Hydrodynamics of Gravel Bed Flows: Implications for Sediment Transport

Bottom of the mountainous rivers is generally composed of natural gravels. Flow depth in such rivers is generally shallow, with the ratio of water depth to size of bed materials (known as relative submergence) rarely higher than 20. In this type of flow, gravels intrusion induces significant spatial varation of the flow characteristics at the near bed region, which is known as roughness layer. The simultaneous effects of natural gravels and water surface cause formation of complicated flow structure which is to some extent different from the flow with high relative submergence (flow with relative submergence higher than 40). Despite abundance of studies in shallow flows, there are only a limited number of studies concerning spatial organization of near bed flow field for such type of flow, with also contradictory results. In present study, Stereoscopic Particle Image Velocimetry (SPIV) at near bed horizontal layer and Digital Particle Image Velocimetry (PIV) in vertical planes are employed together with laser scanning of bed elevations to study flow field and turbulence structure over a coarse immobile gravel bed in submergence conditions ranges from 5 to 10. Spatial organization