Research On Design Scale Of Typical Source Volume Control Facilities Based On Stormwater Runoff Pollution Reduction

With the gradual solution of the problem of urban point source pollution,the proportion of urban non-point source pollution is gradually increasing.The existing monitoring studies in many cities show that the pollution load of stormwater runoff usually accounts for more than 30% of the total load of urban water pollution,and a single separate drainage system can not completely solve the problem of urban stormwater runoff pollution.The accumulation of pollutants in rain water runoff usually goes through three stages: wet deposition,surface runoff and pipeline runoff.The characteristics of pollutant concentration change in each accumulation stage are different.The first flush effect is obvious in the first stage and the second stage,while the pipeline system in the third stage will weaken the first flush effect of runoff.Theoretically,the source control facilities can achieve better pollutant control effect.At present,the domestic research on urban stormwater runoff pollution control mainly focuses on a single technical measure or a single project,and most of them are single rainfall research,lacking the research on the annual reduction effect of stormwater runoff pollution under various facilities and scenarios with annual total runoff control rate as the core.Through the SWMM model of rainstorm and flood management,large and small-scale regional models are established.Through weir,orifice,pump and control editor module,terminal volume control facilities which can be used for field and multi-year simulation are built.Referring to the cumulative load volume fraction curve(M(V)curve),the concept of load control rate volume control rate ratio(MV control ratio)is proposed to deal with the field simulation results.Combined with the simulation results for many years,the source and end volume control facilities with different design scales are studied,which can change the rainfall return period,rainfall duration and rainfall drop The main conclusions are as follows:(1)In different scenarios,the pollutant control effect of source facilities is better than that of end facilities of the same scale in most cases.The pollutant control effect of terminal volume control facilities will be weakened by the change of drainage area scale from small to large and the uneven spatial and temporal distribution of regional rainfall.The pollutant control effect of infiltration source facilities is more sensitive to the change of rainfall return period,while that of storage terminal facilities is more sensitive to the change of rainfall duration.The pollution control rate of source facilities and end facilities increased with the increase of the proportion of green space or road area in drainage area,and the pollution control rate increased significantly with the increase of the proportion of green space.(2)Under the condition that the total facility scale remains unchanged,the combination of source volume control facilities will not enhance the overall pollutant control effect of the project,and its overall pollutant control effect is between the best and the worst.The overall facility scale remains unchanged,When the floor area of infiltration facilities increases due to the change of facility structure layer,the runoff control and pollutant control effect of the facility will increase with the increase of the floor area within a certain range.The overall facility scale remains unchanged,When the source volume control facility is insufficient and the end volume control facility is used to supplement,the pollutant control effect of combining the source and end facilities is significantly better than that of using the end volume control measures alone,and slightly worse than that of using the source volume control measures alone.(3)From the point of view of volume control,when the stormwater bucket or storage tank is designed dynamically according to the rule of starting drainage after 24 h and emptying within 24 h after rain,a better effect of annual stormwater runoff pollution reduction can be obtained.However,if the drainage is not started more than48 h after the rain,the annual runoff volume reduction rate of the storage facilities will be sharply reduced,and the pollutant control effect will decline in a fault way.(4)For example,the stormwater control facilities are arranged according to the overall design scale of N% annual total runoff control rate in a diversion production area(60 ≤ n ≤ 90),and the end volume control by using the stormwater treatment plant(including the reservoir)alone can achieve an annual average of N% ± 5%reduction rate of stormwater runoff pollution;Using stormwater bucket alone to control the source volume can achieve an annual reduction rate of N%-5%;The end volume control by using the end closure storage tank alone can achieve N%-5% ～ 10% annual runoff pollution reduction rate;Combined with the use of facilities with infiltration structure such as biological detention tank and permeable pavement for source volume control,the annual average N% + 10% ～ 20% reduction rate of stormwater runoff pollution can be achieved;Combined with the source + end control method,the annual runoff pollution reduction rate of N% + 5% ～ 10% can be achieved.