Assessment of existing sediment transport models for sand barrier dynamics under waves & currents

Abstract

The paper summarizes morphology changes over rippled sand barriers under wave and wave combined current of 27 laboratorial experiments. Data of 4 wave conditions (H=10cm, T=1s; H=12cm, T=1s; H=12cm, T=1.5s; H=14cm, T=1.5s) and 6 currents (Q= 10, -10, 20, -20, 25, -25 l/s) including 4 cases of wave only were analysed. Sediment transport direction of the shorter period wave combinations is opposite to the current direction. In other words, qs is against wave propagation when waves and current are in the same direction; while qs is in the wave propagation direction when the waves propagate against the current. The qs-direction of sediment transport is not consistent in the combinations of longer period wave. The existing sediment transport formulae in a wave-current induced ripple bed morphology are assessed utilizing available laboratory data of wave, velocity, bed change and ripple dimensions. Five models work well and are widely used in non-breaking waves over rippled beds such as the diffusion model, the heuristic model, the grab and dump model of Nielsen (1988), Ribberink & Al-Salem (1994) and Nielsen‟s (2006) were tested against experimental data. The results illustrate the challenges related to complicated vertical velocity distributions in combined wave-current flows and the relations between near-bed fluid velocities and sediment transport rates, even in 2DV flows.