This paper present an experimental approach on segregation phenomena of gravel mixed in water using an open straight channel and a large ball mill channel. Firstly, experiments in a large ball mill channel was carried out under various condition, i.g. two kinds of gravel mixed in water, bed velocity, with or without bed roughness. Occurrence conditions of segregation phenomena are categorized using mixture of water and gravel, and those results are compared each other with or without bed roughness. And movements of mixing water and gravel in ball mill are observed to find segregation mechanism.
