Analysis Of LID Rain Flood Control Effect And Optimal Reformation Of Sponge Campus Under Different Rain Patterns

In recent years,with the acceleration of industrialization and urbanization,the permeable nature of the underlying surface of cities has changed,and the global atmosphere has Weather changes have greatly increased the probability of extreme rainstorms.The problem of urban waterlogging in china has gradually become prominent.To solve this problem,china has proposed the concept of "sponge cities",and alleviate urban waterlogging through the construction of low-impact development measures(LID).The study area selected for this study is a typical college in Xi’an city,combined with five common design rainstorm patterns,used the SWMM model to study the campuse that has built LID under the conditions of different design rain patterns and different rainfall return periods.The current rain and flood control effects are analyzed and its shortcomings and improvement directions are analyzed.After reasonable optimization and improvement,three LID combination schemes were designed and simulated.The research comprehensively analyzed the rain flood control effect of the existing LID measures and the optimized three LID schemes under five different rain patterns,as well as the influence of different rain pattern choices and different rainfall return periods on the LID control effect,and determined the most unfavorable rain pattern in the study area,and finally through the analysis of the relationship between the LID storm flood control effect and the reconstruction cost,the optimal cost-effective combination plan that is most suitable for the study area is selected.The main research results are as follows:(1)Derived the rainfall data of five rainstorm types(Chicago、Huff-2、Pilgrim & Cordery、Triangl、Rectangular)with a rainfall duration of 120 min and a return period of 1a,5a,10 a,and 50 a.(2)This study used the addition of a reduction state model to compare and analyze the current LID and reduction model rainwater simulation effects under different design rain patterns and different return periods,and concluded that the current LID measures and reservoirs have the ability to control storm floods,but the effect of rain and flood regulation is limited.And it is found that the current LID control effect is not good,but the effect of the reservoir is better,so the reservoir should be retained and the current LID measures should be further optimized.(3)The three LID combinations optimized in the research have significantly enhanced the effect of storm flood control compared with the current LID.The three schemes under the five rain patterns are ranked as the first option in terms of surface runoff control effect and rainwater pipe network efficiency control effect.Scheme one(Permeable + Rain Garden +Sunken Green Space + Green Roof)> Scheme Three(Permeable + Rain Garden + Green Roof + Rain Barrel)> Scheme Two(Permeable + Rain Garden + Sunken Green Space + Rain Barrel).Scheme 1 and Scheme 3 have a large difference in area,but the effect of rain and flood regulation is similar,which benefits from the good effect of the rain bucket in Scheme 3.This paper analyzed the cost of reconstruction per 1% of surface runoff reduction rate and 1%of peak flow reduction rate under each plan,and finally determined the most cost-effective plan suitable for the study area,which is the Scheme 3.(4)Different design rain patterns result in different characteristics and amounts of runoff due to their different rain pattern characteristics,which ultimately leads to differences in the total and peak amount of runoff reduction,the value of the runoff coefficient,and the efficiency of the drainage network.The analysis shows that the Chicago rain pattern and Pilgrim & Cordery rain pattern are the more unfavorable rain patterns in the study area.According to the actual situation or target situation,one of them can be selected as the design rain pattern for pre-evaluation of the design of the area and rainwater system.This study provides a certain reference value for the reconstruction of the sponge campus in the old campus,and the study of selecting the appropriate design rain pattern based on the target situation analysis in the areas with insufficient precipitation data.