Research On Source Control Technology Of Urban Rainstorm Waterlogging

The urbanization develops rapidly and water permeability of the layer under city ground. Influenced by the global climate change, the chances of waterlogging in the city under sudden rain would increase, and impact extent and range deepen increasingly then public facilities and people’s lives and properties are threatened. Runoff controlling from source is the most fundamental method to avoid urban rainstorm waterlogging. Therefore, proceeding from that fundamental issue, the research about source control technique of urban rainstorm waterlogging has not only the great scientific significations but also the practical application value.Based on the analysis of urban rainstorm waterlogging features, causes and factors, the waterlogging depth of the water by precipitation intensity, duration of rainfall, coefficient of permeability and impervious rate would be determined. By theoretical and model created by SWMM (Storm Water Management Model) analysis, rainwater depth could be calculated and low impact development measures, the poundage and its proportion of impounding reservoir and other related concepts are mentioned. Connecting the artificial rainfall test and computing theory of urban rainstorm waterlogging, and comparing the runoff situation of the study area with and without the LID technology. Effects of LID in rainstorm source controlling are investigated, and specific control technique would be determined. Main results of the study are followed:1. Using theoretical analysis and SWMM numerical modeling, the waterlogging depth of rainfall by different factors of precipitation intensity, coefficient of permeability and impervious rate could be calculated. The fitting formula is h=-0.33(1-r)k+Q.For a single event of rainfall, the most effective way to reduce depth of sub-catchments is increasing natural infiltration capacity of soil by using soil with higher coefficient and decreasing impervious rate of sub-catchments.Such as when the coefficient of permeability is 0%. impervious rate is 120.4mm/h compared to 0.254mm/h, in the face of 100 years recurrence period rainfall situation, the waterlogging depth of rainfall decreased by 35.866 mm. And when impervious rate is 76.2mm/h, the coefficient of permeability is 0% compared to 80%, in the face of rainfall reappearing period is 100 years, the waterlogging depth of rainfall decreased by 28.76 mm.2. Studied the storage coefficient p values, which is the design parameter of source control technique of urban rainstorm waterlogging.The storage coefficient p was determined which is a specific value between total storage volume Qc and original waterlogging volume Qj.The calculation formula is Qc=-0.33p(1-r)kA+ pQA. And values of the storage coefficient p has three cases:(1) coefficient of permeability and impervious rate are the quantitative, rainfall reappearing period is variable; (2) rainfall reappearing period and impervious rate are the quantitative, coefficient of permeability is variable; (3) coefficient of permeability and rainfall reappearing period are the quantitative, impervious rate is variable. Such as when impervious rate is 76.2mm/h, the coefficient of permeability were 0%,20%,40%,60% 80%,100%, in the face of rainfall reappearing period is 100 years, the storage coefficient p respectively were 0.65,0.67,0.69,0.70,0.72,0.73, this moment the waterlogging depth of rainfall h’j down to 30 mm.3. Artificial rainfall test sduty about the influence of the waterlogging depth of the water by taking different hardening rate and storage measures.Two different cases of rainfall were modeled by artificial rainfall test. The uniformities of two cases are 0.981 and 0.967 respectively; mean values of rainfall are 109.66mm and 87.223mm, those values are corresponded to 100 years and 20 years recurrence period rainfall situations. Then the under layer with 4 different impervious rate values was modeled in this paper, and waterlogging depth, seepage situations under different conditions were monitored. In the same condition, depth of waterlogging increases with impervious rate value, the amplitude of 100 years is a little larger than the value of 20 years. The increasing tendency matched the formula of hardening model mentioned in Chapter 3. On the basis of impervious rate changing, impounding reservoir under low impact development measures was added at the same time. After measures taken, the depth of waterlogging reduced to a certain extent.4. The project research about source control technique of urban rainstorm waterlogging how to affect the waterlogging depth of the water.Region model was created using SWMM in this article, LID technique such as low elevation greenbelt, Bio-Retention Cell and permeable pavement was selected to attach to the original model, runoff coefficient decrease from 0.669 to 0.298, volume capture ratio of rainfall could up to 70.2%. The results of the numerical analysis presented that LID technology played an efficient role in decreasing runoff peak velocity and node flooding velocity, reducing flooded hours and total flood volume.