COMPUTATION OF BED SHEAR STRESS FROM VELOCITY MEASUREMENTS IN A GRADUALLY VARYING ROUGHNESS BED

Abstract

An experimental study was conducted in a gradually varied roughness bed by using a Particle Image Velocimetry (PIV) system. The local bed shear stress was evaluated from four distinct methods: the log-law, the Reynolds shear stress (RSS), the vertical turbulence intensity and the turbulent kinetic energy (TKE) methods. These methods provided significantly different results owing to discrepancies in the boundary conditions and change in local flow structures resulting from the bed roughness.