Scaling law governing the roughness of the swash edge line

The physics of swash i.e. a layer of water that washes up on the beach after an incoming wave has broken is complicated and intriguing. It includes perplexed hydrodynamic and sediment transport events. In our paper we address to the roughness of the moving swash boundary at which a beach, water and air meet. We treat the behavior of this boundary as an interfacial phenomenon, without going into details of formation of edge waves and beach cusps, covered broadly in literature. This "crude" approach turns out to be productive and revealing the resemblance of the swash line with a broad diversity of effects arising from the random pinning of moving boundaries.