| In recent years,with the changes in global climatic conditions,natural disasters have occurred more frequently than ever before,and secondary disasters caused by natural disasters have seriously restricted the development of the global economy.China is a country that is seriously threatened by natural disasters.Earthquakes,blizzards,floods,etc.have brought huge losses to our people and property.Because China has a low east and a high terrain in the west,the ground is washed away by rain all the year round,so many rivers with different shapes are formed.The effects of earthquakes and mudslides often block the river and form a natural dam..The dam body is a natural dam formed in the river channel due to the instability of the bank slope due to earthquake or super-strong rainfall in the upper reaches,and will bring catastrophic threat to the downstream residents.Due to the sudden formation of the dammed body,Therefore,it brings huge challenges to the forecast.Based on the previous studies,this paper proposes a set of evaluation methods for quickly calculating and predicting flooding of downstream urban floods in comb,ination with the hyperbolic fracture expansion method proposed by the academician Chen Zuyu and the basic ideas of downstream flood evolution.Taking the actual collapse of the Tangjiashan truss as an example,the DB-IWHR of the Tangkoushan is used to simulate the Tangjiashan truss collapse,and the fracture time-flow process line is obtained.The curve is used as the upstream boundary condition of the downstream flood evolution.Based on the flood evolution calculation,the hydrological factors and flood risk maps of the downstream river sections are obtained,which provides a basis for downstream personnel and property transfer decisions.The main research contents and results are as follows:(1)The water level of the sluice body—the storage capacity curve is an important basic data for calculating the expansion of the crater.Due to the suddenness of the damming body and the lack of measured data,it is very important to quickly obtain the storage capacity curve of the dammed body.In this paper,the GIS hydrological analysis method and superposition principle are used to calculate that the Tangjiashan stagnation reservoir has a storage capacity of 238 million m3 at an elevation of 750 m,which is 20.52%compared with the actual sluice water storage capacity.The calculated value is biased from the actual value.Small,the error range is about 20%-25%.Therefore,when the GIS hydrological analysis method and superposition principle are used to calculate the reservoir water volume storage capacity curve,30%is added as the esoteric feature storage capacity data based on the calculation results.(2)Time-flow curve at the break is the upstream boundary condition for downstream flood evolution.In this paper,the DB-IWHR outburst model and the HEC-RAS outburst model were used to simulate the Tangjiashan stagnation process.The DB-IWHR model calculates the peak flow of the fracture to be 7610 m3/s,while the measured value is 6500 m3/s,and the calculated value is about 17%larger than the measured value.The HEC-RAS collapse model calculates the peak flow of the fracture to be 17424m3/s,which is 2.6 times of the measured value.The time of the flood peak is 2.017h after the initial collapse,and the flow curve drops sharply after the peak flow.Therefore,using the DB-IWHR breakout model to calculate the peak flow of the plug body is better than the HEC-RAS model,and it can reduce the input error of the upstream boundary for downstream flood evolution.(3)Through the sensitivity analysis of the two model parameters of the DB-IWHR outburst model and the HEC-RAS outburst model,it is concluded that the dam break duration and the final crater bottom elevation are the main factors affecting the flood peak flow at the breach,and these two factors are determined.It is the material composition of the dam.Therefore,for the overall structure is relatively stable,the dam body is composed of a larger block rock mass,and the peak flow at the breach is generally small.(4)Calculate the results calculated by DB-IWHR as the upstream boundary conditions for the HEC-RAS flood evolution unsteady flow calculation,and calculate the calculated peak value of the flood peak flow of Beichuan Hydrological Station,Tonghekou Hydrological Station and Peijiang Bridge Hydrological Station.The measured value varies by about 2%,and the flood evolution calculation results are more reliable.By comparing the measured data and calculation results of the flood process lines of the three hydrological stations,it is concluded that the numerical simulation results of the process line and the measured results fit well before the flood peak flow of the three hydrological stations arrives.After the flow rate,the HEC-RAS flood evolution calculation flood process line is larger than the measured value.Compared with the measured data values,the calculated values of the maximum water depth of the three hydrological stations are too large,and the variation range is within 20%.According to the accuracy range of the Hydrological Information Forecasting Specification(SL250-2000),this error is within the acceptable range.(5)Combining the results of the flood evolution calculation with the geographical location information between Tangjiashan and Mianyang City,it is assumed that the area exceeding the maximum submerged water level elevation of the section is in the submerged area,and interpolation is considered when considering the flooding between the two sections in the river channel.The method gradually finds the submerged extent of the entire river channel,and finally obtains the maximum possible flooding range of the entire study area,and draws a flood risk map. |
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