Multi-scale modelling of river morphodynamics

We developed a morphodynamic model for generation and migration of dunes under shallow flow approximation. The flow was calculated by two-dimensional depth-averaged equations and the bed shear stress was found by fitting a log-low function at each grid cell. The shear stress then was adjusted by adding slope effect. As the bed features have smaller spatial scales than the flow, a two-grid approach is adopted. The flow is solved on a coarse grid and then the flow field is interpolated on a finer grid, on which the bed morphology is calculated. This technique enabled us to solve the morphological process for large scale applications. A parameterized relation is applied for bedload sediment transport and the bed evolution is updated using Exner equation. Two cases with different flow conditions are simulated and compared with experimental results and field measurements. The computed results show good agreement with experiments and field measurements.