213 / 2024-02-28 07:42:39

Planform Evolution of a Channel Composed of Non-Cohesive Heterogeneous Sediment

bank erosion,sediment sorting,2D numerical modelling,bar formation

Abstract: Bar formation and bank erosion are two processes that interact with each other and significantly impact the river morphodynamics and channel pattern formation (meandering or braided channels), specially during the occurrence of disasters. Several factors affect the formation of bars, for instance, sediment heterogeneity and sediment supply coming from the banks. The sediment supply from the bank affects the bar formation and as reported by previous researchers it can increase the wavelength of the bar and the formation of bars can lead to local widening of the cross sections.

While bar formation processes cannot be fully captured by linear and non-linear stability theories, numerical models become an option to study these processes.

In this study, we perform numerical simulations to study the interaction between channel dynamics and bank erosion interaction by using a 2D-depth averaged numerical model. In the simulations, a variable size distribution and a bank erosion model that uses a stretchable grid to capture the bank evolution was employed. We tested the numerical model in an experimental flume from the literature that consisted of an initial straight channel that develops into a meandering channel. The bank erosion model was tested to reproduce the experimental conditions.

In the flume experimental channel, the bank height was ~4 times larger than the flow depth, therefore the supply of sediment from the banks is large, affecting the bed evolution by accumulating material in the downstream part of the channel. The simulation results reasonable agree with the initial formation of alternate migrating bars, and it was observed that the larger sediment deposited on the top of bars while finer sediments were found in the pools; however, the calculated bank erosion was underestimated compared to the experimental results.