Instability-driven material exchange in flow through deformable, buoyant seagrass bed

The monami phenomenon results from the interaction of fluid flow and deformable, submerged seagrass beds. This interaction results in a shear instability that drives a collective waving amongst the grass blades, vortex generation in the free streaming fluid above the bed, and potentially material exchange between the bed and the fluid. Using a two-phase, coupled numerical model, we investigate how the instability and vortex strength are functions of the fluid Reynolds number and the grass buoyancy, which dictates grass deformability in the model. Then, using both a scalar field and Lagrangian particles, we evaluate the flux dependence on the instability strength and grass waving. As the vortices become sufficiently large, there is the potential that neighboring vortices will interact as they propagate down the channel. The conditions for vortex interactions and their impact on material transport out of the bed will also be presented. Finally, as the vortices travel down the channel, they entrain material from the bed. To better quantify the downstream transport, a coherent structure analysis is performed to evaluate the bounds of the materially coherent vortices.