs to achieve maximum flood damage reduction, using newly generated design curves that link WSUD's effective storage capacity to its performance in runoff volume reduction. Application of this framework to an urban catchment in Sydney, Australia demonstrated high success rates of WSUD strategies that maximised flood volume reduction at equivalent costs, effectively achieving four flood mitigation targets. Life-cycle cost-benefit analysis highlighted the importance of adequate bioretention storage capacity for long-term cost-effectiveness, and suggested aligning WSUD planning with existing drainage network capacity for optimal economic outcomes. The substantial variations in WSUD configurations among the cost-effective strategies underscore the framework's ability to provide flexible strategies for meeting unique subcatchment conditions and diverse stakeholder needs. The framework serves as a valuable tool for realising exploratory WSUD planning, with strong adaptability to diverse catchments, climates and future conditions, helping to maximise WSUD's flood mitigation potential.