Comparative Study On The Construction Of Sponge City In Old And New District In Cold Region

In recent years,with the intensification of urbanization in China,problems such as urban flooding and runoff pollution have become more and more serious,which has made the concept of sponge city widely concerned.At present,the construction of sponge cities pays more attention to the application of green infrastructure,ignoring the advantages of traditional gray infrastructure.However,the urban water environment problems in some specific areas cannot be solved well by green infrastructure alone.In this study,appropriate measures were chosen based on the climate characteristics and urban development of cities in cold regions.Then designed three construction plans for gray,green and gray-green combination for the old and new district.Based on InfoWorks ICM,the water quantity and water quality control situation before and after the construction were simulated.The construction cost,maintenance cost and land occupation of different plans were compared.The evaluation method of adaptive graygreen combination system was established by means of information entropy method and TOPSIS method.The model simulation shows that the three construction plans of the new and old town can reduce the runoff and improve the water quality to varying degrees.When the rainfall intensity is low,the green scheme and the gray-green combination scheme has better control effects on water quantity and water quality.When the rainfall intensity is high,the effect of the gray-green combination scheme is obviously better than that of pure gray or pure green.Among them,the gray-green combination scheme has the best effect on the total runoff control rate,the peak flow reduction rate,the pipeline overload control,and the waterlogging control,while the green scheme has the strongest ability to reduce pollutants.The TOPSIS evaluation system was used to evaluate the three schemes of gray,green and gray-green in the old and new district.The evaluation indicators included construction cost,maintenance cost,land occupation,water quantity and water quality control effect.It is finally determined that the green scheme consisting of concave green space,bioretention cell and permeable pavement below the new urban area is the best,and the total runoff control rate of 84.8% can be achieved when P=2a rainfall.The best comprehensive benefit of the old district is the gray-green combination scheme.The scheme will upgrade the network design return period of the current pipe network from 0.5a to 2a on the basis of green measures and storage tanks,which can be achieved when P=2a rainfall 83.1% runoff control rate.After the construction of the gray-green combination scheme,the Waterlogging point in the new and old district area decreased obviously,the overflow condition of the pipe network was improved,and the peak flow and pollutants were also effectively reduced.Through the simultaneous model simulation and TOPSIS evaluation method,the effect simulation and cost-benefit evaluation of the gray facilities and green facilities in the sponge city reconstruction in the new and old district of S city,gets the best comprehensive benefits of the new and old district.Provide reference and decisionmaking basis for the planning and construction of the sponge city in the new and old district.