The Flow Near the Seabed: The Boundary Layer at the Bottom of Surface Waves

The wave-bottom boundary layer is a thin region near the seabed where vorticity generated by the adhesion of the fluid to the bottom is significant, while the flow outside this region is essentially irrotational in comparison. The importance of the boundary layer is due to several reasons: it is the place where most of the wave energy dissipation occurs outside the surf zone; the bottom friction is strongly dependent on the flow in the boundary layer; the sediment transport, both as bed load and suspended load, is most dependent on the flow in the boundary layer. This review presents the basic mathematical modelling of the boundary layer and describes the most relevant results available in the literature, obtained by experimental and numerical approaches. The mechanism leading to the generation of steady streaming is also illustrated, and the solution for the steady velocity component is worked out in analytical form for the case of linear waves propagating on a horizontal bottom and a laminar boundary layer.