Low Reynolds number erosion in vegetated arrays

Semi-aquatic and aquatic vegetation plays a vital role in geological processes such as erosion. Understanding how the flow properties, nature of the sediment bed and vegetation affect soil erosion is key to developing nature-based strategies to promote soil retention. Field studies have shown that, in natural systems, vegetation can limit erosion. At low Reynolds numbers, flow through finite porous media such as vegetation exhibits three distinct flow regimes: rake, where the flow is diverted around the hair array; sieve, where the flow passes through the array; and deflection, a transitional regime in which the flow partially penetrates the array and is redirected laterally. In this work, we investigate the impact of vegetation on the erosion of a granular bed. We develop a lab-scale model, which consists of a square array of cylinders attached to a rotating arm in a tank of fluid at rest. We characterize the flow with PIV and recover the three flow regimes. We then add a granular material at the base of the model vegetation. We compare the erosion patterns under different flow regimes for model vegetated and non-vegetated sediment beds. These results should further the understanding of natural erosion processes and advance the development and efficiency of nature-based strategies to reduce erosion.