Migrating Bedforms Generated by Solitary Waves

We present experimental results on the formation of streamwise asymmetric, migrating bedforms resulting from the transition of successive surface solitary waves (SSW) interacting with an initially flat sandy bottom. We analyze seven cases, with differing ratios between SSW height and water depth. For each experiment, we generated 400 SSWs having the same features, investigating their effects on the bed, in terms of near-bed velocity and erosional patterns. Our work proves that SSWs can generate asymmetric bedforms, similar in shape to dunes. The triggering process occurs in the region where the reverse flow induced by bottom boundary layer separation produces local erosion. The action of successive SSWs over the newly formed discontinuities gives rise to bedforms. Differently from steady flows, dune load decreases for larger wave-induced bottom shear stress.