Numerical simulation of bank erosion and accretion in a braided reach of the Lower Yellow river

Abstract

The braided reach of the Lower Yellow River (LYR) often experienced dramatic channel evolution during flood seasons, with both bed and bank deformations occurring simultaneously, which led to several negative effects such as land loss, channel migration and overbank flooding. A coupled one-dimensional model was proposed to simulate both bed evolution and bank deformation, including three modules of flow-sediment transport, bed deformation, and bank erosion and accretion. The proposed model was applied respectively to simulate the longitudinal and lateral channel deformations in the braided reach in the years of 2018 and 2006, in order to conduct detailed processes of model calibration and verification. The results indicate that: the proposed model can accurately simulate the flow and sediment transport processes, and the majority of the Nash-Sutcliffe efficiency coefficients (NSEs) were larger than 0.60 between the calculated and measured hydrographs of water discharge, water level and sediment concentration at different sections, with the maximum value up to 0.96; the calculated erosion and accretion widths of the riverbanks closely agreed with the measured data, and the absolute errors between the calculated and measured post-flood reach-scale bankfull widths were 18 m in 2018 and 14 m in 2006, with the relative errors of 1.7% and 1.3%; the effects of riverbank deformation on sediment discharge, flow velocity and channel deformation were also analyzed, which indicate that the module of riverbank erosion and accretion can play a significant role in predicting hydrodynamic and morphodynamic processes in the braided reach of the LYR.