Abstract
Sustainable urban drainage systems are multi-functional nature-based solutions that can facilitate flood management in urban catchments while improving stormwater runoff quality. Traditionally, the evaluation of the performance of sustainable drainage infrastructure has been limited to a narrow set of design objectives to simplify their implementation and decision-making process. In this study, the spatial design of sustainable urban drainage systems is optimized considering five objective functions, including minimization of flood volume, flood duration, average peak runoff, total suspended solids, and capital cost. This allows selecting an ensemble of admissible portfolios that best trade-off capital costs and the other important urban drainage services. The impact of the average surface slope of the urban catchment on the optimal design solutions is discussed in terms of spatial distribution of sustainable drainage types. Results show that different subcatchment slopes result in non-uniform distributional designs of sustainable urban drainage systems, with higher capital costs and larger surface areas of green assets associated with steeper slopes. This has two implications. First, urban areas with different surface slopes should not have a one-size-fits-all design policy. Second, spatial equality must be taken into account when applying optimization models to urban subcatchments with different surface slopes to avoid unequal distribution of environmental and human health co-benefits associated with green drainage infrastructure.
Highlights
Global climate change, rapid expansion of cities, and the aging of existing urban drainage infrastructure raise new challenges for urban flood management (Raei et al 2019; Arfa et al 2021)
Alves et al (2019) investigated benefits of synergetic use of green, blue, and grey drainage infrastructure facilities for flood management designs. They showed that flood mitigation objectives and environmental co-benefits of sustainable drainage infrastructure must be jointly taken into account in optimization models to maximize efficiency of sustainable urban drainage systems
Large cities are usually characterized by spatial variations of surface slopes, affecting infiltration and detention patterns of stormwater runoff
Summary
Rapid expansion of cities, and the aging of existing urban drainage infrastructure raise new challenges for urban flood management (Raei et al 2019; Arfa et al 2021). Drainage systems have been designed using trial-and-error approaches resulting in poor project outcomes that often fail to achieve an appropriate balance of community’s interests To overcome this problem, researchers have linked rainfall-runoff simulation models with multi-objective optimization methods for multi-dimensionally efficient (‘Pareto-optimal’) urban drainage system designs. Alves et al (2019) investigated benefits of synergetic use of green, blue, and grey drainage infrastructure facilities for flood management designs They showed that flood mitigation objectives and environmental co-benefits of sustainable drainage infrastructure must be jointly taken into account in optimization models to maximize efficiency of sustainable urban drainage systems. This needs to consider the relative efficiency of grey and green drainage infrastructure in reducing flood damage and stormwater pollution (Yang and Zhang 2021), in line with the
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