Evaluation of the Various Methods of Shear Stress Determination in a Sharp Channel Bend with Developed Topography

Shear stress is one of the important parameters in river flow studies and has a key role on river patternand also estimating the amount of erosion and sedimentation of fluvial material within the river.Therefore, estimating this parameter in different positions of the field flow, especially next to the riverbed and banks, is vital. Despite doing intensive studies by many researchers on the amount of shearstress and its distribution in straight and curved channels, due to the complex flow regime within thebends, more studies have to be carried out. In this research, the results obtained from various methodsof shear stress estimation are compared with those obtained by using of mean velocities and theirfluctuations taken by an ADVP instrument. The compared methods include Reynolds shear stress,Turbulent Kinematic Energy, and Logarithmic Profile, have been previously used and compared instraight channels, but never have been used and compared in a sharp bend. The results obtained fromthe study on a 1930 bend with developed topography showed that unlike the straight channels, thestrong 3D flow changes the Reynolds stress patterns in sharp bend, so that there is no specific order toget a reliable estimation of bed shear stress in this type of channels. Moreover, because of the effectsof strong secondary current, the longitudinal velocity profiles in sharp bends are flatter than those instraight channels, and hence there are some uncertainty regarding using logarithmic profiledistribution. The results of this study showed that in general, the Logarithmic method to estimate thebed shear stress gives better results among the available mentioned methods.