Research On Characteristics Of Rainfall And Green Land Runoff Simulation In Hefei

Under the background of global climate warming and the accelerating urbanization process, the characteristics of rainfall change is one of the most obvious indicators of global climate change. It impacts on social and economic activities of human beings directly, which also limits the development of society. With the rapid development of China’s urbanization process, urban natural presence changes a lot, impervious area is greatly increased and the green area is shrinking, which leads to the low utilization of urban rainwater、the lower level of underground water and the decrease of water resource. At the same time, it has taken place great changes in city underlying surface runoff characteristics, the flood formation process is accelerated, the actual rain is on the rise, it has a serious impact on urban residents’ life and safety. Based on the topic of the city drainage pipeline system performance diagnosis and the evaluation system of research, the natural science research project in colleges and universities in Anhui province in 2011, choose Hefei as the object to study the city rainfall characteristics analysis and green land runoff characteristic, which provides design parameters and oretical reference for the design of the urban drainage pipe network, the urban water logging control research, plan and design of Hefei.In this paper, use the national weather service in Hefei weather stations on the basis of rainfall data from 1954 to 2013, use the Mann- Kendall test, Matlab language program to analyze rainfall trend and mutation features of the nearly 60 years, season and month rainfall. For nearly 60 years, the changes of annual rainfall is intense in Hefei, rainfall mutations are frequent, it has taken palce five times mutations between statistical, the overall annual rainfall present a rising trend; Spring rainfall presents a downward trend, Summer and Winter presents obvious rise, the rising trend of Fall rainfall is not obvious; The rainfall statistics of 6,9,10 month is the most dramatic change in the 12 months.According to the monthly rainfall change characteristics of Hefei, select characteristic month July rainfall data, to understand the distribution of rainfall patterns in Hefei and determine the rainfall simulation rainfall pattern. Design a artificial simulation of rainfall device, and to rate constant of the device parameters, on this basis, for more than 60 rainfall simulation experiments, analysis the influence of rainfall intensity, underlying surface slope, rainfall duration and initial soil water content to the green land runoff, the impact of these factors on the green land runoff coefficient and correlation. At the same time, the mathematical relationship of rainfall intensity and rainfall the mathematical with the runoff coefficient was established under certain conditions.The results showed that, the greater the rainfall intensity, the more obvious of the impact on storm runoff, the confluence at the mouth of the flow increase faster, the shorter the time to achieve stable production flow; Under the condition of same rainfall intensity, the green space to achieve stable production flow of time is longer than the expansive soil, and the convergence of green space of time than of the confluence of expansive soil; With the increase of slope, green land runoff coefficient increases, because of the green space intercept and disturbance of the rain, the green land on the surface of the water catchment time increased, the increase of runoff velocity slower than expansive soil conditions, stability of flow rate is also reduced; Rainfall intensity and runoff coefficient did not show obvious linear relationship; Green land runoff coefficient with rainfall duration have present a specific relationship, With the increase of rainfall, runoff coefficient increased, but in the end, the runoff coefficient is a stable value; It has present a linear correlation between rainfall and runoff coefficient, with the increase of rainfall, the runoff coefficient also increased. Compared with the runoff coefficient of the storm sewer design, the item 3.2.3 of outdoor drainage design specifications “GB50014-2006 " which provide the provisions of green runoff coefficient between 0.10 and 0.20, In Hefei Binhu new area green space of the runoff coefficient which between 0.15 ~ 0.3 is larger, In the actual project, we should adjust measures to local conditions to choose the right runoff coefficient.