Under storm conditions, the majority of sand on the upper shoreface is transported in the sheet-flow layer, only a few em's thick. Existing sand transport models are primarily based on data from oscillatory flow tunnel experiments. This paper addresses the importance of surface wave effects on sheet-flow sand transport, which are not fully reproduced in tunnels. A comparison is made between the velocity behaviour under full-scale surface waves and comparable tunnel experiments, and the impact of this on sediment transport rates is explored. New velocity measurements under full-scale surface waves, as well as process-based I DV model simulations are used to address these issues. This paper shows that the net velocities under real waves and in tunnels differ strongly, which has a large influence on the net current-related transport rates inside the sheet-flow layer. How this relates to the corresponding wave-related transport should be investigated in further detail.