| With the rapid development of China's economy and the acceleration of urbanization,the impervious foundation of the surface has increased,and the area of natural water such as green space and wetland has been decreasing,which leads to the decline of the infiltration and storage performance of rainwater runoff in cities.The phenomenon of "land watching the sea" can be seen everywhere after rainstorms.Therefore,according to the concept of sponge city.This paper takes the fourth sewage treatment plant in Lanzhou New District as an example,and combines the actual situation of the plant area to construct the ecological rainwater system,in order to provide some guidance for the construction of ecological rainwater system in Lanzhou New District.Firstly,in view of the engineering location and geological condition of the fourth sewage treatment plant in Lanzhou New Area,this paper mainly analyses the rainfall law,infiltration coefficient and collapsibility of the plant area,obtains the collapsibility grade of the plant area,and puts forward the protection points and solutions for the construction of ecological rainwater system in the area in view of its unique geological conditions.Secondly,several typical rainfall events in 2018 were collected,and the characteristics of pollutants in rainwater runoff of different underlying surface types were analyzed.On this basis,the interception of rainwater runoff by pavement pavement,low elevation greenbelt and bioretention ponds and the purification effect of water quality were analyzedthrough experiments and calculations.Finally,the planned ecological rainwater system is modeled by SWMM model,to analyze the feasibility of ecological rainwater construction in Lanzhou New District.Through the above research,this paper mainly draws the following conclusions:(1)The annual average rainfall of the four sewage treatment plants in Lanzhou New District is 244.08 mm,and the average stable infiltration rate of the plant ground was 9.47mm/h.The silt layer(1)of the whole plant has collapsibility,and the collapsibility coefficient is between 0.04 and 0.153.It is calculated to belong to the second-class self-collapsibility,and the degree of collapsibility is medium.The maximum impact depth of rainfall on the roadbed is about 1.5m.(2)The pollutants in rainwater runoff of asphalt concrete pavement,asphalt felt roof and bare road surface decrease with the increase of rainfall duration,and eventually tend to be stable.The correlation between SS and COD,TN and TP in asphalt concrete pavement is the highest,followed by roof rainwater asphalt felt runoff and bare road surface.The average pollutant concentration of each pollutant in rainwater runoff is only TP,which meets the surface water V-Class standard,while the rest do not meet the surface water V-Class standard,Rainwater runoff water quality is poor.(3)Experiments on reducing pollutants and runoff of rainwater runoff through permeable pavement,low elevation greenbelt and bioretention ponds and calculation of water balance,the efficiency of regulating and storing rainwater runoff and purifying rainwater runoff is analyzed.The results show that the permeability of sand-based brick is better than that of composite brick and ordinary concrete brick.Pervious brick has obvious effect on reducing rainwater runoff,but not very good effect on water purification.From the experiment of low elevation greenbelt,it is found that the removal effect of rainwater runoff pollution in concave green space with planting layer thickness of 500 mm is better than that of planting layer thickness of 200 mm and 300 mm.With the increase of concave depth,the seepage efficiency of rainwater runoff increases gradually,but at the same time,the ratio of service area to green area also has a great influence on the seepage effect.When the concave depth is 200 mm and the ratio of service area to green area is 10,the seepage rate of rainwater runoff in 10-year recurrence period is only 65.7%.The removal rates of SS,COD,TN and TP in bioretention ponds were all over 48.28%,which was better than that of permeable pavement an low elevation greenbelt.(4)The runoff coefficient method was used to check the hydrological parameters of the SWMM model established in the Lanzhou New District Fourth Sewage Treatment Plant.Rainfall data of 1-year and 10-year recurrence periods were taken into the model to verify the model.The runoff coefficients of the plant area were 0.411 and 0.553,which met the standard requirements.Using the experimental effluent of bioretention ponds as the index to compare the corresponding data in the model to judge whether the water quality parameters are reasonable or not.The results show that the relative error of each pollutant is less than 20%,and the water quality parameters also meet the requirements of modeling.(5)Using the calibrated model to simulate the ecological rainwater system in the Lanzhou New District Fourth Sewage Treatment Plant.The results show that compared with the traditional rainwater pipe network system,the ecological rainwater system has reduced the peak flow of rainwater runoff by more than 76.31% and the runoff duration by a minimum of12 min during the 10-year return period.The maximum runoff coefficient in the plant is only0.125.In addition,the ecological rainwater system has good removal effects on SS,COD,TN and TP,which proves that the construction of ecological rainwater system in Lanzhou New Area Fourth Wastewater Treatment Plant is completely feasible... |
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