| In recent years, the city's capacity to retain rainwater reduced dramatically as the sharp increase in harden underlying surface. During the heavy rain, because of the reduction of infiltration rainwater, large runoff and poor drainage, floods occurred frequently in many cities. The state strongly promote the construction of sponge city which characterized by natural reservoir, natural infiltration, natural purification while carrying out the drains engineering system. As the terrain of the mountain city is hilly, the runoff generate rapidly which may result in great potential risk. So it has important significance for solving a waterlogging problem, building sponge city as well as utilizing rainfall flood resources to research the runoff process, conflux process and the runoff coefficient of the mountain city. This paper takes the grass, pervious brick ground, asphalt pavement of Chongqing Garden Expo Park as the research object. In this paper, the runoff generation as well as the conflux process on the different slope of underlying surface caused by different rainfall intensity has been studied by the method of rainfall simulation. Based on the experimental data, the functional relation of the runoff coefficient and influence factors is fitted. Research results and conclusions are the following:?The runoff generates in 5 to 10 minutes after the start of rainfall on the lawn. The greater the rainfall intensity, the earlier appear the runoff generation. The ERC changes from 0.098 to 0.169 when the slope is 8° and the rainfall intensity increases from 0.63mm/min to 1.62mm/min. On similar rainfall intensity, The ERC changes from 0.118 to 0.217 when the slope is 25°. On the same rainfall intensity, ERC increases as slope increases. The difference of ERC between the two slopes is 0.048 when the rainfall intensity is strong.?The runoff generates in 7 to 12 minutes after the start of rainfall on the pervious brick ground. IRC and ERC increase with the rainfall intensity. The ERC changes from 0.208 to 0.423 when the rainfall intensity changes from 0.68mm/min to 1.301mm/min.46 minutes after the runoff, the IRC increases significantly when the rainfall intensity is 0.68mm/min.?Rapid generation of runoff was shown on asphalt pavement in this study, and the runoff generated in the first or second minute of a rain. The rainfall intensity and slope have little impact on initial runoff generate time and IRC. And ERC increases slightly with the slope.? On lawn the relationship between IRC ?t and duration t can be expressed by these two fitting formulas:?t=a-be-ct and ?t=a-bt-0.5.IRC grows gradually after the generation of runoff,and the growth rate varies with t.It approaches to a if the t lasts long enough,and the ranges of parameter a in the two types of functions were 0.130 to 0.278 and 0.217 to 0.423.? The relationship between lawn's ERC ?c and rainfall intensity q can be expressed that ?c=1-a/q-b.The formula shows that IRC increases with q,and it approaches 1 when q is large enough. Linear fitting has been used between the slope i and ?c, and a general formula was obtained which was that ?c=ai+b.?c increases with i under the same intensity.? On asphalt pavement The relationship between IRC ?t and t can be expressed by the available function expression ?t=a-b/(t+c).When t is big enough, ?t approaches a,and a ranges from 0.933 to 0.998.The relationship between ERC and intensity q could be expressed by ?c=1-a/q-b. ?c and slope i are linear fitted, and ?c increases with i under the same rain intensity. |
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