The Analysis Of Urban Flood Trend In Nanjing Urban Area

Urban cover is not only the reflection of the natural changes, but also the result of human activities. The temporal spatial distributions of urban cover is one of the key influence factors of urban flood. The urbanization changes the overall of urban cover, as well as the spatial distribution pattern. This paper focuses on the trend of urban flood problems under the influence of vegetation. Taking Nanjing urban area as an example, the methodology combining of qualitative and quantitative analysis as well as the theory and numerical simulation are adopted, which aimed at exploring the urban flood on the influence of vegetation. The main contents and conclusions are as follows:1) Analyzing the time series and spatial distribution change of urban cover in the study area. The result shows that the vegetation cover ratio is about 30% of Nanjing urban area.The process of urban cover conversion makes the distribution structure of the building more concentrated, which aggravated the impact of urban flood disasters.2) Urban flood simulation model including the surface runoff and ground confluence based on the method of hydrology and hydrodynamics, established under the influence of the urban cover change to analyze the effect of vegetation cover on urban flood. Vegetation affects the runoff flux of catchments, and the vegetation spatial distribution among catchments causes different flux. Road crossing and low terrain become the inundation area due to vegetation cover and drainage pipeline nodes.3) The typical areas are chosen to explore the influence ofvegetation cover on urban flood. The existence of vegetation cover not only can decrease the submerged area, but also have a certain impact on submerge flux. There is a negative correlation between runoff coefficient and land cover area. When the vegetation cover area is above 40%, the runoff coefficient will reduce to 60%. The spatial distribution pattern of vegetation cover have an effect on urban flood. Vegetation cover can alleviate the urban flood flux when located on upstream and delay flood when located on middle position. The downstream position of vegetation cover could accommodate the inundation, which can not be ignored.Above all, the rational distribution of vegetation cover can reduce the damage of urban flood, which could supply the technical support for urban flood control. In order to reduce the loss of urban flood disaster, this paper may provide the scientific reference on the basis of urban flood numerical simulation.