Coupled modeling of bank retreat processes in the Upper Jingjiang Reach, China

Bank retreat processes in the Upper Jingjiang Reach (UJR) have attracted much attention in recent years due to a high occurrence frequency, and these processes can be influenced significantly by the near-bank fluvial erosion and variations in river stage and groundwater level. A coupled model was thus proposed in this study, integrating the module of bank-toe deformation with the modules of groundwater level change and bank stability analysis. The proposed model was validated through comparisons between the calculated and measured bank erosion volumes and bank profiles at four typical sections in the UJR, with relatively close agreement being obtained. Multiple tests were conducted to investigate the model performance. These results show that: (i) a more rapid drawdown of river stage resulted in a more significantly delayed response of groundwater level to river stage, indicating that the bank may suffer a higher pore water pressure at the same river stage during the rapid drawdown period; (ii) a larger bank erosion volume was predicted, with the delayed response of groundwater level being considered. In addition, initial groundwater level may take a great impact on bank erosion simulations, especially for the banks with relatively lower soil permeability and shear strength); (iii) based on the adopted method of bank stability analysis, the occurrence of the first failure may greatly influence the sequential failures, and thus the total number and volume of bank failure; (iv) the calculated bank erosion volume was most sensitive to a change in the critical shear stress, especially to its decrease, when the erodibility coefficient was determined by an empirical function of the critical shear stress. (c) 2018 John Wiley & Sons, Ltd.