A tidal bore may develop in an estuary during the spring tide conditions when the tidal range exceeds 5-6 m and the flood tide is confined to a narrow funnelled estuary with low freshwater levels. The tidal bore is of great importance for the geomorphology of the estuarine zone. In this study, some physical modelling was performed to investigate the sediment motion inception beneath a tidal bore on a movable gravel bed. The results show the significant impact of breaking bore propagation on the gravel bed motion. The dominant contribution to sediment transport inception is the longitudinal pressure gradient force, while the transient recirculation motion next to the bed yields to a drag force acting in the upstream direction and contributing to sediment motion. (C) 2012 Elsevier Ltd. All rights reserved.