Study On Rainfall Runoff Pollution Control On Campus Based On LID

With the acceleration of urbanization,a large number of naturally permeable underlying surfaces have been replaced by impervious surfaces,resulting huge changes in urban rainfall runoff characteristics compared with natural areas,including an increase in rainfall runoff rate and surface runoff,flood peak ahead of time and pollution increase,which have a great negative impact on control and prevention of urban flood,protection of water environment and utilization of water resources.Under this background,there is a hot topic that low impact on developing optimal control measures(LID-BMPs)of urban rainfall runoff in the world.The campus environment is one of the functional districts of the city.It has a high degree of similarity with the city.The naturally permeable underlying surface of the campus is replaced by the impervious underlying surface,replacing the original hydrological cycle and resulting in runoff pollution problems.Therefore,through the study of rainfall pollution on campus,it is also significant to develop low-impact design for the campus.In this paper,we selected a campus in Xiqing District of Tianjin as a research area,we collected and analyzed the rainfall runoff of four different underlying surfaces(green roof,road,concave green space and impervious paving)in five rains.The rainfall runoff pollution in the area is studied.Based on the basic data of the study area and the characteristics of rainfall runoff pollution,the objectives of rainfall runoff pollution control were determined,the appropriate LID-BMPs engineering measures were selected to plan the study area.SWMM model was used to simulate the hydrological and water quality of the study area before and after designing campus landscape and planning program was determined at last.The main results are as follows:1.The study area has gentle slope and no steep terrain.The soil type is loam,and the impervious area accounts for 71%.The rainy season mainly concentrates in 6,7 and 8 months.The existing LID engineering measures include rainwater garden,grass ditch,concave green space,water-permeable paving,green roof,etc.However,the coverage rate is low.Waterlogging phenomenon in campus has occurred in recent years,exerting great pressure on urban pipe.Therefore,it is necessary to develop low-impact design for the study area.2.According to the curves of runoff water pollutant concentrations with different runoff times,it can be seen that the concentrations of pollutants in the initial runoff are generally high.Under rainwater scour,the concentrations of rainwater pollutants in different types of underlying surface are generally decreased in the range of 5 min to 10 min,while the latter tended to be stable.Along with the sampling date,water quality indicators generally show a downward trend of different types of underlying surface.The Initial rainfall effect is obvious.3.In roof rainfall runoff,COD and TN are poor V class of surface water environmental quality standard and TP is III class;In impervious paving runoff,COD is poor V class of surface water environmental quality standard,TN and TP are respectively IV class and III class;All the water quality indicators of concave green space are poor V class of surface water environmental quality standards;In road rainfall runoff,COD and TN are poor V class of surface water environmental quality standards and TP is III class.In general,the concave green space is the most polluted,followed by roads and roofs,and finally is impermeable paving.The main reason for the analysis is that the concave green space can absorb part of the runoff pollutants by itself,but the water in the concave green space has been subjected to microbial fermentation for a long period of time resulting in the generation of pollutants.The road is subjected to many human factors.Because of the accumulation of the dust,the road is not easy to clean.On the roof,pollutants come from single source,mainly air dust or soil and fertilizers produced by planting plants involved in runoff.Impervious paving has less interference of human factors,and the material surface is relatively smooth,rainfall runoff easily washed surface dust.4.The inhomogeneity of rainfall intensity is an important factor that affects the fluctuation of pollutant concentration on each underlying surface.Road runoff pollutants are most affected by changesof rainfall intensity,especially rainfall runoff turbidity significantly increases at a time when rainfall intensity increases;In addition to conductivity,the other pollutants in roof rainfall runoff have fluctuations,but the overall have downward trend;Except conductivity and turbidity in impermeability paving runoff,there has a fluctuation of othe pollutants,but the overall has downward trend.The reason is that the rainwater scouring action is relatively large,and the surface runoff water quality concentration of each underlying surface gradually decreases under the scouring.While the road is uneven,when the rainfall intensity increases,the accumulated sediment is scourred and the turbidity increases.5.The roof rainfall runoff and rainfall intensity change are positively correlated,that is rainfall intensity changes with rainfall runoff.Analyzing the effect of rainfall runoff on roof runoff rainfall quality,the change of rainfall runoff also led to the fluctuation of pollutant concentration,but the pollutant concentration shows a downward trend as a whole,indicating that the effect of rainwater flushing is obvious.By calculating,the average runoff coefficient is respectively 0.85 and 0.91 under moderate rain and storm.6.From the correlation between runoff SS and COD,TN and TP in the same underlying surface,the correlation between SS,COD,TN and TP of roof,road and impermeable paving is significant,while the concave green space is not significant.From the correlation between runoff SS and COD,TN and TP of different underlying surface,the correlations between SS and COD,TN and TP of road is the best relative,then is roof and impervious paving,the last is concave green space.Except the concave green space,the correlations of SS and COD,TN and TP other three types of underlying surface are relatively.The reason is that this is related to surface runoff coefficient,and concave green space can can given some pollutants by itself.Reducing the SS concentration in the runoff can reduce the COD,TNand TP in the runoff.7.The study area is divided into 19 sub-catchment areas,designing two-year and five-year rainstorm models,and two typical sub-catchment areas(S8 and S15)are selected to be simulated by SWMM.According to conditions and relevant data of the research area,the control target of rainfall runoff pollution in the study area is determined.After constructing model and calibrating the parameters,the two sub-catchment areas were simulated under two different rainstorm models.The simulation results show that the total runoff of the two sub catchment areas decreased and the pollutant concentration decreased.The peak value reduces and the peak appears delayed.For the two storm models,the designs basically reach the control target.However,design efficiency is good in the heavy rain model of once in two years scenario.It has a higher reduction rate of total runoff and growth rate of total pollutant load than that of the once in five years scenario.