Comparative Analysis Of Channel Morphology Characteristics And Analysis Of Causes In The Upper Reaches Of The Yellow River And The Yangtze River

As the most sensitive geomorphic unit in the process of geomorphic evolution,rivers play a key role in the process of surface erosion,material transport and deposition,and record rich information of geomorphic evolution,tectonic activity and climate change.With the development of river dynamics erosion models and the improvement of the accuracy of topographic data sets,the correlation analysis of non-equilibrium patterns of rivers can obtain rich information on tectonic deformation,erosion deposition and climate change.Both the Yellow River and the Yangtze River originate from the eastern margin of the Tibetan Plateau and flow out from the northeast and southeast directions respectively.Based on the 30-m resolution ALOS DEM,this paper firstly extracts the basic topographic factors of the Yellow River and the upper Yangtze River basins,including slope,aspect,topographic relief,surface roughness,surface incision depth,and hypsometric integral,so as to quantitatively obtain the macroscopic geomorphic features of the two basins and analyze the spatial distribution pattern of the basic topographic factors of the basins;secondly,it extracts the channel networks of the Yellow River and the Yangtze River basins.After determining the channel concavity index,we used the integral method to calculate the accurate channel steepness index,based on which we identified the location of the two types of knickpoints and realized the quantitative characterization of the knickpoints;finally,we explore the causes of channel morphology in the upper Yellow River and the upper Yangtze River basins by combining the effects of tectonic faults,geological lithology,climatic rainfall,geological disasters,glacial action and other factors.The results of the study show that(1)The distributions of topographic factors such as slope,relief,surface incision depth and the direction of the knickzones in the study area are obviously correlated.The distribution of each value in the Yangtze River basin is wider,and the extreme values are larger.The topographic features are more influenced by rivers,and the high values are mostly distributed on both sides of rivers,while the consistency between the distribution of topography and the direction of rivers in the Yellow River basin is not obvious;the HI value of 0.59 and the area elevation integral with obvious convexity in the Yangtze River basin indicate that The topography of the Yangtze River basin is in the critical state between young and old stage,and the interaction between rivers and topography is strong;while the HI value of 0.44 in the Yellow River basin indicates that it has experienced long-term weathering and denudation,and is in the late stage of old age,and the topography is more stable.(2)The quantitative analysis of the channel morphology of the upper Yellow River and the upper Yangtze River basin shows that the overall channel morphology of the Yellow River basin is bounded by the Ruoergai basin,and the longitudinal profile of the upper river is up-concave,with few knickpoints and the overall topography is more stable;the longitudinal profile of the lower river is up-convex,and the channel is generally in an uneven state,with variable steepness indices and widely developed knickpoints,which indicates the variability of the uplift rate of this river section and the upward convexity of the longitudinal profile of the Yangtze River basin is more obvious,and the steepness index changes drastically,and the number of knickpoints is larger and more densely distributed,indicating that the river dynamics in the Yangtze River basin is more intense than that in the Yellow River basin,and the interaction with the surface is more obvious,and also in a stronger state of transient adjustment,while the slopebreak knickpoints are distributed in a laminar pattern,which also proves that the laminar distribution of slope-break points also proves the multiple changes of uplift rate in the Yangtze River basin.(3)The causes of rifting in the upper reaches of the Yellow and Yangtze rivers are complex,responding to tectonic,faulting,climate,geological hazards and glacial factors,and the causes of rifting can be effectively determined through comprehensive analysis of the nature,size and geological factors of rifting.The slope-break knickpoints are usually caused by tectonic activities,climate change and glaciation,and will keep moving upstream;while the verticalstep knickpoints are usually caused by faulting,lithological differences and geological disasters,and are distributed on fault or stratigraphic lines,and are usually constant in spatial location.