The Study Of Runoff Control Based On Enhanced Infiltration

Enhancing infiltration is one of the technical measures for the construction of sponge cities.Using urban green land to infiltrate rainwater can reduce groundwater runoff and pollutants while reducing runoff.However,due to the inaccurate calculation of the infiltration volume and runoff for each rainfall event,it may cause waterlogging or increase the burden on infrastructure;at the same time,if the infiltration is continued for a long time,pollutants will pass through the soil layer and pollute the groundwater.In this paper,through analysis and reference of domestic and foreign methods and experience in rainwater management and runoff pollution control,combined with the local underlying surface conditions in Xi'an,this paper studies the rainfall infiltration of rainwater in Xi'an urban area.Through field measurement and software simulation,the infiltration and runoff conditions in the permeable area of Xi'an area under various conditions were analyzed,and the migration and control of runoff pollution in the soil were preliminary studied.The results show that:(1)The soil infiltration rate is mainly affected by the particle size distribution and bulk density of the soil: the larger the proportion of large particle size in the particle size distribution,the faster the infiltration rate;the lower the soil bulk density,The slower the rate of infiltration.According to the soil conditions in Xi'an,a new runoff calculation model is proposed,that is,the impervious area is calculated according to the runoff coefficient method,while for the permeable pavement,on the basis of clear runoff formation conditions,heavy rain,heavy rain,and heavy rain are given respectively The runoff coefficients under the conditions are 0.15,0.57,0.72.Instead of using the simple calculation method of 0.15,the corresponding runoff coefficients for different slopes,different rain peak positions and different rainfall intervals are given.(2)The water content of the soil and the changes of typical pollutants in the soil were measured by a fixed-head water injection test.The results showed that the concentrations of soil ammonia nitrogen,total nitrogen,and total phosphorus at the depth of 0-50 cm all increased to varying degrees;The migration speed in the depth direction is ammonia nitrogen> total phosphorus> total nitrogen;on the tenth day,the concentrations of ammonia nitrogen,total nitrogen,and total phosphorus in the soil were 4.1 times,2.9 times,and 1.4 times the base value,respectively.(3)Regulate the migration of water and pollutants by improving the soil at a depth of 5 cm(with 25% biochar added).The results show that the migration speed of pollutants and water is slowed and the content of pollutants and water is reduced.Among them,the removal rate of ammonia nitrogen,total nitrogen and total phosphorus in the improved soil layer at 5 cm depth was 67.8%,70.3% and 15.3%,respectively.By studying the migration of runoff pollutants in the horizontal direction,it was found that after soil improvement,the migration rate of water and pollutants slowed significantly and the radius of influence became smaller.(4)The seepage capacity of the seepage well has a positive correlation with its depth and radius,and the infiltration capacity of each size seepage well is given through simulation.When the seepage well penetrates into the runoff rainwater,the total phosphorus,total nitrogen,and ammonia nitrogen in the rainwater reach a depth of 1m in 20,28,and 12 hours;the concentration of each pollutant at a depth of 40 cm at 20 days accounts for 6.7%,6.25%,13%;seepage wells can reduce the concentration of pollutants infiltrating into the soil by improving the surface soil;(5)Under simulated continuous rainfall conditions,the concentration of soil pollutants in the green space along the road will continue to increase.The surface soil concentrations of ammonia nitrogen,total nitrogen,and total phosphorus at the end of the rainfall are 0.0037 mg / cm3 and 3.6mg /,respectively.cm3,0.93 mg / cm3.