Response Relationship between Channel Morphological Adjustment and Bank Collapse in Typical Reaches of the Middle Yangtze River

Abstract

Based on daily discharge and water level data from Shashi and Luoshan stations, Landsat remote sensing images, fixed cross-section topography, and bank collapse records in typical reach of the middle Yangtze River, this study integrates Mann–Kendall trend analysis, water body index extraction, cross-sectional analysis, and other methods to investigate the evolution characteristics and driving relationships of discharge–water level variation, shoal-bar erosion and deposition, cross-sectional adjustment, and bank collapse. The results indicate that: (1) Runoff exhibits a pattern of “increased low-flow period, and stable flood-season flow,” while water levels show a significant annual decline, reflecting the dominant control of channel incision on water level changes. (2) Between 1987 and 2017, pre- and post- Three Gorge reservoir operation, the shoals shifted from substantial rightward migration to localized erosion, with dramatic cross-sectional adjustments (e.g., the thalweg of cross-section Jing-178 dropped by 10.9 m, and the right bank of Jing-182 retreated by 1200 m). (3) From 2003 to 2024,the cross-sectional areas of the low-water channel and bankfull channel increased by 2,600 m² and 4,050 m², respectively, indicating pronounced erosion expansion. (4) Bank collapses were concentrated at the right bank of Jing181 (16 events) and the left bank of Li8 (10 events), displaying stage-specific activity. (5) Bank collapse length is highly positively correlated with cumulative erosion and deposition volume of the low-water channel (R² = 0.84), indicating that lateral erosion of the low-flow channel is a key factor in bank slope instability. These findings provide a scientific basis for channel evolution understanding and bank collapse prevention.