Multi-level Decomposition Research On Control Index Of Sponge City Construction From The Perspective Of Flood Resilience

At the background of frequent urban flooding in China,the decomposed implementation of sponge city targets at each level of planning will directly affect the effect of urban flood control,which is a hot topic in the planning field.However,the standard value of annual runoff control area given in Technical Guidelines for Sponge City Construction has a long span,and the decomposition method is directly decomposed from city to area,which makes it difficult to guide stormwater control in block.The relevant planning practice is based on qualitative prediction index of standard value,and less on the current situation of storage volume estimation to formulate suitability index,resulting in single index homogeneity and resource wave of facility construction.Therefore,based on the existing sponge city construction control index system and the decomposition method of ann ual total runoff control target,this paper attempts to explore a method of multi-level decomposition of regional construction target into catchment area and block unit through calculat ion of storage volume layer to improve the effect of stormwater control.This paper starts with the theoretical analysis of flood resilience and sponge city,making a comparative analysis of their similarities and differences,so as to clarify the importance of construction control index and the direction to be improved of t he current sponge city.Then,based on the analysis of the content and decomposition method of sponge city construction control index,putting forward the principle of decomposing and optimizing the control index of sponge city from the resilience perspective,namely: taking rainfall control as the core,effective control the small ?medium and extreme rains as the goal,the current status of land leachability assessment as the basis,the multi-level decomposition of indicatorsas as the way,the rain flood control evaluation as the validation,redundancy index regulation as the feedback mechanisms,the multi-level decomposition of the annual total runoff control target is transformed into planning and construction indexes,finally implementted to the planning plot scale.Then,with the Hongye sponge city model,based on the technical guide for sponge city construction and the principle of hierarchical decomposition optimization,putting forward a set of sponge urban construction control index decomposed to "city-catchment units-plot" scale,the method of decomposition process includes: the evaluation of land rainwater storage capacity,multi-level decomposition calculation of indicators,the evaluation of flood control and perfection of index control.Finally,selecting Fenghuang county of sponge urban construction demonstration area in Hunan province as the typical research area,after analyzing the sponge city construction conditions and requirements,using the proposed method to get the planning and construction indexes such as the sunken green rate,which can be connected with the green rate and building density index,and finally putting forward the proposal of implement and layout.After summarizing the research conclusions,it is found that under the influence of the current situation of the plot's storage capacity,the total annual runoff control target presents an unbalanced distribution state in the index transmission process,but as long as the whole plot reaches the regional target value,it can still effectively control medium and small rainfall.The construction index with the annual total runoff control rate as the target cannot completely control the surface water under the rainstorm scenario,and the configuration of "gray sponge" facilities cannot be ignored.This paper focuses on the connection between low-impact development index with the green rate and the building density index under the medium and small rainfall,as well as supplement and consummation of storage volume index of grey facility u nder extreme rainstorm.The proposed multi-level decomposition method,although still needs to be improved,but still has reference value which can provide a reference for the implementation of sponge city construction control index in planning.At the same time,trying to combine the theory of flood resilicense with the construction of sponge city in order to provide meaningful value for the rain-flood control of sponge city.