Study On Sponge Resilience Evaluation And Improvement In Old City

In recent years,due to the impact of global warming and high-speed urbanization,the increase of hard pavement and the increase of surface runoff lead to frequent urban waterlogging and serious water pollution.The old city is densely built and the design standard of rainwater system is low,which makes waterlogging and environmental problems more frequent.In view of these problems,the concept of "sponge city" has been well applied.This paper mainly focuses on the sponge resilience evaluation and resilience improvement in the old city.The sponge resilience is represented by the ability of cities to cope with flood disasters and runoff pollution.An evaluation system of sponge toughness in old city is established.Taking Xiaozhai area of Xi’an city as an example,the sponge resilience is evaluated and improved by optimizing the configuration of sponge facilities,in order to provide a method of evaluation system establishment and facility optimization for sponge city construction.The main conclusions are as follows:(1)The principle and modeling method of SWMM(Storm Water Management Model)are described,and the SWMM model of stormwater drainage system in the study area is constructed.The model is verified by runoff coefficient method,which can be used to simulate the research area.The SWMM model is used to simulate the study area under different return periods,and the effects of water quantity and quality are analyzed.According to the analysis results,under the condition of high rainfall return period,the runoff control effect in the study area is poor,which makes the study area prone to waterlogging.(2)The evaluation index system of sponge resilience in the old urban area is established to provide a method reference for the evaluation of sponge resilience in the old urban area.Based on the analysis of basic conditions of Xiaozhai area in Xi ’an,a total of 10 indexes are selected from engineering,environmental and social levels,and the index weights are determined based on AHP-entropy weight method.The sponge resilience in the study area is evaluated based on the constructed index system.The evaluation results showed that the sponge resilience is strong only under the rainfall during the la return period,and poor when the rainfall exceeded the la return period.In order to solve the existing problems in the study area,it is proposed that the sponge resilience should be improved by different gray-green facility configuration schemes under different rainfall scales to meet the objectives of water ecology,water environment and water security.(3)40 scenarios of single green facilities(Low impact development facilities)and 25 scenarios of grey facilities(stormwater pipe network and storage pool)are designed.The effects of surface runoff,pollution load and other water quantity and quality under different layout schemes are analyzed,and the key indicators affecting the effect of runoff control under each layout scenario are identified.For LID facilities,increasing the proportion of layout has a better effect on runoff control rate and pollutant reduction,and the four facilities have the best effect compared with rain garden,while the green roof has the worst effect.For rainwater pipe network,increasing pipe diameter can increase drainage capacity of rainwater system and reduce overflow.It has a good effect on relieving overloaded nodes and pipe segments.For the storage pool,the more dispersed the distribution of the storage pool,the better the regulation effect on water quantity.The larger the volume of the storage pool is,the better the regulation effect on water quantity is.(4)Based on the objectives of water ecology and water environment,drainage safety and waterlogging safety,the multi-objective optimization model are established under different rainfall scales,and the optimal allocation scheme of grey-green facilities under different rainfall scales is determined by the ideal point method.The results show that:4.18%rainwater garden+10.82%sunken green space+7.48%permeable pavement+2.52%green roof+45%pipe diameter expansion ratio+350m3 standard for setting the capacity of storage pools per 10,000 m2 hardened area is the optimal layout scheme of the study area.The resilience of sponges in the study area is evaluated under the optimal scheme.The evaluation results show that LID facilities,pipe network system,and storage pool play a role at the same time.Under this scheme,the resilience of sponge in the study area is greatly improved compared with the current situation,and it has a strong ability to cope with waterlogging and pollution,and can meet the requirements of water ecology,water environment,drainage safety,and waterlogging safety goals.