Influence of lateral flow contraction on bed shear stress estimation by using measured turbulent kinetic energy

Abstract

Sedimentation, including erosion, transport, and deposition of river-bed material, is a complex process influ-enced by several parameters related to flow, materials, and geometries. Evaluation of the bed shear stress under a wide range of flow conditions is the primary step in understanding the sedimentation process. In this study, the bed shear stress is analyzed experimentally near an obstruction where maximum erosion occurs. The local flow conditions near the obstruction are varied by modeling several typical lateral flow contractions in the flume. Through analysis of the results, we discuss the effects of local turbulence on the bed shear stress in terms of Reynolds stress and turbulent kinetic energy that are measured for various ranges of water depth, velocity, and flow contractions. From the findings, we suggest an empirical correction factor that accounts for the local tur-bulence in calculation of bed shear stress using turbulent kinetic energy. It is concluded from experiments that the empirical correction factor is a function of the flow contraction ratio.