Bank erosion under the impacts of hydraulic erosion, river stage change and revetment protection in the Middle Yangtze River

Bank failures in alluvial rivers are a typical soil-water interaction problem, which is related to many factors including the direct action of flow, river stage change, and human actions (such as bank revetment). To investigate the failure mechanism of protected riverbanks and possible factors affecting their stability, we analyzed data measured from a typical reach of the Middle Yangtze River. Furthermore, we performed numerical simulations of seepage and stress variation inside the riverbank. The field observation and simulated results indicated that: (1) Hydraulic erosion by near-bank flow remains the primary factor influencing the erosion of the protected riverbank. However, the bank protection works effectively limit the lateral bank retreat but increase the incision of the nearby riverbed, with the largest erosion depth of 10.6 m during August to November in 2020. (2) The initial damage in protected banks may be triggered by local tensile stress concentration during the water-rising period, under the combined actions of hydrostatic confining force, pore water pressure and gravity. This initial damage will progress into more severe bank failure events, particularly during the flood period. (3) After the regulation of the Three Gorges Project, the increased changing rate of river stage (~1.6–2.5 fold) could potentially increase the risk of damage to protected riverbanks in the Middle Yangtze River.