Spatial-Temporal Evolution Characteristics And Cause Analysis Of Different River Types In The Inner Mongolia Section Of The Yellow River

River course evolution is an important research direction of river dynamics,which is of great significance in river regulation,water conservancy engineering,ecological protection and so on.Under the dual effects of natural factors and human factors,the inflow and sediment conditions of the Inner Mongolia section of the Yellow River have changed significantly,and the river course evolution has intensified and the river course has been continuously silted.Therefore,the characteristics of the river course evolution of the Inner Mongolia section of the Yellow River also urgently need to be identified and studied from multiple perspectives,analyze the main factors affecting the river course evolution,and predict the river course evolution trend.The thesis takes the riverbed evolution of different river types in the Inner Mongolia section of the main stream of the Yellow River as the object,and analyzes the Inner Mongolia section of the Yellow River by using remote sensing technology and various statistical analysis methods based on the long-sequence hydrological and sediment,riverbed evolution measured data and continuous bend measurement data.The evolution law of plane morphology of different river channels and the law of horizontal and vertical changes of river channels have been studied.The velocity distribution and sand content distribution of continuous bends under different time scales and spatial scales have been studied,and the climate,water conservancy engineering.The influence of natural and man-made factors such as climate,water conservancy project,water and sediment conditions on river bed evolution is discussed.The results of the thesis have certain theoretical significance and practical value for revealing the evolution laws of different river beds in the mainstream of the Yellow River and enriching the water and sediment characteristics of continuous bends in natural river channels.Using remote sensing technology to extract river water body information,and analyze the plane morphology changes of different river types in the Inner Mongolia section of the Yellow River,the results show that the plane morphology of the upper section of the straight channel from Shizuishan to Bayangol has little change,and the lower section from Mengxi town to Balagong town has the characteristics of eight shape evolution.The wandering river section from Bayangol to Sanhuhekou has a large swing from left to right in each period,with scattered water flow and many sandbars.The beginning and end of the Sanhuhekou to Zhaojunfen reach little change in river pattern,and the river course changes in other regions are rather scattered.The plane change of the curved section from Zhaojunfen to Toudaoguai has little change,and the bend is relatively stable.Based on long series of hydrological and sediment data,statistical analysis methods are used to analyze the longitudinal evolution characteristics of different river types in the Inner Mongolia section of the Yellow River.The annual runoff and annual sedimentation volume of the Shizuishan station section of the inflow section and the outflow section of the Toudaoguai section have been significantly reduced.The sediment balance method is used to calculate the river erosion and siltation.The Inner Mongolia section of the Yellow River is in a silting state as a whole,with the median particle size The phenomenon of enlargement is obvious.Based on long series of hydrological and sediment data,statistical analysis and regression models are used to analyze the lateral evolution characteristics of different river types in the Inner Mongolia section of the Yellow River.Mapping the measured topographic data of large cross-sections,the large cross-sections of each station alternately scour and silt,the general siltation in the early flood period and the erosion in the late flood period,and the large flow in alluvial rivers is the main reason for the change in the location of the main channel.The relationship between the flow of each station and the hydraulic elements can be fitted with a power function model,and the fitting effect is good.The river facies coefficient decreases with the increase of flow and sediment transport.When the flow is greater than 1000 m3/s or the sediment transport is greater than 5 kg/m3,the river facies coefficient does not change with the increase of the flow and sediment transport,and the channel tends to be stable.The second-order polynomial regression model is the best fit for the relationship between the flow of the river section and the change of water level.As the flow increases,the sediment transport rate of the river channel increases.Due to the regulation and storage operation of the reservoir,the incoming flow continues to decrease and the river sediment transport capacity decreases.Based on the measured flow velocity,sediment content,particle size gradation and topography of the river section,the hydrodynamic characteristics and sediment transport characteristics of the bend are analyzed.The existence of ice cover changes the distribution of water flow velocity.During the ice-covered period,the vertical velocity distribution is parabolic or "3";the position of the maximum measuring point of the vertical during the free flow period is close to the water surface.The position of the maximum vertical velocity of the curve section is close to the concave bank,and the vertical position of the maximum sand content is close to the convex bank.During the freezing period,the median particle size of the crest section is the largest.The Mann-Kendall non-parametric test method was used to test the water and sediment abrupt changes.The mutation points of the annual runoff at Shizuishan Station and Toudaoguai Station were both in 1990.After 1998,the annual runoff at Shizuishan Station and Toudaoguai Station had a significant downward trend.There is no sudden change point in the annual sediment discharge at Shizuishan Station.After 1972,the annual sediment discharge at Shizuishan Station has a significant downward trend.The annual sediment volume of Toudaoguai Station began to change suddenly in 1985,and the annual sediment volume of Toudaoguai Station decreased significantly after 1987.The change of runoff is mainly affected by the combined operation of Longyangxia and Liujiaxia reservoirs,and there is a delayed response.The change in sediment discharge at Shizuishan Station is affected by the operation of Liujiaxia Reservoir,and there is also a lagging response.The change in sediment discharge at Toudaoguai is affected by the combined operation of Longyangxia and Liujiaxia Reservoir,which has already begun to appear during the construction period of Liujiaxia Reservoir..The evolution of the Inner Mongolia section of the Yellow River is jointly affected by natural and man-made factors.The main factor analysis results show that the erosion and deposition of the Inner Mongolia section of the Yellow River before 1986 was mainly affected by runoff.After 1986,the erosion and deposition of the Inner Mongolia section of the Yellow River was mainly related to sediment transport.The amount is significantly correlated.The construction and operation of water conservancy projects changed the original water and sand conditions,and it was also the main reason for the river course evolution after 1986.