Abstract
Entrainment of river bed particles by turbulent flow is a core matter of study in river hydrodynamics. It is of great interest to river engineers to evaluate the shear stress for initiating river bed motion. The main objective is to calculate transport rates for bed load, to predict changes in bed level which are scoured or aggraded and to design a stable channel. Forces acting upon the particle especially fluid forces which give a major role in the incipient motion of the particle on the rough boundary. For calculation generally use shield’s diagram but some other modified methods and approaches are discussed. Modeling criteria are discussed for the hydraulically smooth and rough boundary depending on Reynolds number. In the past, experimental studies on tractive shear stress have been done by many researchers but consideration of lift force to analyze the movement of sediment is very limited. For suspended load transport, a detailed analysis of lift force is required. Based on the study it has been observed that shear stress depends on channel slope not only due to gravitational force but also many other factors like drag force, lift force, friction angle, fluctuations, velocity profile, etc. Complete analysis of these factors provides slope dependency over shear stress. To improve past studies, some factors have been discussed, to give a more correct force balance equation. This is very difficult task to analyze more and more variable’s dependency on the slope. Consideration of the possible number of variable holds complete analysis of experimental study. This paper also reviews the effect of particle Reynolds number and relative submergence over critical shield stress. Doi: 10.28991/cej-2021-03091700 Full Text: PDF
Highlights
There is the most important problem in the transport mechanism of the sediment is the estimation of the flow intensity at which the movement of the sediment starts
According to the literature review and experiments made on the flume and Natural River or any stream for slope dependency, it has been observed that shield stress increases while increasing the slope of the bed
This paper reviewed the analysis of threshold motion of particle given by many authors through laboratory and field data to measure the critical tractive stress.To find the shear stress by Shield’s approach is implicit log-log plot approach.Due to implicity, it makes many applications complex and inconvenient.So there is more required to make the explicit formulation of shields parameter [78]
Summary
There is the most important problem in the transport mechanism of the sediment is the estimation of the flow intensity at which the movement of the sediment starts. This movement of the grain particles is achieved at a critical level where shear stress is such that it will start the motion. This shear is called critical tractive bed shear stress. Forces on bed particle: If the average tractive bed shear stress is not able to move the bed particles, the grains or river bed will be on rest. There are 3 main types of forces acting on the particle: Vol 7, No 05, May, 2021
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