Migration characteristics of a meandering river: The Madhumati river, Bangladesh

Linearized 1-D models are widely used to simulate morphodynamic behavior of natural meandering rivers. Ikeda et al. (1981) developed a linear solution to predict near-bank excess velocity based on shallow water flow model. In their approach, bank erosion rate is linearly related to the near-bank excess velocity through an empirical erosion coefficient. Hasegawa (1989) proposed a bank migration model, which is based on the same linear relation as Ikeda et al.'s, but includes the erosion rate formula that is derived from integration of sediment continuity equation. This study aims to investigate whether these meander migration models are able to reproduce the observed behavior of a meander bend of the Madhumati River (Bangladesh). Simulation results show that near-bank excess velocities are small in the upstream of bend apex, reach to the maximum value at bend apex and then decrease in the downstream. Correspondingly, the bank migration follows the same trend. The agreement between predicted and observed migration is good in the upstream of bend apex, but the migration is underestimated in the downstream of bend apex. On the contrary, when an influence of the near-bank excess flow depth on the bank migration is added to Hasegawa's model, it is able to simulate the downstream migration well. Although the near-bank excess velocities and observed near-bank excess flow depths were out of phase, they together amplified the bank migration rate, which resulted in shifting the migration towards the downstream direction. However, this method necessitates careful estimation of flow width from asymmetrical cross-sections at bend.