Diffraction

Diffraction is the lateral spreading of wave energy into the geometric shadow behind an obstacle such as a breakwater tip, island, or harbor entrance. Because energy flows along the crest, waves do not simply stop at the barrier; the crest bends around the end and propagates into the lee with reduced height set by the diffraction coefficient, the ratio of sheltered to incident wave height. It is distinct from refraction, which is depth-driven, though both reshape the crest. Harbor agitation studies use diffraction diagrams (or combined refraction-diffraction models) to size breakwaters and predict wave heights at berths inside a partly sheltered basin.