Research On Index Decompositiom Method Of SWMM Assisted Sponge City Special Planning

The rigid index of planning control(i.e.Total Annual Runoff Control Rate,TARCR for short)in The Technical Guide to the Sponge City Construction--Low Impact Development Of the Rainwater System(try out)(hereinafter referred to as The Guide)provides a quantitative standard for the construction direction and effect of sponge city.In addition,The Guide points out that,in the process of compiling or revising the Special Planning for Sponge City,by the methods of trial algorithm or model simulation,the rigid index can be decomposed into some guiding indexes,including the proportion of the sunken green space,the rate of the permeable pavement,etc.Thus,the TARCR can be quantified step by step to the coverage of the LID facilities in different plots,making it more practical for the urban planning,design,construction,and assessment.It has only been five years,however,since the first batch of pilot cities were identified in the construction of Sponge Cities in China.And The Guide is still in the trial stage,with little detailed explanation for how the rigid index is decomposed by the method of model simulation,what the specific steps of the decomposition are,and which simulation software is applicable,and there are few hydrologic and hydraulic simulation studies with Storm WaterManagement Model(hereinafter referred to as SWMM model)as the typical representative in China.Therefore,how to use the model simulation technology to decompose the rigid index and guiding index of Sponge City Planning Control more scientifically has become an urgent issue at present.This research,with the aid of SWMM model and Pingxiang urban area as the case,figured out an approach to decompose indexes by the methods of trial algorithm or model simulation.By collecting,processing and interpreting the current background data of precipitation data,rainwater evaporation data,elevation data and impermeable surface area in Pingxiang city,the SWMM model of this research area was established.In the evaluation phase of the current TARCR,simulation and evaluation were carried out to obtain the current TARCR of each block in Pingxiang city based on the established SWMM model's capacity of management and control on the current TARCR of each block in the research area,identifying the weak areas of runoff control and providing an important quantitative basis for the TARCR of all kinds of land use in cities.The rigid index decomposition,based on the current situation of the TARCR in each district of Pingxiang city and the TARCR decomposed to various kinds of land in Pingxiang city by volumetric method of The Guide,established appropriate annual runoff control objectives for all types of land use and put forward mandatory runoff control requirements for later land development and construction.In the guiding index decomposition stage,the sunken green land and permeable pavement were selected as the main LIDfacilities by considering the economic conditions,land use nature,climate characteristics and underlying surface of Pingxiang city,and with the help of the LID facility simulation module in the SWMM model,the planning annual runoff control rate of all kinds of urban land was further decomposed into the sunken green land rate and permeable pavement rate of each block,making the annual runoff control objectives for all types of land use in Pingxiang city more substantial.The results of index decomposition showed that this method could provide some ideas and references for the further development of Special Planning for Sponge City and the improvement of the Guide.