ABSTRACT: Surface gravity waves generate oscillating currents whose magnitude drops exponentially with depth. In sufficiently shallow water (relative to the wavelength), the horizontal component predicted by the inviscid solution does not vanish at the bottom boundary, which gives rise to a boundary layer, turbulent under most geophysical conditions, extending a few centimeters from the boundary. This layer is usually embedded in the larger boundary layer generated by steady or pseudo- steady currents. The combined boundary layer controls the exchange of momentum and mass (sediments, contaminants, etc.) between the bottom of the ocean to the rest of the water column. In this talk we use Large Eddy Simulation as the primary tool to investigate several aspects of the physics of this type of boundary layer, with particular emphasis to sediment entrainment and suspension. Both layers over a hydrodynamically smooth boundary, as well as over ripples are considered. The latter form naturally under moderate waves and introduce several interesting new features to the problem. The work done so far show how modern computational tools developed in the last 20 years can be successfully applied to tackle geophysical problems, and highlights the need for a closer integration of geosciences with basic engineering.