| Recently,with the accelerating development of China's urbanization,urban waterlogging,huge loss of rainwater resources and water pollution has become key problems to restrict the sustainable development of cities.In order to resolve those problems,Chinese government put forward the idea of“Sponge City",which originated from "Low Impact Development(LID)Rainwater System".Sponge City can effectively relieve the urban rain-flood damage and environmental pollution problems companied with fast urbanization.Low impact development is a new choice to substitute the traditional rain-flood control system in cities.With the help of LID,city managers not only can alleviate the floods caused by rainfall runoff,but also can make full use of rainwater resources and control urban non-point source pollution,which can better meet the requirement of stormwater management in China.This thesis presents the results of urban flood control effects of 7 types of Low Impact Development(LID)rainwater system(permeable pavement,vegetative swale&rain garden,green roof,and 4 kinds of LID combination measure)in a high-density residential area within the Jiefangxi Watershed,Jinan District,Fuzhou City,Fujian Province.The flood control effects of 7 types of LID rainwater system,the flood control effects under the combination of green infrastructure and gray infrastructure and the influence on LID control effects under different drainage network layout types were simulated by LID model in the PCSWMM 2015 under different rainfall characteristics(rainfall return periods,rainfall durations and rain peak positions)and extreme rainfall condition(Typhoon Longwang).The research results have a certain applicability for other regions of different rainfall characteristics,and have a certain guiding functions and reference values in screening the optional choices from two types of stormwater drainage network layout and the LID measures in the process of sponge city construction.The main results in the thesis are listed as follows:(1)Stormwater model in the study area was built by using PCSWMM model,and modified Morris screening method was used for the sensitivity analysis of water quality parameters,hydrological and hydraulic parameters of the model.Integrated runoff coefficient was chosen as the objective function to calibrate the high-sensitive parameters.The thesis designed 7 types of LID rainwater system.According to the rainstorm intensity formula of Fuzhou City and the Chicago rainfall process model(CHM)to synthesize different rainfall scenarios with rainfall return periods,rainfall durations,rainfall peak positions and the extreme weather of Typhoon Longwang.(2)The research results of surface runoff and rain-flood characteristics showed that:with the increasing of the rainfall return periods,the surface runoff depth and the runoff coefficient of the study area increased constantly,and the northwest community of the study area was most seriously affected.Decreasing the rainfall return periods and increasing the rainfall durations brought certain relief on the runoff quantity and water quality of the affected community.The influence of the change of rain peak positions on surface runoff was not obvious.After taking 7 types of LID rainwater system in the northwest community,runoff quantity and water quality were under control,and the best control result was achieved in a long rainfall duration scenario combined with a low rainfall recurrence interval.After performing a cost effectiveness analysis on different LID rainwater system,it was found that the permeable pavement,the combination measure of permeable pavement and vegetative swale&rain garden and the combination measure of permeable pavement and green roof had the best control effects on the runoff quantity and water quality in terms of unit cost,and they all belonged to low cost and high efficiency measures.(3)The research results of waterlogging node indicated that:with the increasing of rainfall return periods,the maximum calculated surface water depth and the number of waterlogging nodes in study area continually increased,especially in the northwest community.Changing rainfall characteristics(decreasing rainfall return period,increasing rainfall duration,backward shifting of rainfall peak)had a positive significance to alleviate waterlogging situation and reduce non-point source pollution load in the northwest community.The flood situation of waterlogging nodes had been effectively controlled after taking single LID layouts and combined LID layouts under different rainfall characteristics.Time to reach maximum depth in waterlogging nodes was postponed,and duration time of maximum depth in waterlogging nodes was shortened.The peak flow was reduced,with shortened flood time and decreased seeper depth.Peak SS concentration has been controlled and the peak time of SS concentration was postponed.The reduction effect on flood by different LID was more significant under the longer rainfall durations combined with lower rainfall return periods.(4)The research results of sewer flow simulation showed that:all kinds of LID had a certain reduction effect on peak sewer flow,peak SS concentration and peak time of SS concentration under different rainfall characteristics,while the effect of LID on sewer full-flow durations and the peak time of sewer flow was not obvious.(5)The research results of LID flood control effects under the extreme precipitation condition showed that:LID relieved the waterlogging situation of the northwest community effectively in the Typhoon Longwang scenario which was a short-duration and high-intensity extreme rainfall scenario.In the extreme rainfall weather condition,the flood control effect of LIDs on serious waterlogging node was relatively poor,which meant that green infrastructure couldn't alleviate waterlogging situation effectively in extreme rainfall scenario.The better method to effectively alleviate waterlogging is combining green infrastructure with gray infrastructure,which called for more research.(6)The research results of the influence on flood control effects of different drainage network layouts showed that:the orthogonal and parallel stormwater drainage layout had no influence on surface runoff depth and SS load in runoff,but they had a certain effect on peak flow and peak SS concentration under different rainfall characteristics.The effects of LIDs in the two stormwater drainage network layout types on outlet peak flow and peak SS concentration were different under same rainfall characteristics.The parallel type had less peak flow and higher peak SS concentration than orthogonal type.When in small rainfall return period,long rainfall duration and early rain peak occurrence,the effects of LIDs on outlet peak flow under parallel type was better than orthogonal type.Under different rainfall characteristics,the effects of permeable pavement,green roof and LID combination with parallel type on outlet peak SS concentration were better,and the effects of vegetative swale&rain garden on outlet peak SS concentration with orthogonal type were better.Under extreme rainfall condition,the flood control effect of LIDs with different stormwater drainage layout types was more sensitive to rainfall duration,and the control effect of LID combination with parallel type was better.(7)From the results of flood control effect,within the combination of LIDs,the best combination is permeable pavement and vegetative swale&rain garden and green roof;when using single control measure,the best one is permeable pavement.Flood control effect of combination of LIDs is better than any single LID measure in the combination.From the flood control effect of the LID per unit area,permeable pavement is the best to relieve the waterlogging.The combination measure of permeable pavement and vegetative swale&rain garden and the combination measure of permeable pavement and green roof achieve a good flood control effect in the whole layout and per unit area. |
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