The method of low dams series is a mean that control debris flow and flooding. One unit of the low dams series consists of three or more dams, having a height of 1-2m, and the distance between dams is about 50m. Vertical drops of water flow at dams, varying between 0 and 1.3m. In a unit of low dams series, vertical drop of the dam locating downstream varies much more than those of upper dams do. The drops sometimes exceed the ability of upward passage for fish. However, low height of dams gives much advantage to fish passage.