Modelling River Flow Through In-Stream Natural Vegetation for a Gravel-Bed River Reach

Abstract

Macrophytes (aquatic vegetation) are known to modify river flow by reducing local velocities, increasing turbulence generation, and reducing channel conveyance capacity resulting in increased flow depth. Understanding flow response to vegetation change is imperative to inform flood mitigation strategies, however the field is nascent with much uncertainty surrounding the estimation of flow conveyance in vegetated channels and, subsequently, the best vegetation management practices and possible flood risk. Therefore, in order to develop an understanding of how macrophytes modify flow conveyance modelling techniques must be developed which can effectively represent the three-dimensional effect of natural vegetation within an open channel flow environment. This study simulated vegetation-flow interaction using a 3D finite-element modelling method to investigate the feasibility to which a vegetated natural gravel-bed river can be represented using the drag-force approach. Two methods of parameterising vegetation-induced drag were explored to investigate the effect of flow behaviour within a vegetated gravel-bed river reach.