Modelling morphodynamic development in the presence of immobile sediment

Predicting the formation and break-up of immobile layers is of crucial importance for river management, as these processes greatly affect the morphodynamic evolution of the river bed. Two models are currently available for studying these processes: Struiksma's and Hirano's model. In this paper, we show that both models present limitations. This is done by numerical modelling of a laboratory experiment and two thought experiments. Struiksma's model does not predict break-up and Hirano's model yields unrealistic results when part of the sediment is immobile. We propose two alternatives that overcome these limitations: the ILSE and HANNEKE models. They differ in the interpretation of the top part of the bed interacting with the flow. Moreover, only the HANNEKE model explicitly predicts the formation of coarse layers, at the expenses of a more limited application range.

Automated summary

Predicting the formation and break-up of immobile layers is crucial for river management, but the existing models have limitations. Through numerical modeling experiments, this paper finds that Struiksma's model cannot predict break-up and Hirano's model produces unrealistic results when sediment is immobile. To overcome these issues, two alternative models, ILSE and HANNEKE, are proposed. The HANNEKE model explicitly predicts the formation of coarse layers, but it has a more limited application range.