Numerical Exploration of the Morphodynamic Regime Diagram for Straight Channel River Flows

Self-organising phenomena play a crucial role in river systems, from the catchment scale to the single morphological unit. Many studies on morphological patterns in straight channels have been conducted, but full regime diagrams in fundamental parameters (e.g. aspect ratio and mobility parameter) are not known yet.  However, determining such morphological regimes is crucial for prediction of river dynamics and consequently for a range of applications, from flood risk assessment to ecological management and restoration projects.

This study employs a 2D numerical model based on spectral methods to explore these morphodynamic regimes in a straight channel, a first approximation of most existing managed rivers. The model couples the depth-averaged shallow-water and continuity equations for the flow and the Exner mass-conservation equation for the sediment. The morphological patterns arising from the simulations are explored in a wide range of parameter space, beyond the critical values for bar formation used in perturbation methods. A thorough taxonomy of planforms and their complexity is generated, resulting in a morphodynamic regime diagram for straight channel flows. Moreover, both the spatial and temporal characterisation of the solutions is carried out, and the presence of quasi-periodic and chaotic behaviour is investigated.