Assessment of Turbulence Parameters in Natural River Bed Under Low Flow Conditions

Abstract

Turbulence is a fundamental aspect of natural river systems, significantly influencing sediment transport, channel morphology, and ecological habitats. In the channel bed, turbulence arises from the intricate interactions between flowing water and the diverse features of the riverbed. These interactions create a highly variable flow regime, characterized by vortices and eddies of different scales that profoundly affect the movement and distribution of sediments. Understanding the role of turbulence in a sediment bed open channel flow is crucial for several reasons. Firstly, turbulence directly impacts sediment transport processes, including erosion, deposition, and re-suspension of sediment particles. These processes shape the channel bed morphology over time, affecting the stability and dynamics of the channel. Secondly, sediment bed variations occur not only in the longitudinal direction but also transversely, influenced by factors such as wall shear stress and secondary currents. To address these issues, laboratory experiments were conducted in a sediment bed unsymmetrical compound channel at the Fluid Mechanics and Hydraulic Laboratory of the National Institute of Technology, Rourkela (NITR). A SonTek 16MHz ADV with a down-looking probe was used to measure the velocity fluctuations. The average velocity was estimated along with various turbulence parameters, including Reynolds shear stress, turbulent intensities, and turbulent kinetic energy. To deepen the understanding of bed morphology, sediment sorting downstream in the flume was examined. Results show that turbulence parameters vary both longitudinally and transversely. Longitudinally, turbulence parameters decrease due to downstream fining. Transversely, the parameters vary due to the effect of the channel wall and the junction part of the main channel and flood plain. These findings enhance the knowledge of turbulence effects on sediment transport and river morphology.