Research On The Decomposition Method Of Sponge City Detailed Control Plan Indicator

Sponge city is not only a "conceptual transformation" of the overall development model driven by the urban construction model,but also a "green way" to systematically deal with the urban water resources,water security,water environment and water ecology.In the sponge city urban plan system,the management and control in the phase of detailed control plan plays a vital role,and there are still some deficiencies in the current research and practice.On the one hand,there are some differences in the management mechanism of detailed control plan in different cities,and it is impossible to form a unified indicator system and control standard for sponge cities.On the other hand,there is no reliable technical approach to implement sponge city indicators in detailed control plan phase,and there are often cases where indicators are difficult to implement.Hunan province is located in a rainy hilly area of southern China and has its own specific detailed control plan system and natural geographical characteristics.It is necessary to take the regional characteristics into the consideration of construction and decomposition of the detailed control plan indicator system of sponge city in Hunan province.In this article,by combing the relevant theories and planning cases of domestic sponge cities,drawing on the practical experience from the stormwater management in foreign countries,and analysing the implementing methods and planning difficulties of sponge city,exploring a detailed control plan ideas of sponge city that suitable for Hunan province,puts forward to pay attention to hydrological characteristics,by improving the control and zoning methods and adding a series of related indicators to conduct and decompose the sponge city target layer by layer,to build three levels and two types of indicator system.The three levels are control unit level,drainage zoning level and plot level,and the two types are mandatory indicator and guiding indicator.The total annual runoff control rate is the core indicator of sponge city,and its rational decomposition is a major difficulty in planning.In this paper,it is proposed that the total annual runoff control rate should be transformed into a directly decomposable control volume indicator,and then according to the current construction situation in each drainage zone and the characteristics of various plot,innovatively using the entropy method in the objective weighting method to evaluate the suitability of sponge city construction.Through the calculation of the entropy value and weight of the multi-factor indicator,the core content of the control volume ratio of each drainage zone and the control volume decomposition ratio of each type of land is obtained.On this basis,the control volume is used as a calculable and quantifiable mandatory indicator to control and guide the planning and construction.Finally,combined with the conclusion of suitability evaluation,reasonably formulate the proportion and combination form of low-impact development facilities.The actual control volume of the low-impact development facility is calculated by weighting,and the corresponding target requirements are met step by step by checking calculation and adjustment.This paper makes an empirical study on the sponge city detailed control plan in Shahe district of Ningxiang city,and through carrying out the hydrological simulation of the past 3 year’s real rainfall conditions,using SWMM model to verify whether all kinds of low-impact development facilities can meet the requirement of total annual runoff control rate or not.From the verification conclusion,the indicator system and decomposition method proposed in this paper can meet the requirement of overall indicator and provide reference for the compilation and indicator decomposition of the sponge city detailed control plan in the same type area.