Quantifying the Spatial and Temporal Variability of Drag within an Aquatic Vegetation Canopy

Abstract:

Vegetative drag acts as a control upon flow structure and sediment dynamics within vegetated river channels. Drag removes energy from the flow, leading to lower mean velocities and increased turbulent kinetic energy which can both selectively increase and decrease local sediment transport. Therefore understanding the magnitude and distribution of vegetative drag is key to understanding flow-vegetation-sediment interaction.

Here, we present results from combined hydraulic-biomechanical modelling of flow through an aquatic vegetation canopy using a dynamic vegetation model coupled with a Large Eddy Simulation of the flow. This allows for dynamic reconfiguration of the stems in response to the flow which acts to decrease the magnitude of drag.

The results illustrate the variability in drag due to the stem reconfiguration as well as other factors such as wake sheltering further into the canopy. The results show that the stem-averaged drag coefficient differs significantly from the value for a rigid cylinder and that vegetative drag within a canopy exhibits variability in both space and time.