When beds constituted of sediment particles are submitted to shearing flows, the particles at the surface of the stream-bed are able to move as soon as hydrodynamic forces acting on them exceed a fraction of their apparent weight. Bed-load refers to the transport of the sediment carried by intermittent contact with the stream-bed by rolling, sliding, and bouncing. This situation occurs in a wide variety of natural phenomena, such as sediment transport in rivers, and in industrial processes, such as problems due to hydrate formation in pipeline that are encountered in oil production and granular transport in food or pharmaceutical industries. This talk will discuss (i) critical condition for incipient motion of the grains, (ii) bed-load transport, and (iii) it will show that the evolution of the particle bed in a closed pipe exhibits different dune patterns as the flow is increased from laminar to turbulent regimes.