This paper reviews the problem of the incipient motion of cohesionless particles in a high sloping water stream. A theoretical analysis of the equilibrium of a gravel particle is developed by a deterministic approach with the introduction of the relative degree of exposure of the particle itself to the stream flow. The parameter, relative degree of exposure, relates the positioning of a particle with the upstream one. The problem of velocity distribution and the definition of drag coefficient is also revised to better account for low submergence. The results of the theory are compared with a series of ad hoc experiments performed by C. Gregoretti.