Monami as an oscillatory hydrodynamic instability in a submerged sea grass bed

Amala Mahadevan Woods Hole Oceanographic Institution, Woods Hole MA 02543 USA Abstract The onset of monami – the synchronous waving of sea grass beds driven by a steady flow – is modeled as a linear instability of the flow. Our model treats the drag exerted by the grass in establishing the steady flow profile, and in damping out perturbations to it. This damping leads to a finite threshold flow for the instability, which agrees with experimental observations. This role of vegetation drag differentiates our mechanism from the previous hypothesis that the Kelvin-Helmholtz instability underlies monami.