A flow in a smooth open channel can he divided into several regions along the flow direction, i. e. the laminar boundary layer, transition region, turbulent boundary layer, fully developed turbulent boundary layer and a uniform open-channel turbulent flow. The temporal mean and turbulent characteristics will not vary again in the course of the uniform open-channel flow. There is obviously a structure of different regions in the vertical direction of a smooth open-channel turbulent flow. The limits of different regions, the velocity profiles and characteristics of fluctuating velocities in such regions are given. When the aspect ratio W/H is larger than 10, the flow in the open channel may be considered as a 2-dimensional flow. The formulas of sectional averaged velocity and frictional loss factor are also given.
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