A fundamental character of central bars hasn't been fully understood because there is a large difference of its existence form between natural river and laboratory experiment. For example, "mode degradation of central bars". This study indicates central bars don't degrade mode and keep its form in channel periodically repeats expansion and contraction. We found out conservation condition of central bars is closely related to channel plane form. This means existence form of central bars is never comprehended without combination of idea of area separation of sandbars and effect of channel plane form.
