Relation Between Riparian Vegetation And Meander Migration For Typical Meandering Rivers In The Yellow River Source Region

Meandering rivers are generally developed in the Yellow River source region,where its formation and evolution can affect the distribution of the riparian vegetation.In turn,the riparian vegetation also inhibits the erosion of the concave bank and promotes the sediment deposition of the convex bank,which forms a key scientific issue of meandering river evolution.In this study,the in-situ investigation of the Lanmucuo River in the Huangnan steppe and the White River in the Zoige basin of the Yellow River source region were carried out during the summer of 2016-2017 to obtain the hydrodynamics,geometry,bank material and other data.The relation between riparian vegetation and the evolution of meandering rivers was studied.The migration rates are indirectly measured by slump blocks and tree rings of riverbank,which put forwards a new way for obtaining evolution data of meandering rivers.The main influcing factors of migration rate and the process of vegetation succession were analyzed and the main research results are as follows:According to the analysis of the slump blocks in Lanmucuo River,a method for estimating the migration rate of the river bend was proposed,and the results were 0.02-0.2 m/a.Five different vegetation communities are formed in the convex bank,which correspond to different period of vegetation succession.The time required for the primary succession to each vegetation community was calculated.It takes more than a hundred years for a river bend evolution from start to finish.A multiple linear regression model was established based on the regression analysis of the migration rate with potential influcing factors.The results showed that the vegetation biomass and the elevation difference between floodplain and main channel are the functions of the migration rate in Lanmucuo River.That is,the vegetation biomass is inversely proportional to the migration rate,and the elevation difference between floodplain and main channel is proportional to the migration rate.The vegetation along the convex bank of the White River is zonal distribution.The size gradient of the trees and the convex bank profile changes along the axis of the convex bank.The tree cores and disks were collected and processed,and the distribution and tree rings data were obtained.A method for calculateing the migration rate by tree rings and their distance was put forward,and the migration rate of the White River was 0.28-6.1 m/a by drawing the tree-age distribution map,which is basically consistent with the migration rate estimated by remote-sensing image.A multiple linear regression model was established based on the regression analysis of migration rate with its potential influencing factors,showed that the flow velocity and river slope are the main influencing factors for the migration rate.The rate is proportional to flow velocity and river slope,and the effect of flow velocity is greater.Based on the statistical analysis of slump blocks along the river bend,it is found that the cutoff has a significant impact on the upper and lower reaches within 3 km,resulting in a large number of bank collapse.And the riverbed will be continuously adjusted after the cutoff.near the cutoff,the slump blocks are the most dense and the erosion amount is the largest.The erosion amount decreases along the distance in both directions.According to the different erosion rates on the left and right sides of the river,the direction of future river meandering is inferred.