The Variations and Influences of the Channel Centerline of the Zhenjiang-Yangzhou Reach of the Yangtze River Based on Archival and Contemporary Data Sets

The Zhenjiang-Yangzhou reach of the Yangtze River is located at the top of the Yangtze River Delta, which is one of the most dramatic changes in the lower reaches of the Yangtze River. The study on the migration characteristics of the channel centerline is crucial for a comprehensive understanding of the river channel changes in the Zhenjiang-Yangzhou reach. In this study, a detailed calculation method is proposed to extract the channel centerline of the Zhenjiang-Yangzhou reach by using old maps and remote sensing satellite map and decompose it into seven parts. The spatial and temporal changes of Net Shift Distance (NSD), Cumulative Moving Distance (CMD), Migration Rate of Channel Centerline (MRCC) and Linear Regression Change Rate of channel centerline (LRCR) from 1865 to 2019 on the cross-section scale are studied. The results show that: (1) from 1868 to 2019, the channel centerline of the Zhenjiang-Yangzhou reach kept shifting. The average net displacement distance of the section is 1103.47 m on the right bank, and the average cumulative displacement distance of the section is 2790.51 m. (2) According to the NSD and CMD data of each part, the long-term movement direction of the channel centerline is basically the same, and a small part of the channel centerline has periodic reverse swing. The probability of channel centerline moving right is about twice that of moving left. At the same time, some rivers have high erosion risk. (3) Through MRCC and LRCR data, the total number of channel centerline moving left and right is 156 and 329, respectively, and the erosion risk level of the near half of the shoreline is high. (4) The change of river boundary conditions and hydrodynamic force will affect the migration rate and direction of channel centerline. (5) This study proposes a method to extract channel centerline from a braided reach and study its changes, which can be applied to other similar reaches with a long history of human activities and high density. The results enrich people's understanding of the long-term changes of a braided reach in the lower reaches of the Yangtze River and have certain guiding significance for river regulation, navigation safety, and revetment construction.