Movable Bed Armoring and Sediment Transportation

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Armored bed surface, which is composed of particles coaser than those of the parent material, can be produced even if in the conditions that all the particles of bed material are transported. The material of subsurface is usually finer. This emphasizes that an another mechanism except selective entrainment exists in the armering process of bed sediment.A multi-layer model, in which both the selective entrainment on bed surface and the vertical exchange of grains between surface and subsurface layers are taken into account, is prenosed. The model enables the bed material of surface to be coaser and that of subsurface to be finer. Flume tests are performed in conditions with no sediment supply as well as with sediment feeding. Particle size distributions are measured during the runs for transported sediment and bed layers. The results predicted with the model are compared well with data from the flume tests for spatial and temporal changes of those particle size distributions.