| Global climate change leads to frequent extreme precipitation events.With the dramatic changes and expansion of urban underlying surface caused by rapid urbanization,the phenomenon of "looking at sea in city" in China has become increasingly worse.At present,in the content of the vigorous construction of sponge cities in China,it is of great significance to explore the role of the LID in mitigating urban waterlogging and implement the risk management for urban waterlogging,which is meaningful for leveling up urban rain-flood resources management and enhancing the waterlogging prevention and reduction capacity.In this research,the Sponge Campus of Tianjin University is taken as the study area.Based on physical experiments as well as numerical simulation,the urban hydrological effect and waterlogging risk under low-impact development are studied.The main research contents and achievements are as follows:(1)On the basis of the self-developed artificial rainfall simulation experiment system,the prototype of LID measures in the study area was scaled to the indoor experimental scale for rainfall runoff and infiltration experiments.The results show that the runoff coefficient of experimental permeable concrete and grass-planting brick is much lower than that of the conventional development,but grass-planting brick is better in reducing the total and peak runoff and delaying the runoff peak.The infiltration process of two kinds of permeable pavements can be described by the Horton infiltration model.The initial infiltration rate of permeable concrete is large,but it decays quickly.The infiltration process of grass-planting brick decays slowly,meanwhile,the stable infiltration rate and overall infiltration capacity are higher than that of permeable concrete.(2)Based on the results of LID experiment and the basic data of the study area,a coupling model of SWMM and MIKE 21 in the study area was constructed,and the influence of single LID measure removal and density reduction of LID measures on the surface hydrological process was studied through scenario setting.The results show that in frequent light rain,the biological retention cell exerts the optimal effect on runoff control,and with the increase of rainfall,permeable pavement performs better.Permeable pavement is quite effective in inundation area and water depth control with stable performance,followed by the biological retention cell.The sunken greenbelt has relatively limited effect in controlling runoff and inundation characteristics.The frequent light rain is sensitive to the density of LID measures,and even a small proportion of LID measures is able to control runoff effectively.When the density reduction ratio of LID measures is small,it has little influence on runoff,while it has great influence on inundation area.After the rainfall reaches a certain level,reducing the LID measure density by a small percentage has little effect on the increase of inundation depth.(3)Through scenario setting and urban waterlogging risk assessment,the flooding alleviation effect and waterlogging risk under low-impact development within the study area were analyzed.The results show that under low-impact development,the reduction effect of runoff,inundation area and risk area is obvious,while the mean inundation depth,mean velocity and mean ponding duration are insensitive to LID measures.The waterlogging risk in the study area is mainly caused by the long-term ponding due to insufficient drainage capacity of the drainage network.The waterlogging risk is insensitive to flow velocity,and the possibility of danger brought about by water flow instability in the study area is quite small.The inundation duration is a vital factor influencing waterlogging risk in the study area.After considering the inundation duration,the waterlogging risk in the study area is generally increased by one level,and the HR threshold method is inapplicable in plain cities,thus there is a situation that the waterlogging risk is overestimated. |
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