Simulation And Parameter Impact Analysis Of Infiltration Process In A Sponge City

Studying the infiltration process of sponge cities helps to reveal their runoff mechanism and provide hydrological basis for rainstorm simulation and control.This article takes the Weihe River No.8 system zone(WR8)in the pilot area of Fengxi sponge city as the research object,uses the Storm Water Management Model(SWMM)calculation engine run by Visual Studio 2022,and analyzes the impact of the parameters of design rainstorm and Horton infiltration equation on SWMM simulation infiltration process.The main research results are as follows:(1)Analyze the SWMM operation code and summarize its infiltration calculation principle and process:First,calculate the infiltration rate and time-period infiltration volume process of each sub-catchment’s pervious zone and low-impact development(LID)facility zone separately;secondly,calculate the sub-catchment infiltration rate(the area-weighted average of infiltration zone and LID facility zone infiltration rate)and time-period infiltration volume(the sum of timeperiod infiltration volume of infiltration zone and LID facility);finally,calculate the study area infiltration rate(the area-weighted average of each sub-catchment’s infiltration rate)and timeperiod infiltration volume process(the sum of each sub-catchment’s time-period infiltration volume).At the same time,in a certain sub-catchment,if the ratio of the permeable pavement zone to the sub-catchment increases by n,then the ratio of the pervious zone,non-depression impervious zone,and depression impervious zone to the sub-catchment will decrease by 0.24n,0.19n,and 0.57n respectively.(2)Under uniform design rainfall and Chicago design rainfall,the larger the rainfall return period,the infiltration rate(including initial value and peak value)and time-period infiltration volume of pervious zone,permeable pavement zone,sub-catchment and WR8 all increase;under the same Chicago design rainfall,the infiltration rate is equal to the corresponding rainfall intensity before reaching its peak value,and after reaching its peak value it decreases in accordance with the downward trend of the infiltration capacity curve.(3)Under Chicago design rainfall,the later the peak of the rainfall,the smaller the peak value and the later the peak time of infiltration rate and time-period infiltration volume of pervious zone,permeable pavement(PP)zone,sub-catchment and WR8.For example,under Chicago design rainfall with a recurrence period of 5 years and rainfall peak position coefficients of 0.2,0.4 and 0.6,the peak values of infiltration rate in pervious zone are 0.2593,0.1974 and 0.1575 mm/min respectively,and the peak values of time-period infiltration volume are 10.67,8.12 and 6.52 m3 respectively.The peak times of infiltration rate and time-period infiltration volume in pervious zone are 18,30 and 39 min respectively,while those in PP zone,subcatchment s7 and WR8 are all 24,48 and 72 min respectively.(4)Under Chicago design rainfall,with respect to the peak value and peak time of infiltration rate and time-period infiltration volume in pervious zone,they are positively correlated with initial infiltration rate(f0),not(weakly)correlated with stable infiltration rate(f∞),and negatively correlated with decay coefficient {kd);when f0,f∞ and kd all increase,or when f0 and f∞ increase and kd decreases,or when f0 and kd increase and f∞ decreases,both the peak value and peak time of the two increase;when f∞ and kd increase and f0 decreases,both the peak value and peak time of the two decrease.(5)Under Chicago design rainfall,with respect to the total infiltration volume in pervious zone,it is positively correlated with f0 and f∞,and negatively correlated with kd;when f0,f∞ and kd all increase,or when f0 and f∞ increase and kd decreases,this value increases;when f0 and kd increase and f∞ decreases,this value decreases;when f0 decreases,and f∞ and kd increase,this value first decreases then increases.