The Simulation Study On Grass Swale’ Infiltration And Transmission When Road Surface Runoff Passing Beijing

In recent years, a growing number of environmental issues gradually grab public’s attention with the development of urbanization, among which urban water environment has seriously affected people’s daily lives. By making full use of the drainage system, taking biological measures to conserve water, and implementing the best measures to manage urban storm water, we can not only mitigate the influence of urban flood disasters and meet the urban water demand, but also improve the urban water environment as well as increase ecological benefits. To solve the problem of urban storm water management, on the basis of constructing grass swale, this thesis conducts road runoff test, water quality control test and employs SWMM model for simulated analysis to examine what role the grass swale play in the storm water management.This thesis mainly includes three aspects:(1) Research on how grass swale control road surface runoff. The research incorporates purification capacity tests, water regulation and storage tests, and physical properties of the filler comparative tests to provide theoretical guidance for the application of grass swale.(2) Simulated analysis of regulating effects of grass swale by applying SWMM model. The analysis includes sensitivity analysis of model parameters and the effect of regulation&storage with different grass swale coefficient, aiming to provide scientific basis for stimulating and constructing grass swale with application of SWMM model.(3) Evaluation on grass swale’s hydraulic loading capacity and economic performance. By exploring grass swale maintenance and management as well as economic evaluation, the thesis tries to provide guidance for engineering application of grass swale. Main findings of this paper are as follows:①Grass swale can be utilized to delay runoff producing and conserve groundwater. The established grass swale system in the test has longer runoff time than the asphalt road by10-15mins. In the case where grass swale with10cm hight outlet than no height outlet, it can process approximate1.5m3of water in an hour. The shorter the rainfall duration and the lower the intensity of rainfall is, the better regulation&storage results grass swale can produce. Compared with rainfall duration, rainfall intensity has greater impact on the infiltration capacity of grass swale. When the vegetation coverage is80%vs.20%, the grass swale can better control water volume, with the reappearance of scenario where annual rainfall infiltration capacity of0.33a1h is improved by8%.②Sand, gravel, perlite, peat soil, vermiculite, cinder, slag, zeolite and ceramsite, all of their porosity, saturation infiltration rate, permeability coefficient of the mentioned substance are greater than backfill, therefore their permeability performance are superior than backfill, and they can be used as substitute for backfill to fill the grass swale.③The grass swale established in the test have ammonia removal rate of10%-20%, total phosphorus removal rate of15%-35%, and COD removal of about20%. Besides greater rainfall intensity would reduce the swale purifying effect, while more vegetation coverage can improve the swale’s removal efficiency.④In the SWMM model building, the simulated results using the measured parameters are better than that of parameter values recommended in the manual. Nash-Sutcliffe efficiency coefficient and B%MSSE index calculated by the model using measured parameters were0.974,0.015, whereas results of the parameter values obtained from the manual were0.682,0.173.⑤Among MaxRate, MinRate, Decav, Surface Roughnes, the maximum infiltration rate of soil was sensitive parameters; the surface roughness was not sensitive while the sensitiveness of other parameters was medium. But the sensitivity of model parameters related to soil infiltration is also affected by rainfall intensity.⑥The simulated results of SWMM model demonstrate:the augment of grass swale storage depth will increase the amount of grass swale infiltration and delay the runoff producing; the higher the soil permeability coefficient is, the greater the amount of grass swale infiltration will be; the raise of longitudinal grade of grass swale will reduce the grass swale infiltration of water.⑦The regulation and storage effect is not obvious confronting with more than5a larger rainfall, and when the catchment area is large the effect is not conspicuous neither. The grass swale by size of50m2established in the test theoretically can completely infiltrate a road of50m2in1a with rainfall lasting24h according to the hydraulic load calculations. In addition, with the same area, the economic performance of grass swale is superior to sewer, porous roads, wetlands and wet retention pond.