Sediment erosion in flexible canopies by vortex impact

A model experiment with a vortex impacting a flexible canopy filled with a thin homogeneous bed of particles is presented. Flexibility of the filaments increases the efficiency of resuspension by the amount it allows the effective canopy-height to reduce due to the reconfiguration of the flexible structures. Scaling of the results with the effective canopy height leads to a collapse of the observed resuspension in the history of several successive impacts. It is further shown that preferential pathways in the canopy play a large role in resuspension. When comparing a hexagonal arrangement to a random arrangement of the filaments at the same average porosity, one needs to double the amount of impacts to achieve the same average resuspension. Hence, it is concluded that the random path of the particles around the filaments is affected in a non-linear manner by the local resistance. Regions of locally sparse arrangements of the filaments cannot balance the trapping effect of particles within regions of dense arrangement in their travel history. Flexibility of the filaments again proves a better resuspension under such conditions. (c) 2020 Elsevier Ltd. All rights reserved.