In the present work the lateral particles dispersion of the bed load transport in open channel with rough bed is studied theoretically using the 3D numerical model of the spherical particle saltation, i.e. the main mode of the bed load transport. The particle lateral deviation from the flow direction has a random character, it occurs mainly due to the particle-bed collisions. The aim of the study is to estimate the value of particle deviation from the downstream direction. The main results of the work are: 1)the saltating particle due to collision with the rough bed could deviate from the downstream direction on a distance, which standard deviation is proportional to the square root of the distance passed by the particle along the downstream direction; 2)the saltating particle is on the given distance from the downstream direction with the probability, which distribution function keeps similar along the downstream direction.
