Abstract: The evolution of alternate bars in straight channel under different discharge and sediment conditions was studied in this research via generalized flume model experiment. The conclusions are as follows: (1) The area and size of alternate bars in straight channel declined with the reduction of sediment load from the upstream, and simultaneously the spacing between bars became shorter. (2) The downward movement speed of alternate bars decreased as the sediment load from the upstream decreased. In the case of large sediment load supplied from the upstream, siltation at the end of bars compressed the mainstream nearby, thus causing the beachhead of the opposite bank to move downstream. Such phenomenon was weakened when the sediment supplied from the upstream reduced. (3) In the presence of large sediment load from the upstream, the alternate bars were scoured although the principal channel was in deposition. With the reduction of sediment load supplied from the upstream, the channel was scoured instead. The deep trough which was close to the river bank sometimes would not be filled when alternate bars moved downstream, leading to the formation of inverted watercourse.

Key words: straight channel, alternate bars, fluvial process, discharge and sediment conditions, flume experiment