High-order structure functions are applied at the particle scale for studying water-worked gravel surfaces measured at several field sites in New Zealand. The key findings relate to the shape of the two-dimensional structure functions and their scaling behavior. The data suggest that at scales comparable to d50 the topography of gravel surfaces is sensitive to the flow direction and exhibits multiscaling behavior. We postulate, based on our analysis and physical considerations, that the high-order structure functions may provide information on the orientation and direction of the flow that formed the surface.