Glenn Wolff L ike waves of light, water waves can be diffracted, reflected, and refracted when they encounter stationary objects or shoreline features. In diffraction, waves bend around a barrier such as a jetty or sandbar, producing smaller waves behind it. It explains why small islands in mid-ocean have no protected shore. Heavy surf will pound even their lee side, making it difficult to land boats.
Waves reflect when they meet upright jetties, seawalls, or other vertical walls.
Reflected waves rebound back into the path of oncoming waves, sometimes reinforcing an advancing wave and making it larger. They might also meet oncoming waves and halt them, turning them into standing waves that move up and down but make no horizontal progress. If waves meet a barrier at an angle they are reflected away at the same angle. When a wave meets a beach most of its energy is absorbed, but there is always some reflection. Refraction occurs when waves are bent by shallow water.