Analysis Of Beach And River Regime Evolution In Wandering Reach Based On Multi-source Image Information

At present,the wandering section of the lower reaches of the Yellow River is within the control of the rectification project,and the river course still maintains strong wander ability,which is prone to large banks and river potential changes.In view of this situation,image information,as a tool that can intuitively reflect the changes of river activities,is a favorable means to study the characteristics of bank beaches and river potential changes in the wandering section of the lower reaches of the Yellow River.This paper studies the characteristics of wandering rivers through image information technology,and analyzes the evolution characteristics of bank beaches and river potentials in the lower reaches of the Yellow River based on remote sensing images from a macro perspective,as well as the response relationship between water and sediment changes and bank beaches and river potential changes.From the local perspective,UAV+PIV technology was used to study the evolution characteristics of the wandering mainstream zone of the lower reaches of the Yellow River.From these two perspectives,the evolution characteristics of banks,beaches,and river potentials of the wandering section of the lower reaches of the Yellow River were comprehensively controlled.The main research contents and achievements are as follows:(1)The cluster unsupervised classification method was used to extract the river channel information of Zaoshugou～Caogang control and guidance project in the flood period and nonflood period in 2013～2022,and the indicators reflecting the changes of the bank beach(the length of the south shoreline,the length of the northern shoreline,the area of the south bank beach,the area of the north bank,the area of the heart beach)and the change of river potential(river activity area,average width of river channel,river channel overlap,mainstream line length,main line bending coefficient,and average swing of mainstream line were proposed).The evolution characteristics and trends of shore beach and river potential indicators in three types of time periods: "inter-annual flood period","interannual non-flood period" and "intrayear flood period compared with non-flood period" were elaborated in each study interval,and the evolution characteristics of bank beach and river potential in the study section were analyzed and summarized from two aspects: "stability of each study interval" and "change trend of bank beach and river potential indicators".(2)The period of peak fluctuation of water and sand conditions is the follow-up fluctuation period of the evolution of bank beach and river potential indicators,and in the case of different magnitude of water and sand,the corresponding bank beach and river potential indicators also have corresponding change laws,which are specifically manifested as: the length of the shoreline on the north and south sides,the area of the beach on the north and south banks,the length of the main line,the bending coefficient of the mainstream line and the average swing index of the main line are inversely proportional to the amount of sand coming from the water;The overall indicators of river activity area,heart beach area,river channel overlap and river channel average width showed a positive relationship with the amount of sand coming from the incoming water.(3)The proportional relationship between the flight altitude H of the UAV and its viewport length L and width B is: L=1.15 H,B=0.6469 H.According to the characteristics of stable flight attitude and accurate positioning of UAV,UAV is a good mobile river flow image acquisition device.UAV+PIV technology uses the ripple feature of the river surface as a particle tracer object to measure the flow velocity,and flight sampling should be avoided when the river surface is reflected.According to the measurement results of the flow meter and the surface flow field results analyzed by UAV+PIV technology,the relative error is only 1.2%～1.7%,and the direction of particle movement trajectory of the flow trace is consistent with the flow field,which determines the accuracy of the surface flow velocity and direction measured by UAV+PIV technology.According to the surface flow velocity and position distribution of the river channel cross-section measured by UAV+PIV technology,the rationality of the main line of the three studied river sections in Madu,Weitan and Heigangkou was verified.(4)The evolution characteristics of the mainstream zone between the flood season and the non-flood period in 2022 were as follows: the surface flow velocity of the mainstream zone was proportional to the flow size,so the average surface flow rate of the mainstream zone in the Madu,Weitan and Heigangkou sections was 2.4,2.6 and 1.81 times that of the non-flood period,respectively.The angle between the surface velocity of the main stream zone and the south bank and the distance between the main stream zone and the south bank of the main stream zone were obviously affected by the heart beach of the river channel,so under the influence of the heart beach during the non-flood period,the main stream belt of the Madu and Heigangkou river sections moved to the south bank,and the main belt of the Weitan section moved to the north bank.The largest variation of the angle between the surface flow velocity and the south bank of the mainstream zone of each studied river section was as follows: the downstream side flood period of the Madu River section was greater than the average of about 8° during the nonflood period.The section of Weitan River is at 1100～1400 m,and the non-flood period is about20° greater than the flood period;The section of Heigangkou River is-500～200 m,and the nonflood period is greater than the average of about 4° during the flood period.The main stream showed the greatest change in the distance from the south bank as follows: the non-flood period of the Madu River section moved about 155 m south at-200～1500 m compared with the flood period.Compared with the flood period,the non-flood period of the Weitan River gradually moved 420 m from 10 m to the north at-570～1000 m.The non-flood period of the Heigangkou section moved about 110 m south at-500～500 m compared with the flood period.