Evaluating the contribution of geotechnical and vegetation processes to lateral erosion in a meandering river reach using a holistic morphodynamic model

English Abstract:

Numerical models are increasingly being employed to examine the morphodynamics of meandering river channels. Although sinuous channels are typically associated with cohesive soils and vegetated floodplains, few models formally include these two elements. Furthermore, certain models reproduce the meandering planform and migration patterns observed in nature, but they require relaxed physics and rely on simplified floodplain morphology and process representation to study morphological changes at large spatiotemporal scales. As a result, they have a limited ability to quantify the relationships between key variables. The objective of this research is to evaluate the feasibility, relevance, and usefulness of including geotechnical and plant processes in a physics-based morphodynamic model. Two new modules were developed and coupled to the computational fluid dynamics model TELEMAC-2D for that purpose. A geotechnical module relies on a fully configurable universal genetic algorithm to detect unstable slopes in a fluvial valley represented by an unstructured mesh including a single- or multi-threaded channel, and to update terrain topography following planar and rotational slope failures. A vegetation module is coupled to the former to account for the mechanical effects of plant roots on slope stability. Topographic measurements from the semi-alluvial Medway Creek, London (Canada), are used to calibrate and validate the model. The model is then applied to fictive river channels to quantify the contribution of various biophysical conditions and hydrological regimes to river bank retreat rate.