| Rapid urbanization had caused the rapid growth of the area of high-density building complexes,which had hindered the process of urban rainfall production and flow based on the natural water cycle.The ‘fast drainage’ model of the traditional drainage system had greatly shortened the surface confluence time and caused frequent urban waterlogging.With the promotion of Chinese sponge city construction and the international concept of combining urban rainwater management system with urban green space system,domestic scholars had gradually explored the construction model of sponge green space to reduce runoff,purify water quality from the source ecological purposes,which such as alleviating the pressure of pipe network drainage.In view of the above problems,this thesis focused on the two main lines of the impact of urban greenbelt soil physical properties and micro-geomorphology accumulation capacity on rainfall-runoff,and used the actual measurement of the physical properties of greenbelt soil in building and sub-district in Beijing,and established green land micro-geomorphology devices to discuss the correlation influence factors of soil penetrating quality of green land and corresponding soil permeability model,by using kinematical wave calculation model and SCS-CN model to comprehensively analyze the influence of soil quality of buildings and residential areas on runoff coefficient and the volume of infiltration and runoff.Based on Beijing common micro-geomorphology form of slope terrain and depression in the construction district of the city,this thesis investigated the impact of different rainfall conditions and changes of micro-geomorphology factors on the runoff time,storaged capacity and runoff coefficient of green space.This thesis could provide a methodology and theoretical reference for the scientific assessment of soil infiltration capacity and runoff coefficient of green space.The main conclusions of this thesis were as follows:(1)The soil permeability of the three functional areas within the scope of this thesis were as follows: residential area > cultural and educational area > commercial area.The measured infiltration curve was most in line with the Horton infiltration model.According to the measured data,the green space infiltration in the Beijing built-up area was obtained coefficients,initial moisture content,bulk density,density,pore ratio,vegetation coverage and human disturbance.Theoretical analysis showed that the void ratio,initial moisture content and initial infiltration rate of soil internal factors are closely related to each other,and the external factors are vegetation.The coverage was strongly negatively correlated with human disturbance.The initial infiltration rate could establish a preliminary linear relationship with the initial water content and vegetation coverage.The steady infiltration rate was mainly related to the initial infiltration rate and initial moisture content rate.(2)Using the kinematical wave calculation model and the SCS-CN model to calculate the greenbelt rainfall-runoff coefficient value table,compared with the empirical value method commonly used in engineering practice in China,the SCS-CN model was closer to the empirical value.This thesis refined the values of green space runoff coefficients under different greenbelt soil properties,vegetation coverage,and rainfall conditions.The resultsshowed that under the design rainfall conditions corresponding to the annual total runoff control rate of 75% to 85% in Beijing.The range of runoff coefficient was limited to 0 ~ 0.43.The runoff coefficient is influenced by the actual environmental factors such as soil texture,degree of moisture,green space rate,rainfall conditions,and was also restricted by the depth of the soil and the void ratio.(3)Under the same rainfall recurrence period and rain type conditions,the depression was lower,the grade was heavier,the runoff time was longer,infiltration volume and runoff coefficient was greater,and the peak runoff point was earlier,and vice versa;The same return period and terrain under the conditions,the runoff time and runoff coefficient under the Chicago rain pattern were greater than the test results under the even rain pattern;The green land rainfall runoff coefficient measured in this thesis ranged from 0.08 to 0.25.(4)Under different slopes,the green space runoff coefficient had a positive logarithmic relationship with the rainfall recurrence period,and a positive correlation with the binary function of rainfall.The relationship between the runoff coefficients obtained from rainfall has a high degree of fitting,and the calculation was simple;The green area runoff coefficient and the recurrence period had a positive correlation between power functions in different depressions.When slopes and depressions worked together,the uniform rain-type downslope had a significant effect on the peak runoff.If the number of depressions increased,the degree of impact weakens and the peak runoff point might be delayed.Under the Chicago rain pattern,the impact of depressions was more prominent. |
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