Effects of sediment transport on bed friction and turbulence

The effects of sediment transport on the fluid velocities and turbulence in oscillatory flow were investigated with the aid of a laser Doppler anemometer (LDA). Measurements were made over flat beds in an oscillatory flow water tunnel with gradually increasing quantities of sediment. The sediment had a specific gravity of 1.137 and a median diameter of 4.0 mm. It was observed that the turbulence intensity at any given height above the initial bed level was less in flows with sediment motion than over a fixed bed provided the bed remained flat. The initial bed level is defined as the mean grain crest level if all sediment settles on the bed. The friction factor and energy dissipation factor at the initial bed level were also reduced by the addition of sediment provided the bed remained flat. On the other hand, the values of friction factor and energy dissipation factor at the bottom of the mobile layer of sediment were greater than the values for a fixed bed.