  The transport of sediments by a fluid flow is commonly found in nature and in
industry. In nature, it is found in rivers, oceans, deserts, and other
environments. In industry, it is found in petroleum pipelines conveying grains,
in sewer systems, and in dredging lines, for example. This study investigates
experimentally the transport of the grains of a granular bed sheared by a
turbulent liquid flow. In our experiments, fully developed turbulent water
flows were imposed over a flat granular bed of known granulometry. Under the
tested conditions, the grains were transported as bed load, i.e., they became
entrained by rolling and sliding over each other, forming a moving granular
layer. The present experiments were performed close to incipient bed load, a
case for which experimental data on grains velocities are scarce. Distinct from
previous experiments, an entrance length assured that the water stream over the
loose bed was fully developed. At different water flow rates, the moving layer
was filmed using a high-speed camera, and the grains' displacements and
velocities were determined by post-processing the images with a numerical code
developed in the course of this study. The bed-load transport rate was
estimated and correlated to the water flow conditions.
