Calculation Method Of Urban Rainfall Runoff Non-point Source Pollution And Its Application

With the rapid economic development,the urbanization process has accelerated,the problem of urban water pollution is becoming more and more serious,and it has seriously affected the sustainable development of cities.The non-point source pollution of rainfall and runoff is an important source of urban water pollution.In this paper,the calculation method of urban rainfall runoff non-point source pollution is studied.And based on the distributed SCS hydrological model,a distributed urban rainfall runoff non-point source pollution model is established in the Wuhan South Lake Basin.Provides technical basis for urban water pollution control through quantitative calculation of rainfall-runoff non-point source pollution load.The main research results of the paper are as follows:（1）Analyze the limitations and characteristics of the current calculation methods for rainfall and runoff non-point source pollution load,and focus on the calculation method of non-point source pollution load based on distributed SCS hydrological model.The model parameters are simple and can fully consider the impact of the underlying surface on runoff.It is suitable for the simulation calculation of rainfall and runoff in urban small watersheds.Analyze the influence of the initial loss coefficient of model parameters.The results show that under different types of land use,different initial loss coefficients should be selected due to the different permeability of different pads to runoff.（2）Analyze the water quality of the Nanhu Lake Basin and evaluate that the lake is in a state of moderate eutrophication,and the water quality is in the inferior V category in the past 9 years.Analyze the annual and monthly changes of the main pollutants COD,NH₃-N,TP,TN,and combine the field survey data to determine that the main source of pollution is non-point source pollution.（3）Select different initial loss coefficients for different land use types,construct a distributed SCS hydrological model of the Nanhu Lake Basin.Apply the model to the calculation of rainfall runoff in the basin,and compare and verify its results using the measured lake volume change and runoff coefficient method.The results show that the improvement of the initial loss coefficient of the distributed SCS model in the South Lake Basin is reasonable,and it has a better simulation effect than the traditional runoff coefficient method.（4）Combined with the measured pollutant concentration data,the non-point source pollution load of rainfall and runoff in the South Lake Basin was calculated.The time distribution of pollution load and the impact of land use changes on it were analyzed.The results show that the non-point source pollution in the Nanhu Lake Basin is mainly concentrated from March to July,accounting for 64.36%of the year.In recent years,the urbanization process has led to an increase in the area of construction land,which has caused surface pollutants to flow directly into lakes without filtering,and non-point source pollution of rainfall and runoff has increased.