| Xiangjiang River is the largest river in Hunan Province.It originates from Shiti,Baishi Township,Xing’an County,Guangxi Zhuang Autonomous Region.It originates from ocean and flows into Dongting Lake from south to north.The central cities in Hunan,such as Changsha,Zhuzhou,Xiangtan,Hengyang and Yongzhou,are all built along the Xiangjiang River.The central cities of Hunan Province are all under the subtropical monsoon climate.During the flood period,there is the risk of overflowing levees and rainstorm and waterlogging.There have been many large-scale floods in the history of Changsha City,such as the great flood in 1998.In recent years,with the rapid development of China’s economy,the pace of urbanization in Changsha City is gradually accelerating,and the area of urban area is increasing,which makes the flood disaster factors change compared with the previous years.For example,in July 2017,a large-scale flood disaster occurred in Hunan Province,Changsha hydrological station broke through the highest water level in history,and the flood overtopping brought serious impact to the urban area of Changsha City,and brought a huge threat to people’s life.However,there has never been such a large-scale flood overtopping phenomenon in Changsha City before.It can be predicted that with the continuous acceleration of urbanization,overtopping flood will become the main flood causing factor in Changsha City.Therefore,in order to reduce the property loss of citizens and make Changsha citizens fully and timely understand the flood risk information of Changsha City,and to make timely prevention work when the flood season comes,this paper will use the model to analyze the flood overtopping evolution process of Changsha City.In this paper,based on the field survey data of Xiangjiang River and one-dimensional Saint Venant equation,one-dimensional channel model of Xiangjiang River and Liuyang River is established.Based on the terrain data of 14m accuracy and two-dimensional shallow water equation of Changsha City,two-dimensional hydrodynamic model of Changsha City is established by unstructured grid.On this basis,one-dimensional and two-dimensional models are coupled by weir formula,and one-dimensional urban channel model is established A two-dimensional coupling model.Based on the theory of dry and wet water depth and roughness zoning,the two-dimensional model is optimized;based on the land use map of Changsha City,the two-dimensional terrain model of Changsha City is divided into roughness zoning to generalize the building land,green land,forest land and other surface water blocking structures;at the same time,the road,embankment,railway and other linear water blocking structures are generalized in the form of dense grid;in the real river On the basis of channel survey points,the inverse distance weight interpolation method is used to interpolate the channel,extract the channel section,and divide the roughness of different river sections.On the basis of a two-dimensional coupling model,this paper simulates and verifies the process of flood overtopping in July 2017 in Changsha City.On this basis,the historical maximum discharge flood in Hunan Province in 2019 and the flood process in 2017 are combined to calculate the historical maximum discharge flood process,and on this basis,the flood overtopping evolution process under the historical maximum discharge flood process is calculated and analyzed,and the flood overtopping area,submergence depth and flood front evolution distance under two conditions are compared and analyzed Based on these factors,this paper gives the location of Changsha vulnerable to inundation and the areas that need to be paid attention to,makes further detailed analysis of these areas,and obtains inundation points of flood,which provides support for flood control planning and decision-making in Changsha. |
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