Research On Runoff Pollution Characteristic Of Initial Rainwater In Nanning

With the advancement of urbanization,the impermeable surface area increased quickly,large amounts of pollutants carried by the rainwater runoff was produced by the rain washing the road.Some of the untreated rainwater runoff directly discharged into the receiving waters which seriously damaged the ecological environment,the others discharged into the city pipe network increasing the processing load of the existing measures.Rainwater runoff was one of the main factors which led to water pollution.The rainwater runoff was serious especially for the initial rainwater which had an obvious regional characteristic.Researched on the initial rainwater runoff pollution characteristics in different regions was significantly important for reduction of the urban rainwater runoff pollution.Based on the typical southern subtropical city Nanning,in this paper,we choose 6 sites in different functional areas in Nanning city,collected 8 rainfall events to exploring the pollution characteristics and regularity of the urban initial rainwater runoff,researching the distribution and first flush effect of that,.and suggesting the pollution control measures of initial rainwater.The main research content is as follows:(1)Selected eight representative rainfall events,and analyzed the distribution of pollutants' instantaneous concentration of the planed and built area in Nanning,the effected showed that:in all the 8 representative rainfalls,the surface runoff in built up area of NH3-N,TN,TP,COD and SS in average respectively,1.85?2.76,2.26?3.23,0.16?0.38,44.01?102.64,144.20?535.55 mg/L,and the planning area of the surface runoff were 1.33?1.60,1.71?1.93,0.20?0.21,50.24?51.63,144.35?164.39 mg/L,and the built up area pollution levels significantly higher than that of planning,business district is particularly serious,the early rain pollution index has more than the surface water environment quality standard(GB3838-2002)V class standard.(2)Analyzed the change of the rainwater runoff pollutants with the duration and the correlation between of them in four different rainfall patterns(light rain,moderate rain,heavy rain and storm),we found that:different pollutants under over time distribution was different.In light rain,the decline of pollutants was not obvious even had the rebound phenomenon,and in the moderate rain,heavy rain and storm are presented obvious downward trend.Under the condition of the heavy rain,the instantaneous concentration of pollutants within 5 minute can reduce 50%;70%-80%of the pollutants within 15 minute or straight line or into the city pipe network with rain.In all sampling points,the five pollutants of the built area had a different correlation,the NH3-N and SS show significant correlation(P<0.01).The five indicators of the planed area all showed the significant positive correlation(P<0.05).(3)Divided the sampling points into the five functional partition,described the strength of the initial rainwater first flush effect(FFE)in the various zones through the curve and the migration of the pollutants balanced line,the result indicated that:the FFE had a positive correlation with the rain intensity,the stronger of rain intensity the more significant of FFE,the sunny days were too long or too small,the effect would be not obvious;The flush curve of 5 function zones was above the 45° diagonal which in the curve of dimensionless cumulative load distribution,which explained that each function had obvious FFE.(4)Combined with,the distribution laws of pollutant concentration characteristics of initial rainwater and the analysis results of FFE,proposed a technical route,which combined the source retention,the process deceleration and the end adaption,to promote the management of Nanning's rainwater and optimize the drainage system.Provided a feasible management measures for the initial rainwater runoff pollution control and the construction of sponge city in Nanning.