Inception of gravel bed motion beneath tidal bores: an experimental study

Abstract: A tidal bore is a positive surge taking place during the flood tide under macro-tidal conditions and the bore represents the leading edge of the tidal wave propagating upstream. The fundamentals of tidal bores remain unknown, although some physical experiments were performed during the last two decades. In this study, some physical modelling was performed to investigate the tidal bore propagation and turbulent mixing on fixed and movable gravel beds with both undular and breaking bores. Further observations of particle motion beneath the bore front were recorded. The results showed the significant impact of breaking bore propagation on the gravel bed motion, associated with upstream gravel bed load motion behind the bore. The gravel bed particles were destabilised by the roller toe passage and advected upstream with a convective velocity about 1/7th of the bore celerity.