Research On Countermeasures And Implementation Paths Of Pluvial Flooding In The Perspective Of Spongy City

Global climate change has lead to a rise of atmospheric water vapor in the eastern monsoon region of Asia.Thus,the frequency of extreme precipitation events have a rising trend.Urbanization has increased the hardened surface and enhanced the urban heat island effect.The combined effect of climate change and urbanization has made urban hydrological characteristics changed a lot,mainly manifested by the increase of surface runoff.Once the pluvial flooding occurs in urban areas,it often leads to serious social and economic effects,especially in large cities like Shanghai.In recent years,how to effectively cope with pluvial flooding has become an urgent problem that scholars and governments pay close attention to.In China,a new method for pluvial flooding mitigation that called “spongy city” has been put forward,and it has gradually been applied to the practice of water regulation.In this study,Shanghai is selected as a research area for its high frequency of pluvial flooding.And this study mainly focuses on three aspects: the exploration of the pluvial flooding mitigation theory and realization ideas from the perspective of sponge city;development and optimization of an pluvial flooding simulation tool;design of the spongy city construction path in the study area to mitigate the pluvial flooding based on the scenario analysis method.The main achievements and conclusions of this study are summarized as follows:(1)Based on the problems in current urban pluvial flooding research,the main concerns of the study of sponge city include: the scale effect and the measure connection of the sponge city system;the design of pluvial flooding treatment scenarios;quantitative evaluation of mitigation degree.After determining the focus of the study,we take Shanghai as example to design the implementation of the scale division and connection of sponge city measures.And it is recommended to make scenario plans combined with simulation to evaluate the effect of the sponge city system quantitatively and optimize the original plans.(2)For the needs of quantitative evaluation the mitigation effect of sponge city,a simulation tool for urban pluvial flooding simulation is developed.To improves the simulation precision,the the CN value of runoff generation module and the Manning coefficient of confluence module are optimized.It shows that the simulated water depth is more consistent with the total rainfall after optimizing the CN values.And the effect of terrain and the material of land surface on the hydrodynamic process is more obvious after optimizing the Manning coefficient.(3)To test the sensitivity of drainage and impervious surface in pluvial flooding process,the sensitivity verification scheme are designed.The result of drainage sensitivity test shows that when the discharge period of drainage is raised to 3 and 5 years,the water reduction rate is about 30%~60%.The result of impervious surface sensitivity test shows that when the impervious surface ratio returns to 66% and 61%,the water reduction rate is about 10%~65%.To select the most suitable and feasible combination of drainage capacity and impermeable surface rate,60 sets of drainage infiltration scenarios are rearranged and simulated.The simulated result shows that when the return period of drainage reaches 5 years and the water surface rate is reduced by 10%~15%,the amount of water under the return period of 100 years can be reduced around 40%~50%.And the detailed methods to improve the drainage and infiltration capacity are stated.(4)In order to connect the small scale with the mesoscale,4 regions in the downtown area of Shanghai are selected to conduct a case study.By analyzing the characteristics and water control objectives of study areas and the effects,applicability and cost of the source rainwater control measures,we select the most applicable ones and make the detailed layout plans.Calculation results indicate that all the case study areas have the potential to keep the water depth below 150 mm when facing a rainstorm in 100 years.For the 4 study areas have their representative land use structure,and the measures applied in each area are various,the results have promotional value and the measures can form a source rainwater control measures system in the downtown area of Shanghai.