| In history,the ice disaster of the Yellow River has become a very prominent natural disaster in rivers in winter and spring in China due to complicated pregnant environment,strong unexpectedness and difficulty in prevention and control.The Inner Mongolia reach has frequent disasters in the ice flood season due to its unique geographical position,river direction and climatic conditions.In this thesis,the problem of ice prevention and disaster reduction in Inner Mongolia river section under changing environment is systematically studied.Linear trend method,Mann-Kendall test method and water body index method are used to extract the sustainability and catastrophic regularity of Ice flood disaster causing factors;The law of erosion and deposition evolution of the river channel under the dam of Haibowan hydroproject is clarified qualitatively and quantitatively by using the transverse and longitudinal shape analysis and section topographic method;Based on HEC-RAS software,a one-dimensional hydrodynamic model of the river channel under the dam is established to simulate and analyze the temporal and spatial distribution characteristics of the river hydrodynamic force in the free flow period and the ice flood season and its driving mechanism to the ice regime;On this basis,the operation mode of ice prevention dispatching of Haibowan hub is discussed.The main research results are as follows:(1)During the ice flood season in Inner Mongolia from 1961 to 2015,the temperature change experienced three stages:cold winter period(before 1987),warm winter period(1988～2004)and relatively warm period(after 2005).There was a sudden change in the 1980s,and the temperature increase was the most obvious in the 1990s;The discharge in the periods of ice-run and thaw is significantly affected by the operation of Haibowan junction;From 2000 to2020,the main channel of the river swings obviously and develops towards bending,and the change rate of channel width in ice flood prone areas is more than 30%.(2)Affected by the construction and operation of Haibowan hydroproject,the section adjustment of different forms of river channel under the dam can be divided into three types:main channel scouring,beach channel uniform scouring and silted beach channel.The longitudinal thalweg has experienced the change process of lifting first and then cutting down;The evolution process of channel erosion and deposition has experienced three stages:deposition(2004～2012),erosion and deposition transition(2012～2014)and erosion(2014～2020);After 2014,the average annual scouring volume of the river channel under the dam is 9.159 million m~3,and the scouring intensity is171.26m~3/(m·a).In terms of spatial distribution,DM20～DM12 reach is most significantly affected by the hub operation,accounting for 52%of the total scouring volume.(3)HEC-RAS software is used to simulate one-dimensional unsteady flow of river under dam.The maximum relative error of water level and flow rate is 13.29%and 14.55%respectively.Analysis of the simulation results shows that:The water level of the river gradually rises during the free flow period,fluctuates during the ice flood season and reaches the highest level during the stable seal period.The smooth flow period of the river flow is of single peak type,with peak and minimum values in the flood season and dry season respectively.The spatial distribution of the ice flood season presents three types:stepped type,exponential type and peak type.The cross-section flow rate has a sudden change during the transition period of ice flood.The section DM12～DM11,with sharp change of flow rate and distribution of bends and dangerous workers,should be taken as the key section for ice protection of the river under the dam.The comprehensive water level-flow-flow rate relationship indicates that the stable sealing period for flood risk of rivers under dam is embankment,while the flowing period and opening period are rivers.(4)The flow control schemes for five ice flood seasons of Haibowan junction are proposed,and the one-dimensional constant flow simulation is carried out by HEC-RAS software.Through the analysis of the changes of water level and velocity,it is concluded that:During the ice flood season,the discharge control of Haibowan hydroproject is implemented according to800m~3/s in the flood period,750m~3/s in the stable sealing period and 550m~3/s in the river opening period,which is the most favorable for the ice control situation of the river channel under the dam. |
