Experimentae Study on Flow Resistance over Gravel Surface

Resistance law of the open channel flow with a small relative water depth is remarkably different from that with a sufficiently large relative water depth. Investigations about the resistance law have not been confirmed. There are many phenomena not to be revealed. In relation to the resistance law, wall shear stress has been obtained inferably in consideration of the mean velocity distribution or the resistance formula deduced from the logarithmic velocity-distribution law. For flows of thin shear layer with roughness, strong turbulent field attributed to the roughness plays an imporant role to the resistance law, there are some questions about the deduction of the wall shear stress with preceding considerations, According to the above point of view, the wall shear stree is measured directly with a servo typed shear stress meter. Using the measured wall shear stress, the vertual wall height, the friction factor of Darcy-Weisbach, Manning's roughness coefficient and Chezy constant are obtained. Using these factors it is shown that the resistance law depends primarily on the roughness Reynolds number for the flow in the completely rough region, although the resistance law depends on the relative water depth under the logarthimic velocity-distribution law.