Control Of Typical LID Measures For Urban Non-point Source Pollution

The rapid development of urbanization aggravates the problem of urban non-point source pollution.Lid measures are widely used in non-point source pollution control at present.In this thesis,a residential area of Jinzhou District in Tianjin was taken as a research area and combing with its planning scheme,the physical experiments of four typical LID measures,including permeable pavement,sunken greenbelt,vegetative swale and bio-retention cell,are conducted.A numerical model of non-point source pollution was established to simulate the control effect of LID measures under different LID setting schemes,different rainfall repeat-periods and different rainfall durations.The main research contents and achievements are as follows:（1）The pollutant index of physical model experiment and the type of typical LID measures were determined according to the low impact development plan of the research area and relevant researches.In this thesis,five common non-point source pollutants--SS,COD,TN,TP and NH₃-N--were taken into consideration,and the methods to determine their concentrations are proposed,respectively.The physical model experiment of four selected typical LID measures,including permeable pavement,sunken greenbelt,vegetative swale and bio-retention cell,were conducted,and the experimental devices and experimental scheme of each measure were designed.（2）The experimental results of physical model were summarized and the pollution reduction law of each LID measure were analyzed.The results show that the pollutant reduction effect of permeable brick pavement is better than grass-planting bricks.No significant positive correlation exists between the depth of the concave of sunken greenbelt and the pollutant reduction rate.The higher the slope of vegetative swale is,the greater the TN reduction rate is,while the reduction effect of vegetative swale with different slopes is similar for other pollutants.As a whole,the effect of fillers on pollutant control is as follows:the composite filler of furnace slag and sand>the composite filler of fly ash and sand>soil,but the TP reduction effect of soil is better than the composite filler of fly ash and sand.（3）The synthetic drainage system of the study area was generalized on the basis of the planning drawings.The numerical model of non-point source pollution of the study area was established and the parameters were verified with physical experiment results,the model manual and literature materials.Under the conventional development scheme,the comprehensive runoff coefficient of the model is within the empirical value range of urban comprehensive runoff coefficient.The relative error range of parameter calibration of permeable pavement,sunken greenbelt,vegetative swale and bio-retention cell is 0.58%～5.03%,-1.39%～0.70%,-2.65%～2.04%,-6.33%～4.95%The simulation results of water quality parameters of different land use types are within the reference value range,which shows that the model can reflect the hydrodynamic water quality characteristics of the study area.（4）The layout of different LID measures,rainfall repeat-period and rainfall durations were simulated through the non-point source pollution numerical model,and the control effect of LID measures was analyzed.The simulation results indicated that the combined LID measures have the best control effect on non-point source pollution,the larger the rainfall return period,the smaller the reduction rate of pollutants.With the increase of rainfall duration,the control effect on non-point source pollution of LID measures decreases,indicating that the LID measures have a better control effect on non-point source pollution in the short rainfall duration of low rainfall repeat-period.