| With the rapid development of urbanization,the problems of frequent waterlogging,serious water pollution,shortage of water resources and insufficient utilization of rainwater resources are becoming more and more prominent in the city.Therefore,referring to the advanced concept of rain and flood management in foreign countries,we put forward the idea of constructing "sponge city" and made some achievements through the sponge construction in the pilot cities.However,the construction of sponge city is affected by many factors,especially the core of sponge city—Low Impact Development(LID)technology has strong regional characteristics.Different natural conditions,social and economic conditions and habits of human activities will have a certain impact on it.Because of its special soil geological conditions,the construction of sponge city in collapsible loess area should take full account of the harm caused by collapsibility of loess.It is necessary to take reasonable and effective LID facilities suitable for local area,and establish a scientific scheme evaluation system.In this paper,the following research is carried out on the construction of sponge city in the collapsible loess area:(1)Combing the development of domestic and international city stormwater management concept and the related theory of collapsible loess.Analyzing the feasibility of building sponge city in collapsible loess area from the aspects of rainfall condition,urban water ecological status,social economic development and loess collapsibility risk.Combing with the specific practice of related cities and National related norms,and sum up the experience.(2)Several common domestic LID facilities are introduced in detail,and the design suggestions are given in the collapsible loess area.The collapsibility of loess is included in the selection factors of LID facilities,so as to eliminate or reduce the cost and construction quantity of collapsibility risk of loess.It indirectly reflects the influence of loess collapsibility on the selection of LID facilities,and establishes the comparison and selection table of LID facilities in collapsible loess area.In order to set up a set of evaluation system for LID program suitable for collapsible loess area,this paper chooses 8 factors,including three aspects of environmental benefits,economic benefits and social benefits,to establish AHP evaluation system.(3)The structure,function and principle of SWMM model are elaborated in detail.In order to solve the problem of low efficiency of building SWMM modeling,this paper makes full use of the advanced spatial geographic data management software ArcGIS,and builds up a geographic database that accords with SWMM.Automatically deviding subcatchment areas by using ArcGIS technology,and access to the subcatchment areas parameters such as impervious surface ratio,average slope and areas through the spatial data extraction tool.This method has higher efficiency and accuracy.(4)Choosing a campus in collapsible loess area as the study area,combining with ArcGIS technology to establish the SWMM model of the region,and the runoff coefficient method is used to calibrate the model parameters.Through the synthesis of 7 kinds of rainfall lines(P=0.65a、P=1a、P=3a、P=5a、P=10a、P=20a、P=50a)with different repetition period of the regional status quo drainage capacity assessment,the maximum drainage capacity of the regional pipe network can only to the repetition period of rainfall P=1a.Based on the reform of present pipe network,two different LID facilities reconstruction scheme are made in the study area,two reconstruction schemes under study area node overflow and overloading,pipe overloading,runoff peak and total runoff,discharge load condition and rainwater collection and utilization in 7 different rainfall conditions.Finally,combed with the simulation results and economic cost,this paper uses AHP and expert scoring method to evaluate the two schemes.The results of the evaluation show that the plan two is better than the first one. |
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