APPARENT SHEAR STRESS IN A COMPOUND CHANNEL

ABSTRACT

During the flow of in a compound channel section, there is always transfer of momentum between the deep main section and the adjoining shallow floodplains. This interaction mechanism has the effect of increasing floodplain shear and decreasing main channel shear. Experiments are carried out to measure the boundary shear around the wetted perimeter of a two-stage compound channel that helps to quantify the momentum transfer in terms of apparent shear stress along the assumed interfaces originating from the junction between main channel and flood plain. Analysis of the apparent shear is useful in deciding the choice of appropriate interface plains for developing stage-discharge relationship of a compound channel. In the present work, a modified expression to predict the boundary shear distribution in compound channels that is good for all width ratios is derived and is found to provide significant improved results, when validated using the well published data.

KEY WORDS:

• Apparent shear
• Boundary shear
• Interface plane
• Compound channel
• Floodplain
• Main channel
• Overbank flow
• Momentum transfer