Determination of Apparent Shear Stress and its Application in Compound Channels

The momentum exchange in the mixing zone of compound channel is a common phenomenon and has an important effect on discharge estimation. It can be quantified with apparent shear stress (ASS) at the interface of floodplain and main channel. The mechanisms of apparent shear stress are investigated. A strong relationship between apparent shear stress and difference of squared velocity at each compartment has been found. The variations of geometrical shape ratio and roughness ratio have been introduced. Improved formulas of calculation of apparent shear stress (ASS) have been proposed for symmetrical compound channels with regression analysis on the basis of a large amount of experimental data and the formulas have been validated with other data. The importance of roughness ratio in roughened compound channels is noted. Discharge estimation with ASS method gives a good agreement with experimental results. Compared with other methods the improved formulas present a high degree of accuracy. It is applicable to small scale and large scale compound channels.