Optimization And Resilience Enhancement Of Urban Grey-green Infrastructure Systems

Recent studies have shown that considering grey infrastructure coupled with green infrastructure may be a promising new way in urban stormwater management.However,there is still a lack of a comprehensive optimization and resilience assessment method for this emerging grey-green infrastructure system in the face of potential hydrological risks over its life cycle,which limits the planning and implementation of urban drainage systems,especially in high-density urban areas that are extremely sensitive to hydrological risks.In this regard,this study selects Guangzhou Pearl River New Town as the case study,and firstly proposes an innovative optimization-evaluation framework,which optimizes the layout of grey-green infrastructure with different degrees of decentralization under the constraint of hydraulic reliability with the goal of life-cycle cost,and divides the resilience evaluation system into technical resilience and operational resilience:Technical resilience refers to the physical integrity of a system under exogenous threats caused by environmental changes and extreme weather.Operational resilience refers to the functional degree and ability of the system structure to operate safely under abnormal load conditions such as facility and functional deterioration.Furthermore,in order to consider the internal(self-structural)uncertainty of grey-green infrastructure systems during their life cycle,the possibility of grey infrastructure failure degree and the long-term performance degradation of green infrastructure were quantified for the risk scenario of operational resilience assessment.In addition,the initial optimization-evaluation framework is extended to an optimization-evaluation-decision framework by introducing a multi-criteria decision-making method.Finally,this study integrates life-cycle cost,technical resilience and operational resilience into a multi-objective optimization model,which optimizes the allocation of the decentralization degree of pipeline network layout,the construction area,scale and type of grey-green infrastructure.The solution of the best trade-off between the corresponding grey-green coupling degree and the optimization objective is established,and the detailed spatial design is carried out for the real site.The results show that compared with the traditional grey-only system,the grey-green coupling strategy provides better hydrological performance in terms of peak flow and peak delay time,and is more economically competitive.In terms of resilience,the grey-green system is better able to withstand most rainstorm scenarios,that is,higher technical resilience,but performs less well under extreme intensity and prolonged rainstorm events.In terms of operational resilience,the grey-green system can deal with part of the pipeline network failure scenario more calmly.However,after considering the grey infrastructure failure probability over the lifetime as well as the performance degradation of green infrastructure,the results show that the resilience of grey-green systems is overestimated.Even so,it still has a longer operating life than the grey system in most design rainstorms,but may not perform well in extreme rainstorm scenarios.The grey-green infrastructure strategy with multi-objective optimization is superior to the traditional grey-only system in terms of cost and resilience.The grey-green scheme with resilience preference can bring a large degree of resilience enhancement with only a slight cost increase.With the improvement of green infrastructure optimization variables in multi-objective optimization,the life-cycle cost of grey-green solutions can be further reduced,especially for cost-preferred solutions.On the other hand,the centralized layout has higher technical resilience but lower operational resilience than the decentralized layout.However,when the grey and green infrastructure structures within the grey-green system have been severely damaged,the degree of resilience enhancement is not sensitive to the degree of decentralization of the layout.For the same available area,bioretention cells attenuated surface runoff better than permeable pavement.Therefore,bioretention cells may be more suitable for urban areas with dense buildings and a shortage of open space.This research framework can be used to support the urban drainage system planning and hydrological risk management,which can help promote the construction of sponge cities and resilient cities.