Near-bed particle motion over transitionally-rough bed

The motion of sediment particles over a transitionally-rough bed is studied experimentally using a real-time high-speed imaging system. Vertical distributions of the instantaneous flow velocities were measured using acoustic Doppler velocimetry. The sediment saltation trajectories and the associated velocity components were deciphered from the high-speed images using digital image processing techniques. Sediments of different sizes and specific weights were used for experimentation. Particles moving in both the rolling and the saltation regimes were tested. Stochastic deviations of the particle velocity, the particle acceleration and the angle of velocity vector orientation during its motion due to particle interactions with flow and the channel bed are quantified. The angle distributions and the acceleration fluctuations are approximately bell-shaped. Using the experimental data, a generalized single relation for particle velocity is proposed for saltation and rolling sediments. The results of particle m...