FLOW CHARACTERISTICS OF EQUILIBRIUM AND NON-EQUILIBRIUM SEDIMENT TRANSPORT FLOWS

Abstract

Sediment transport in a river segment can be in equilibrium or non-equilibrium, depending on the amount of sediment entering and leaving the segment. The sediment transport flow can cause the riverbed to either remain stable or become unstable, resulting in either degradation or aggradation of the riverbed. This study evaluates the effect of equilibrium and non-equilibrium sediment transport on flow characteristics such as velocity, turbulence intensity, and Reynolds shear stress. Experiments were conducted with (SF) and without sediment feeding (NSF) to represent the laboratory's two sediment transport conditions. One hundred and twenty mean velocity and turbulence profiles were measured using an Acoustic Doppler Velocimeter in movable bed flows with sediment transport. The flow velocity profile with sediment feeding tends to become more slender than that without sediment feeding. The velocity profile in the inner region decreases and increases in the outer region. The friction velocity, u_*, and the integration constant of the logarithmic law, Br, which decreases closer to the channel side wall, show a more pronounced trend for the data with sediment feeding. The data on turbulence intensities of u’/u_*, v’/u_*, w’/u_*, follows an exponential law pattern; clear distinctions are observed between flows with and without sediment feeding. The measurement of Reynolds shear stress -u_fv_f/u_*²   displays a linear trend of shear-stress distribution. The suppression of Reynolds shear stress is observed and is more pronounced closer to the channel bed (y/H < 0.15 – 0.2) and towards the channel side wall, especially for the flow with sediment feeding.