| Rapid urbanization has resulted in an increase in impervious areas and surface runoff,which has caused many urban water problems,such as waterlogging,water pollution and water shortage.For this reason,China vigorously promotes the construction of"Sponge City"with low impact development rainwater system construction as the core.However,different LID measures have different hydrological responses and water quality treatment characteristics,and the abilities of rainfall runoff control of LID measures are closely related to the local physical and geographical conditions.Further exploring and improving the LID technology system in combination with regional soil types and rainfall characteristics and other natural geographic characteristics will help to promote the sustainable development of"sponge city"construction and realize the localization and application of LID measures in China.Therefore,this study explored the changes of rainfall runoff water quality and quantity of LID measures such as sunken lawn,permeable pavement,green roofs,bioretention facility,and constructed wetland in Guangzhou city from the scales of pilot experiments,field experiments,and field monitoring.Based on the results of the previous part of this study,the effects of LID measures on the control of rainfall runoff in the lateritic red soil region of Guangzhou were systematically studied combined with the Hydrus-1D model and SWMM model.The main results of the study are as follows:(1)Pilot experiments devices of the sunken lawn,permeable pavement and green roofs were constructed,and the experimental study on the effects of LID measures on the control of rainfall runoff was carried out by artificially simulating rainfall runoff or rainfall.The results showed that the rainfall runoff volume reduction rate(R_V)and pollutant load removal rate(R_L)of the sunken lawn decreased as the rainfall recurrence period increased.The runoff volume reduction capacity of the different plants decreased as follows:Axonopus compressus>Zoysia matrella>Ophiopogon japonicas>bare soils and the rainfall runoff pollutants load removal ability of Axonopus compressus was the best.Besides,the R_V of permeable pavement decreased with the increase of rainfall intensity.The R_L of permeable pavement in light rain was higher than that in heavy rain.For green roofs,the R_V decreased with the increase of rainfall intensity.The ability of green roofs with different substrate layer thicknesses to reduce runoff volume decreased as follows:70mm>50mm>30mm.(2)The field experiments bioretention facilities were constructed to explore the effects of bioretention facilities on the control of rainfall runoff under different rainfall recurrence periods,biochar distributions,internal water storage(IWS)zone heights and exfiltration conditions,so as to assess the hydrologic performance and rainfall runoff pollutants removal capacity of bioretention in a lateritic red soil region.The results shown that incorporating biochar into the planting soil of the bioretention facilities can increase the water content raising capacity of the planting soil and improve the runoff pollutants removal capacity of the bioretention facilities.Overall,the runoff control capacity(i.e.the R_V and R_L)of different biochar distributions decreased as follows:biochar was uniformly mixed with the lateritic red soils>biochar was stratified with the lateritic red soils>biochar was excluded in the planting soil layer.The R_V,R_L(except COD)and the rainfall runoff concentration removal rate(R_C)(except COD)under different IWS zone heights were all decreased as follows:40cm>20cm>0cm.Meanwhile,the runoff control capacity of permeable bioretention was significantly higher than the impermeable bioretention;however,increasing the IWS zone height of the impermeable bioretention facility could reduce the gap between the two.(3)The permeable pavement,green land and constructed wetland in Guangzhou Tianhe Smart City were selected to carry out long-term on-site monitoring.The effects of rainfall runoff water quality control of permeable pavement and green land were analyzed,and the water quality changes of constructed wetland under different seasons and rainfall intensities were explored.The field monitoring data of permeable pavement,green land and constructed wetland were analyzed,and the results showed that the R_Vs of permeable pavement and green land tended to decrease with the increase of rainfall duration,rainfall accumulation and maximum rainfall intensity,while they tended to increase with the increase of the antecedent dry period(ADP).The ADP was longer would result in the more pollutants accumulated on the surface,and finally made the rainfall runoff pollutants concentration from permeable pavements and green land to be higher.The average comprehensive water quality identification index(CWQII)of different seasons were ranked as:winter(5.98)>spring(4.67)>autumn(4.66)>summer(4.26).Moreover,the ranking of the average CWQII of the constructed wetland under different rainfall intensities was:torrential rain(5.09)>heavy rain(4.88)>light rain(4.50)>no rain(4.39)>moderate rain(3.95).(4)The Hydrus-1D model of each LID measure was constructed based on the structural parameters of the devices and facilities and the properties of their fillers,and used the experimental observation data to calibrate and verify the model parameters,so as to explore the effects of a single LID measures on the control of rainfall runoff.The simulation results showed the catchment area ratios,aquifer layer heights and planting soil thicknesses of the impermeable bioretention facility had positive linear correlation with the R_Vs and R_Ls.However,it was a positive linear correlation between catchment area ratios and aquifer layer heights and the R_Vs of the permeable bioretention facility,while the relationship between the planting soil thicknesses and the R_Vs was negative.Besides,there was a positive linear correlation between the water catchment area ratios,gutter inlet heights,planting soil thicknesses and the R_Vs of sunken lawn.As for the permeable pavement,there was a positive linear correlation between rainfall duration and the R_Vs,and the relationship between rain peak coefficients and the R_Vs was a logarithmic function and negative correlation.And the permeable brick permeability coefficients and the R_Vs was a positive correlation.(5)The rainfall runoff volume and water quality monitoring data in the study area were used to calibrate and verify the parameters of the constructed SWMM model,and the parameters of the LID measures in the SWMM model were determined based on the previous results of this study.Then the SWMM model was used to explore the effects of LID combined measures on the control of rainfall runoff under different construction ratios and connection schemes.The simulation results showed that the R_Vs and R_Ls of various LID measures increased with the increase of the construction ratios.The R_Vs,R_Ls,and volume capture ratios of annual rainfall of the study area and the two subareas under series schemes 1 and 2 were always higher than those of not series schemes.Besides,the volume capture ratio of annual rainfall in series scheme 1 was higher than that in series scheme 2.Finally,the construction ratios of LID combined measures were optimized based on the response surface methodology.The optimization analysis results showed that the permeable pavement needed the maximal construction ratios(92.2%)when the volume capture ratio of annual rainfall of the first subarea reached the goal of 70%,followed by bioretention facility(88.9%),while the sunken lawn required the minimum construction ratios(50%).For the second subarea to achieve the goal,its bioretention facility needed the maximal construction ratio(82.0%).But if the study area reached the goal,the optimal construction ratio of LID combined measures would be between the optimal results of the two subareas. |
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