An Optimization And Evaluation On The Combination Scheme Of Gray-green Infrastructure Based On SWMM

The conditions of city underlying surface have been changed significantly with the rapid development of urbanization.It has caused a series of problems such as urban waterlogging and water pollution.The sponge city construction has become a new method to solve or alleviate these problems as it reduces surface runoff and non-point source pollution.However,the existing studies related to sponge city mainly focuses on the imitation of green infrastructure,whereas the costs were not reasonably considered in developing optimization schemes,and the comprehensive effect evaluation methods on sponge city construction schemes are not yet studied.Therefore,it is urgent to explore an effective mechanism on combination of green and gray infrastructure in the construction of sponge cities,so as to make use of the advantages of the both infrastructures,and to develop optimal construction scheme according to the local financial situations and real demands.In this study,a residential community in Jiaxing of Southern China was taken as study area.The effects of green and gray infrastructure were evaluated using the storm water management model(SWMM).The impact of each type of green or gray infrastructure on the efficiency was analyzed.Then permeable pavement,sunken green space,rain garden,green roof and storage tank were combined to simulate the effect on the reduction of storm water and pollution,where each type of infrastructure was set at the proportion of 0% to 100%(increased by 10%).Accordingly,9 schemes were developed with 4 types of infrastructure,namely,single type of green infrastructure,single type of gray infrastructure,combination of various green infrastructure and green-with-gray infrastructure combination.Then the results were simulated under the rainfall reappearing periods of 1a,2a and 5a.The control effect on water quantity and quality of each scheme was analyzed,and cost-effectiveness analysis was fulfilled for each rainwater management scheme using a life cycle cost evaluation method.Finally,a TOPSIS(technique for order preference by similarity to ideal solution)evaluation method was introduced to carry out a multi-criteria decision considering 4 indicators such as the total runoff control rate,the peak discharge reduction rate,the pollutant removal rate and the economic cost.The weights of cost indices were set as different values,so that the ranking of effectiveness in each scheme is obtained under different cost weight in case of 2a rainfall.The results showed that:(1)marginal utility existed in the effect of single rainwater management method on rainwater management;(2)the schemes of green-with-gray infrastructure combination and combination of various green infrastructure were optimal schemes on controlling water quantity and quality;(3)the cost weights had significant impacts on multi-criteria decisions,and all schemes could be classified as 4 types such as efficiency type,cost type and stability type.The green-with-gray infrastructure combination schemes were optimal schemes without considering the cost factors,whereas the single type of green infrastructure scheme was optimal scheme considering the cost.The methods and technical of this thesis could support for the sponge city builders and water resource managers in the rapid urbanization areas.