Flow and turbulence characteristics of bed load sediment transport for self-cleansing without deposition

Abstract

Investigating the structure of flow turbulence and bed load sediment transport is crucial as it provides insights into the functioning of aquatic environments, where such variations can lead to changes in ecosystem dynamics. This study focuses on the impact of sediments on the hydraulic characteristics of flow at self-cleansing without deposition conditions of sediment transport. The self-cleansing without deposition is not only a mode of sediment transport in alluvial channels, but it also serves as a criterion for the design of lined channels. Among the various design concepts for lined open channels, such as sewers and drainage channels, self-cleansing without deposition condition is implemented as the most conservative and reliable approach. However, most of the conducted experimental studies on self-cleansing without deposition have focused on measuring the basic flow and sediment characteristics for modelling purposes and neglected the effect of bed load, sediment size, flow discharge, and channel bed slope on turbulence characteristics. This study addresses this gap by examining the impact of bed load, sediment size, bed slope, and discharge on turbulence characteristics through a series of experiments conducted in a 12.5 m flume with a rectangular cross-section, equipped with an automatic control system (ACS) at the Hydraulic Laboratory of Ya & scedil;ar University. The channel bed slope, sediment discharge, flow discharge, and depth were adjusted and measured using ACS. Discharge and flow depth were measured using an ultrasonic flow-meter and depth sensors, respectively. Flow characteristics were measured using a Vectrino profiler device. The study reveals that bed load sediment transport reduces streamwise velocity, especially for coarse particles. Additionally, at a constant bed slope, velocity differences remain small at lower discharges but become more significant as discharge increases. Turbulence intensity rises with bed load motion, more in the streamwise direction than vertically. At a constant bed slope, increasing discharge enhances turbulence, but the effect is more pronounced at lower slopes and less significant at steeper slopes. Reynolds shear stress increases with particle size and steeper slopes, indicating greater shear production. These observations suggest critical implications for the design and optimization of open-channel systems, emphasizing the need for detailed consideration of particle sizes and bed conditions in engineering practices.