Sheet flow sand transport processes in oscillatory flow with acceleration skewness

Waves in the surf zone are characterised by their forward-leaning sawtooth shape, which leads to stronger acceleration and higher net sand transport in the onshore direction compared to the offshore direction. Present understanding of acceleration effects on sand transport is poor due to a lack of measurements of the detailed processes. The paper reports new large-scale oscillatory flow tunnel experiments with sawtooth-shaped flows over a fine sand bed under sheet flow conditions. Sand concentrations and velocities were measured using CCMs and PIV respectively. Results are presented showing concentration and velocity measurements extending deep into the sheet flow layer and intra-wave erosion depth, sheet flow layer thickness and flux. The significant effect of acceleration skewness is seen in all of the results.