The design of urban drainage systems has traditionally aimed for cost and service objectives without considering broader socio-economic implications of design decisions. This can result in designs with unequal distributions of infrastructure services among urban communities. In this paper, we propose a design approach for multi-criteria design of urban drainage systems which combines traditional design objectives, such as reliability and cost-effectiveness, with social goals like reducing inequality in the spatial distribution of infrastructure benefits. A multi-dimensional search algorithm is linked to an urban rainfall-runoff simulation model to identify portfolios of efficient (Pareto-optimal) and spatially equitable drainage infrastructure developments. A measure of the difference in flood damage between different subregions is also considered as a decision-making aide along with other criteria. An illustrative case study shows how the design framework can help planners make trade-offs, for example between spatial equity and cost-effectiveness, when selecting future interventions in urban water systems. The results imply that traditional optimisation models can lead to inequity in spatial distribution of urban drainage infrastructure services and that equality in spatial distribution of green drainage assets does not necessarily entail fair spatial distribution of flood damage between different urban neighbourhoods.
