Vertical Sorting and Armoring of Bed Mixtures during River Bed Degradation

Grain size variations of bed materials with time and space during river bed degradation are measured in an experimental flume. It is observed that the bed surface sand becomes much coarser than the original sand mixture during the bed degradation. This coarsening of the bed surface sand is analyzed with a vertical sorting model of sand mixture in the moving layer on the bed surface, while the final armor coat formation during the parallel bed degradation is analyzed by the longitudinal sorting model.