Boundary Shear Distribution in Open Channel Flow

Boundary shear distribution in both rough and smooth open channels of rectangular and trapezoidal sections is obtained by direct measurement of shear drag on an isolated length of the test channel utilizing the technique of three point suspension system suggested by Bagnold. Existing shear measurement techniques have been reviewed critically. Comparison of the measured distribution has been made with other indirect estimates, from isovels, and Preston tube measurements, based on Keulegan's resistance laws. The discrepancies between the direct and indirect estimates are explained. Of the two indirect estimates the surface pitot tube technique is found to be more reliable. The influence of secondary flow on the boundary shear distribution could not be accurately defined in the absence of a dependable theory on secondary flow.