Abstract
It is generally considered that, differing from the pipe flow, the flow in open channels has a free surface and waves appearing on water surface relate to some extent with the laws of resistance to turbulent flow in open channels. According to this idea, the instability of flow is connected with the mixing length of turbulence, and then computing the velocity distribution by Prandtl's equation, Froude Number is added to Reynolds Number in the laws of resistance ot turbulent flow in open channels. Applying this theory, experimental results by the author, Dr. Matsuo and R. W. Powell with smooth open channels can be explained all over the regions of subcritical and supercritical flows, and therefore, the difference between the laws of resistance to turbulent flow in pipe and that in open channel can be made clear.
