High resolution modelling of flexible submerged vegetation in rivers

Abstract

Vegetation is a common feature within natural river channels and exerts a profound influence on the functioning of the fluvial system. In particular, the interaction between vegetation and flow causes a reduction in conveyance, an alteration to the velocity profile and the generation of coherent turbulent structures which differ to those found in un-vegetated channels. Recognition of the influence of vegetation on open channel flow has led to an increased awareness of the importance of accurately representing the effects of vegetation within numerical models, across a range of spatial scales.

This thesis introduces two novel biomechanical models, capable of simulating the complex interaction between flow and vegetation at high spatial and temporal resolution. The development and validation of these models permits investigation of flow-vegetation interactions across a range of plant types and flow conditions. These models are applied to a range of scenarios providing new insight into the interaction mechanisms between the vegetation and the flow. In particular, this thesis focuses on the role of turbulent structures in driving flow-vegetation interaction.

The results presented in this thesis support existing theories for simple canopy flows, whilst also proposing additional interactions in the case of more complex canopies. In addition, key findings relating to the role of drag in controlling flow-vegetation interactions are explored.

Finally, through the development of a third, lower resolution, vegetation model, this thesis begins to explore how the process understanding gained from application of the high resolution models may be upscaled to the reach scale models which are central to river management.