Research On The Accessibility Of Sponge City Construction Planning Indexesin Jiangxia Districtof Wuhan

Since the beginning of China’s sponge city pilot construction in 2015,all pilot cities have completed the construction of regional pilot project,and a new round of large-scale sponge city construction is about to begin.In such process,many problems have been highlighted,among which the toughest one is that,during the formulating of the construction plan of sponge cities,most of the accessible assessments of water element indexes still use qualitative analysis or simple accounting,and the assessment results are not accurate enough.Taking Jiangxia District of Wuhan as an example,this paper uses the methods of theoretical research,quantitative analysis and software model simulation to analyze the accessibility of the constraint indexes for three water elements,including the drainage capacity of pipe network,the prevention and control capacity of waterlogging for water security,the control rate of total annual runoff for water ecology,and the reduction rate of non-point source pollution for water environment.At the same time,this paper puts forward the targeted improvement plan for the non-conforming parts,which can provide technical support for the compilation of the sponge city construction planning in Jiangxia District,as well as reference for the comprehensive implementation of the sponge city construction planning in Wuhan and even the whole country.The main work and conclusions of this paper are as follow:(1)This paper simulates the target area under five different recurring design rain events through InfoWorksICM software.The analysis of the pipeline overload results shows that the proportion of overloaded pipeline sections is 0,7.70%,24.09%,36.34%,and 46.35%.There are 5 sections of pipelines whose drainage capacity does not meet 2a,and 3 of them are overloaded due to their own insufficient drainage capacity,while the other 2 sections are overloaded due to insufficient drainage capacity of downstream pipelines.(2)Coupling 1D pipe simulation results with 2D flooding model,it is found that there are 6 flooding points with flooding depth greater than 0.15m under 20a condition,among which the maximum flooding depth is 0.754m and the longest flooding time is more than 120min.An improvement plan is made for these 6 inundation points which can not meet the planning requirements.(3)The total annual runoff control rate index is simulated by InfoWorks ICM software under the actual rainfall data of 2013.The result of index analysis by value assignment method is 73.2%,which can not meet the target value of annual total runoff control rate of 75%.And using the volume method to analyze the storage of various types of land accurately,the total control rate of annual runoff after simulation is 72.6%,and the additional storage needed to achieve the target of 75%is calculated as 8861m~3.(4)The pollutant loads of TSS,TN and TP in the target area under the three rain intervals of medium rain,heavy rain and rainstorm are calculated using the pollution load modulus method.The results are 99.43t/a,26.00t/a and 1.90t/a respectively.Finally,the TSS and TP reduction in target area are 82.28t/a and 3.77t/a,and the corresponding non-point source pollution reduction rate is 82.75%,which can meet the requirements of sponge city construction planning.