Research On Flood Evolution And Damage Assessment Of Floods In Floodplains、stagnant And Overflow Areas Of Xian County

At present,flood hazards remain one of the most destabilizing factors threatening human development.In recent years,with the frequent occurrence of extreme rainstorm events,domestic and foreign water management ideas have increasingly focused on the use of engineering measures such as dams and embankments in combination with non-engineering measures such as flood management.Therefore,flood storage area construction,management and enabling studies play an increasingly important role in the flood control system.In this paper,flood evolution simulation and flood damage evaluation and application studies are carried out for the flood storage and stagnation area in Xian County under high flow rate and super standard flood conditions.The mathematical model of flood evolution simulation mainly includes the one-dimensional river model,the two-dimensional floodplain evolution model and the interface of the one-and two-dimensional models.Flood damage evaluation mainly assesses the losses of enterprise,agricultural and household properties,and the applications include risk zone classification and disaster level evaluation.In this paper,firstly,to address the problems of lagging flood propagation,unstable flow and higher water level in the downstream than in the upstream due to general grid ordering,the proposed sequential arrangement method of finite volume grid is adopted to make the calculation results conform to the actual situation of river flood evolution.The floodplain evolution model takes into account the topographic conditions and buildings such as railroad and highway in the lagging area,and establishes a two-dimensional unstructured grid model for complex terrain.The oneand two-dimensional models are coupled and connected using the weir flow formula,and their information interactions can be divided into two types: free weir flow and inundated weir flow.The model is basically reliable as verified by the information of the current overflow capacity of the river.The flood evolution mathematical model is used to simulate the evolution of floods with different recurrence periods.The 1-in-10-year flood is only used to flood in the river;the 1-in-20-year and 1-in-50-year floods are activated to store water in the Xian County flood storage area;and the overflow area is activated to flood in the1-in-100-year overtopping flood.In the categorical loss assessment model,the flood loss rate is obtained based on historical flood surveys and reference to similar areas,reflecting the functional relationship between flood characteristics information and flood losses.By spatially distributing the information of various types of properties and flood inundation characteristics,the direct losses of floods in the 20-year and 50-year flood storage areas in Xian County were assessed to be 1.17 billion yuan and 1.555 billion yuan,respectively,and for the 100-year case,the preliminary estimation of losses in the overflow area was made,and its direct losses were about 92 million yuan.According to the Flood Disaster Assessment Criteria,the disaster levels caused by the 1-in-20-year and 1-in-50-year floods to the flood storage area were assessed,and the flood storage area in Xian County was calculated to be a larger flood disaster.The risk classification of Xian County flood storage area was calculated by using the multi-factor risk degree index method to calculate the risk degree index of villages,and the flood risk maps for different reoccurrence periods were drawn based on the linear maps of inundation etc.to provide a basis for local safety construction.