Research On The Application Of SWMM Model In Sponge City

As urbanization continues to advance,the impermeability of the urban sub-base increases,causing dramatic changes to the original natural hydrological cycle system.The infiltration volume is significantly reduced after rainfall,which leads to a large amount of rainwater runoff pooling and discharging in a short period of time,putting great pressure on the urban drainage system.In addition,the surface source pollution load carried by stormwater runoff also makes the water quality condition of the receiving water bodies deteriorate sharply.Therefore,in order to solve the comprehensive water problems under urbanization,a new model of urban construction and development,"sponge city",which takes the total amount of urban runoff and pollution load as the control index,has emerged.This paper explores and analyzes the effectiveness of sponge by constructing SWMM models for two different spatial scales of typical plots and pilot areas,and using a combination of monitoring and simulation methods to study the pilot sponge city area in Fengxi New City.The runoff control rate and pollutant load reduction rate are used as evaluation indexes to compare and analyze the effects of rainfall runoff control and pollution load reduction at two different spatial scales before and after the construction of sponge city,so as to assess whether the sponge effectiveness is feasible at different spatial scales.The effect of different rainfall characteristics on the runoff control rate and pollution load reduction rate of sponge cities is studied by means of a long time series of rainfall throughout the year and a typical single rainfall,and the causes of the effect are analyzed.The key findings of this paper are as follows.(1)The effects of sponge facility construction on drainage capacity and pollution reduction in the study area were analyzed at two different spatial scales: typical plots and pilot areas.The results show that under different rainfall conditions,the overall runoff control rate and pollution load reduction rate decrease with the increase of rainfall,and these two evaluation indicators and rainfall are negatively correlated.The rainfall runoff control rate and pollutant load reduction rate in the study area are both greater after the construction of sponge facilities than before construction,indicating that the construction of sponge facilities has a better effect on the regulation of rainfall runoff and nonpoint source pollution load,and the sponge is effective.(2)By comparing the sponge effect at different spatial scales under the same rainfall conditions,it is found that the annual runoff control rate tends to increase gradually with the increase of spatial scale,while the pollutant load reduction rate shows a decreasing trend.And by studying the differences of sponge effects at different spatial scales,it was found that the spatial coupling of different spatial scales under the same rainfall conditions would have important effects on the runoff control rate and pollutant load reduction rate.The study of runoff control and pollutant load reduction patterns at different spatial scales reveals that there is a synergistic relationship between them.(3)Quantitative analysis of long time series rainfall by SWMM model reveals that the annual runoff control rate and annual pollutant load reduction rate of sponge cities have significant interannual variation patterns with the increase of rainfall in the last five years.Firstly,through the study of annual long time series rainfall,it was found that the higher the proportion of annual heavy rainstorms,the lower the control rate of runoff water quality;secondly,through the study of the influence law of rainfall intensity and rainfall ephemeris on runoff control and pollution load reduction under single rainfall,it was shown that several rainfall characteristics such as rainfall volume,rainfall intensity,rainfall ephemeris,and the proportion of annual ephemeris of heavy and heavy rainstorms would synergistically affect the sponge effectiveness.