The difference between 'the equilibrium wave energy dissipation rate' and 'the wave energy dissipation rate' is incorporated in energy per unit of bed area that sediment particles should bear in order to dislocate their position in forming the offshore bar. The result depicted average displacement of sediment particles while the beach profile morphologically changes under storm waves. Theoretical hypothesis is tested using series of experiments such that the volume of offshore bar and the fictive period for the time scale of sediment dislocation, under regular and irregular wave conditions, could be examined. Findings show that fall speed parameter and dimensionless depth parameter govern the average dislocation of sediment particles. (C) 2004 Elsevier Ltd. All rights reserved.