Experimental works in a sinuous open channel were performed to identify the vortical structures. Although the nature of such vortices are 3D and they mainly associated with low-speed and low-pressure zones in channel, the hypotheses of 2D models for the prediction of phase lag and bed topography seems to be satisfactory. In the theoretical part of the present paper by the use of the dynamic equation in the lateral direction for a curved open channel an equation for the velocity distribution in the lateral direction is extracted. Then, assuming a sine-generated channel whose curvature is a function of its longitudinal position, the phase lag between the secondary flow and the main flow is obtained. Next, by the use of different assumptions for the flow characteristics, different phase-lag formulas are extracted. Finally using the concept of incipient motion, variation of bed topography in a complete wavelength of a sine-generated open channel is presented.
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