| Due to the special geographical location,temperature and runoff and other hydrometeorological conditions,the ice flood disasters occur frequently and the disaster losses are very serious in the Neimeng section of the Yellow River.To explore the changing characteristics of ice situation and the influencing factors of ice flood in Neimeng section of the Yellow River,and to carry out the study of ice flood numerical simulation and ice flood risk zoning are of great significance for strengthening the construction of non-engineering measures for ice prevention and disaster reduction and ensuring the safety of residents’ lives and properties.The research results can provide support for the situation analysis and evaluation of ice prevention and disaster reduction and the formulation of risk prevention and control plans.In this paper,aiming at the practical problems of winter ice flood disaster in the Yellow River basin,such as strong sudden occurrence,great destructive power and difficulty in prevention and control,the Neimeng section of the Yellow River is selected as the typical ice flood analysis section,and the characteristics of ice flood change over the years and the influencing factors of ice flood disaster are analyzed.the coupling simulation technology of one and twodimensional ice flood backwater break and ice flood evolution and ice flood risk zoning are studied.The main research contents and results include:(1)The variation characteristics of air temperature,runoff,ice thickness and water storage increment in the Neimeng section of the Yellow River are analyzed by using MK method,linear analysis method and moving average method.The results show that the annual variation process of air temperature and trough water storage increment shows an overall upward trend,while the ice flood discharge and ice thickness show a downward trend as a whole,and the runoff sudden change points of Sanhuhekou station are 1966 and 1969.The abrupt change points of ice thickness in Bayangaole and Sanhuhekou stations are both in 1989,and the abrupt change points of trough water storage increment from Shizuishan to Bayangaole station are 1968.The abrupt changes of the above ice conditions are mainly distributed around 1968 and 1986,mainly due to the joint operation of Liujiaxia and Longyangxia reservoirs and the change of upstream water conditions.A comprehensive analysis of the variation characteristics of water storage increment,ice thickness and runoff in the trough shows that the change trend of air temperature is consistent with that of each ice condition,and the temporal and spatial distribution of each ice condition is the result of the comprehensive action of human activities and climate change.(2)The river bed-ice dam comprehensive roughness and ice-surface stratified roughness optimization method are used to construct the river-flood ice flood backwater burst submergence coupling simulation model.On the basis of calibrating and verifying the model,the inundation process under the condition of ice flood in different recurrence periods in Sanhuhekou,Sanchakou,Xinhekou and Shisifenzi on the north bank of the Neimeng section of the Yellow River is simulated respectively,and the temporal and spatial distribution characteristics of ice flood evolution in the study area of the Neimeng section are analyzed.The results show that the verification results of the model rate determination in Kuisu area are basically consistent with the actual inundation,and the model can meet the needs of ice flood numerical simulation and ice flood risk zoning.In the calculation results of the ice-flood coupling model of Sanhuhekou,Sanchakou,Xinhekou and Shisifenzi,the ice-flood velocity is basically less than 0.5m/s,and the inundation duration is more than 7 days.This shows that with the continuous evolution of ice flood,the evolution rate of ice flood is gradually slow,which is also consistent with the actual situation.The areas with large submerged water depth are mainly distributed in low-lying areas such as Xianfeng Township,Heiliuzi Township,Haizi Township and Sandaohe Township,which should also be used as key protection areas for ice prevention and disaster reduction.(3)Based on the calculation results of one-dimensional and two-dimensional coupling model of ice flood,the comprehensive risk degree method and single index analysis method are used to study the risk zoning of ice flood in the Neimeng section of the Yellow River,and the risk zoning of ice flood disaster is studied based on random forest(RF)algorithm and K nearest neighbor algorithm(KNN),and the spatial distribution characteristics of ice flood disaster risk are analyzed.The analysis of the results of ice flood risk zoning shows that the ice flood velocity index and inundation duration index are affected by the regional topography and the comprehensive roughness of the ice surface,and the ice flood velocity is smaller as a whole,and the corresponding inundation duration is longer.Therefore,in the calculation process of comprehensive risk degree zoning,the effect of ice flood velocity and submergence duration index is relatively weak,and the result of comprehensive risk zoning is similar to that of once-in-a-century submergence depth distribution.The areas with high risk are mainly distributed in Xianfeng Township,Gongzimiao Township,Heiliuzi Township,Haizi Township,Sandaohe Township and so on.According to the analysis of the results of the ice disaster risk zoning model,the high-risk areas of random forest algorithm and K-nearest neighbor algorithm are mainly distributed in Xianfeng Township,Gongzimiao Township,Heiliuzi Township,Qingdi Township and Sandaohe Township,which is consistent with the actual occurrence of ice disasters.And for the whole study area,the accuracy of random forest model and K-nearest neighbor algorithm are more than 80%.This shows that random forest algorithm and K-nearest neighbor algorithm have significant advantages in solving the classification and processing of multi-dimensional ice flood disaster data,which can not only ensure the accuracy of the algorithm,but also capture the relationship between multi-dimensional characteristic indicators and risk categories.Both the random forest algorithm and the K-nearest neighbor algorithm are suitable for the ice disaster risk zoning in the Neimeng section of the Yellow River. |
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