RIPPLE FORMATION UNDER ASYMMETRICAL WAVES

In coastal environments, water wave propagation over non-cohesive sandy bottoms often causes the appearance of sedimentary structures called vortex ripples. Such bedforms induce a considerable modification of the bed roughness and, in turn, they affect the hydrodynamics inside the boundary layer at a large extent. At intermediate and shallow waters the near-bed flow may become asymmetrical and, in turn, ripples can show some degree of asymmetry due to nonlinearities of surface waves. The asymmetry of both flow and ripples has repercussions on the direction and the net rate of sediment transport (van der A et al., 2011). In order to quantify these phenomena the flow field and the geometry of sand ripples, i.e. ripple height η, length λ, steepness θ (η/λ) along with migration velocity of ripples (v) in asymmetrical flow conditions, such as those generated by waves propagating on a sloping beach, are here investigated.