Diffusion of saltating particles in unidirectional water flow over a rough granular bed

We show that the motion of saltating particles on a flat rough bed in unidirectional water flow is diffusive and comprises three ranges (local, intermediate, and global) of spatial and temporal scales with different scaling behaviour and diffusion properties. Our computer simulations suggest that the ratio of the travelling particle diameter to the prevailing diameter of static bed particles (or the height of bed roughness) is one of the key parameters controlling particle diffusion.