Edge-wave-driven durable variations in the thickness of the surfactant film and concentration of surface floats

• Trains of linear edge waves create a quasi-periodic pattern of deviations of the thickness of the surfactant film.
• No durable changes in the thickness occur owing to such trains.
• Focusing of linear edge waves may lead to durable changes in the thickness of the surfactant film.
• Such focusing may lead to the formation of patches of debris or litter at sea surface.

By employing a simple model for small-scale linear edge waves propagating along a homogeneous sloping beach, we demonstrate that certain combinations of linear wave components may lead to durable changes in the thickness of the surfactant film, equivalently, in the concentration of various substances (debris, litter) floating on the water surface. Such changes are caused by high-amplitude transient elevations that resemble rogue waves and occur during dispersive focusing of wave fields with a continuous spectrum. This process can be treated as an intrinsic mechanism of production of patches in the surface layer of an otherwise homogeneous coastal environment impacted by linear edge waves.