EFFECTS OF SEDIMENT TRANSPORT ON BED FRICTION AND TURBULENCE

The effects of sediment transport on the fluid velocities and turbulen ce in oscillatory flow were investigated with the aid of a laser Doppl er anemometer (LDA). Measurements were made over flat beds in an oscil latory flow water tunnel with gradually increasing quantities of sedim ent. The sediment had a specific gravity of 1.137 and a median diamete r of 4.0 mm. It was observed that the turbulence intensity at any give n height above the initial bed level was less in flows with sediment m otion than over a fixed bed provided the bed remained flat. The initia l bed level is defined as the mean grain crest level if all sediment s ettles on the bed. The friction factor and energy dissipation factor a t the initial bed level were also reduced by the addition of sediment provided the bed remained flat. On the other hand, the values of frict ion factor and energy dissipation factor at the bottom of the mobile l ayer of sediment were greater than the values for a fixed bed.