The entrainment of sediments by the turbulent flow of water

Abstract

This paper attempts to clarify the role of fluid turbulence in the entrainment process of particles from the flat bed of an alluvial channel. A 6 mm diameter sphere, placed in an array of similar particles on the bed of a laboratory flume, was connected to a 3-component force transducer. Dynamic measurements of longitudinal, lift and lateral force components were made with the particle at a number of positions above the bed. Detailed measurements of velocity and turbulence were also made. The velocity and force spectral measurements showed similarities in the longitudinal (streamwise) direction but the lift force component spectra were significantly different.

An analytical model of the entrainment process is proposed, in which the impulse required to lift a sediment particle from the channel bed may be calculated. The experimental data has been used to evaluate the constants in the analytical expressions, and a relationship between the forces and turbulence intensity established. The analysis shows that the impulse required to entrain a particle may be expressed as a function of a dimensionless entrainment parameter, the turbulence intensity, and the initial angle of repose of the particle.