Spatial And Temporal Variation Analysis Of Lower Yellow River Channel Based On Remote Sensing Image

As a typical wandering channel,the lower Yellow River is of great research value in the evolution law of wandering channel.In the lower Reaches of the Yellow River above Gaocun,the flow is wide and shallow,and the sandbar is developed,which is easy to silt and good at scouring and swinging frequently.In order to control the Yellow River,many scholars have made corresponding studies on the change of the lower reaches of the Yellow River.Most scholars take the measured data as the main research data to analyze the changes of the lower Yellow River channel,and remote sensing images have the advantage of fast data extraction.Therefore,this paper takes remote sensing images of the garden mouth of the lower Yellow River as the main data source,supplemented by measured data.By means of fractal theory and the calculation of river facies coefficient,the evolution law of this channel in time and space is analyzed.Through the hydrologic data of discharge,sediment concentration and sediment transport,the causes of the variation of the lower reaches of the Yellow River are analyzed.This paper selects the appropriate remote sensing image to extract and analyze the water body,and then vectorize the image.By using the average river width and channel area measured from the figure and combining with the measured flow data,the calculation of river phase coefficient and channel bending coefficient is completed.Box counting method is used to grid the picture and the fractal dimension value of corresponding channel is calculated by counting the number of grids.Through analysis and research,the following conclusions can be drawn:(1)From 1995 to 2016,the overall river facies coefficient of huayuankou channel in the lower Yellow River showed a regular trend of change,dropping by 31.24%,and the bed making capacity of the riverbed was gradually weakening.The average river width of the lower Yellow River is constantly narrowing.(2)Within the year,the fractal dimension value of the lower Yellow River reaches the maximum value in flood period,and the fractal dimension value after flood is smaller than that before.The value of wet season is above 1.55,and the data fluctuates greatly.However,the overall trend of the dry season is decreasing,by about 0.1.It shows that the wandering pattern of the lower Yellow River is weakening and gradually changes to the direction of the river type.(3)The bend coefficient of the river decreases from 1.28 to 1.22,which is consistent with the above trend.The bend coefficient of the river decreases year by year,and the trend of straightening increases continuously.Compared with river bends,river bends with smaller angles change more,so the trend of river course changes more slowly.(4)The correlation between fractal dimension value of river channel and measured data is greater.The leveling bank flow is in a relatively stable state,and the downstream water passage capacity is not affected.In this case,the above channel changes may continue to occur.Since the construction of various reservoirs,the flow,sediment transport and scouring and silting of the river channel have gradually developed to a regular direction,so human activities are the fundamental cause of the changes of the river channel.