Study On The Influence Factors Of Runoff Reduction For Urban Impermeable Underlying Surface Under Simulated Rainfall Condition

Urban permeable underlying surface is an important form of stormwater runoffdetention and absorption, which can relieve urban waterlogging disasters effectively,and reduce the pressure on urban drainage network. Through simulating the process ofstormwater runoff reduction on site with urban permeable underlying surface, this studydiscussed the area ratio between urban impermeable underlying surface and permeableunderlying surface under different conditions, and analysised the influence factors onthe runoff reduction process, to provide a scientific basis for the layout of the land forurban planning and rainwater utilization project design. According to the monthlyprecipitation data in1892-2010from Shapingba weather station in Chongqing, Thispaper analysised the precipitation characteristic annual and in flood season, using theartificial simulated rainfall device and typical urban underlying surface simulationdevice, through simulating the runoff-producing process of typical urban underlyingsurface, studied the curve of runoff under different rainfall and slope conditions,obtained corresponding runoff characteristic values, and on this base, simulated theprocess of runoff reduction of urban impermeable underlying surface flowing throughpermeable underlying surface, discussed the area ratio between impermeable andpermeable underlying surface under different rainfall and slope conditions, analyzed thesingle and multi-factors impact law on runoff reduction of impermeable underlyingsurface. The main conclusions of this study are as follows:(1) Under the vested conditions of the experiment, the critical area ratio betweenimpermeable and permeable underlying surface under dispersed water inlet mode andcentralized water inlet mode are5:1and4:1respectively. The area ratio has a negativecorrelation with the runoff reduction effects of the impermeable underlying surface withpermeable underlying surface, the runoff reduction effects under dispersed water inletmode is higher than the centralized water inlet mode under the same area ratio anddifferent water inlet mode. When the rainfall conditions and slope of permeableunderlying surface remain unchanged, the effect order of the two factors on runoffreduction effects is in sequence of area ratio＞water inlet mode.(2) The rainfall intensity has a negative correlation with the critical area ratio undertwo water inlet mode, the critical area ratio under dispersed water inlet mode are insequence of6:1(i=0.60mm/min)=6:1(i=1.07mm/min)＞5:1(i=1.43mm/min)＞ 4:1(i=1.92mm/min), the critical area ratio under centralized water inlet mode are insequence of5:1(i=0.60mm/min)=5:1(i=1.07mm/min)＞4:1(i=1.43mm/min)＞3:1(i=1.92mm/min). The runoff reduction effects under dispersed water inlet mode ishigher than the centralized water inlet mode under the same area ratio and differentrainfall conditions. When the slope of the permeable underlying surface is certain, theeffect order of the three factors on runoff reduction effects is in sequence of rainfallconditions＞area ratio＞water inlet mode, among them rainfall conditions and area ratiohave a negative correlation while water inlet mode has a positive correlation with runoffreduction rate of impermeable underlying surface.(3) The impact of the permeable underlying surface slope on the critical area ratiounder two different water inlet mode has a certain boundary law, it is shown as: whenthe slope is less than15°, the critical area ratio under dispersed water inlet mode are insequence of5:1(5°)-4:1(15°), the critical area ratio under centralized water inlet modeare in sequence of4:1(5°)-3:1(15°), when the slope is greater than15°, the critical arearatio under dispersed water inlet mode are in sequence of4:1(15°)-5:1(30°), the criticalarea ratio under centralized water inlet mode are in sequence of3:1(15°)-4:1(30°). Therunoff reduction effects under dispersed water inlet mode is higher than the centralizedwater inlet mode under the same area ratio and different slope. When the rainfallcondition is certain, the effect order of the three factors on runoff reduction effects is insequence of slope＞area ratio＞water inlet mode, among them slope and area ratio havea negative correlation while water inlet mode has a positive correlation with runoffreduction rate of impermeable underlying surface.