Numerical And Physical Simulation Of Ice Flood Evolution Process In The Upper Reaches Of The Main Stream Of Heilongjiang River

Ice flood is a complex hydrological process under the combined action of various factors such as river boundary conditions,thermal conditions,and hydraulic conditions.The upper reaches of the main stream of Heilongjiang River have special geographical location and special climatic conditions.Flowing through the middle and high latitudes,there is a latitude difference between the upstream and downstream rivers.Often,the temperature difference caused by the latitude difference causes the upstream break-up before the downstream,forming an ice flood.Once ice flood occurs,it will cause serious damage to hydraulic structures,river navigation,ecological environment and the safety of life and property of people on both sides of the river.Therefore,in this paper,aiming at the evolution process of flooding in the upper reaches of the main stream of Heilongjiang River,through the combination of numerical simulation and physical model test,this paper simulates the evolution of the typical river section in the upper reaches of the main stream of Heilongjiang River,and explores the influence mechanism of the hydrodynamic change process of the flooding.Therefore,this paper combines the hydrodynamic model with the physical model test to simulate the evolution of the flood in the upper reaches of the main stream of Heilongjiang River,and explore the influence mechanism of the hydrodynamic change process of ice flood.The detailed research contents are as follows:(1)Based on the measured data of natural rivers,a hydrodynamic model of the Beihong section and Sidaoka section of the upper reaches of the Heilongjiang River is established.By changing the settings of flow and ice thickness conditions in the model,the water surface elevation and flow velocity verity were observed when the flow is 50m~3/s,100 m~3/s,200 m~3/s,500 m~3/s,1000 m~3/s,and the ice thickness is 1.0m,1.2m,and 1.4m.The influence mechanism of flow rate and ice thickness on the hydrodynamic change of flood was explored,and the evolution law of river flood under different flow conditions and ice thickness was obtained.By comparing the hydrodynamic change process of different river sections under the same hydraulic conditions,it is verified that the river terrain conditions play an important role in the formation of ice floods.The research results show that the flow and channel topography have a great influence on the hydrodynamic changes of the flood evolution,and the backwater height in the upper reaches of the river increases with the flow.Under the same working conditions,the high water level in the upper reaches of the Beihong section of the Mohe is much larger than the hydrodynamic model of the Sidaoka section of Huma,and the topographic conditions of the river have a greater impact on the hydrodynamic process of the ice flood evolution.Under different ice thickness conditions,with the increase of ice thickness,the increase of the water level in the upper reaches of the river channel is small,and the ice thickness is not the dominant factor in the hydrodynamic change during the break-up period,and has little effect on the water level of the river channel during the break-up period.(2)Simulate an example of the evolution process of the flood in the upper reaches of the Heilongjiang River during the break-up period,according to the measured data of natural rivers,a hydrodynamic model of the Luogu River section where flood disasters are frequent is established.The measured hydrological data were used to calibrate the channel roughness under different working conditions to ensure the calculation accuracy of the hydrodynamic model.The hydrodynamic process of the river during the break-up period of the Luogu River section in 1991,1994,1995,1996 and 1999 was simulated.Due to the lack of measured ice thickness data in the Luogu River section,based on the meteorological data in the Mohe area where the Luogu River section is located,established the daily ice thickness model of the Luogu River section under different working conditions,and the hydrodynamic change process over the years was obtained.Comparing the hydrodynamic calculation results with the high water head in the upper reaches and the start and end dates of the ice dam with the actual ice dam data to verify the rationality of the model calculation results.The results show that compared with the measured data,the hydrodynamic model of Luogu River section established in this paper has better simulation effect,and the model calculation error is small.Verify the feasibility and accuracy of the hydrodynamic model in the hydrodynamic simulation of the ice flood.According to the hydrodynamic simulation results of the Luogu River section during the,it is concluded that the water level elevation and flow velocity along the Luogu River section change with the evolution of the ice flood during the break-up period:during the flood evolution process,the water level in the upper reaches of the Luogu River reaches the peak first,and then dropped suddenly,and finally tended to a stable trend.However,with the increase of the upstream overflow section,the flow velocity gradually decreases;after the ice dam collapses,the flow velocity distribution gradually tends to be stable.(3)Simulate the mechanical ice-cover break-up hydrological phenomenon that often occurs in the upper reaches of Heilongjiang River through physical model tests.An indoor water tank was used to simulate the boundary conditions of the river channel,the paraffin wax property with similar physical properties to natural ice was used to make model ice,and the composite wood board nearly as wide as the river channel was used as the simulated ice layer.By controlling the upstream inflow conditions,observing the flow law and accumulation state of the flow under different hydraulic conditions,monitoring the force of the flow on the unthawed ice layer downstream,and combining mechanics to explore the formation mechanism of the ice dam flood,the evolution law of the flow under different hydraulic conditions is obtained,and the resulting drift ice loads.The results show that under different hydraulic conditions,the accumulation forms of the drifting flow are different.When the"inverted open river"occurs,when the Froude number of the front edge of the unopened ice sheet is less than the critical ice Froude number,the drifting flow occurs in a juxtaposed type of accumulation;When the ice Froude number is greater than the critical ice plug,the flow will mostly form a hydraulic thickening ice plug;the ice Froude number continues to increase,and the flow will transition from the hydraulic thickening ice plug to the hydraulic thickening ice plug.By analyzing the force of the simulated ice sheet,the force characteristics of different types of ice plugs on the unthawed ice sheet are obtained.