Edge Wave

An edge wave is a wave trapped against a sloping coast, propagating alongshore with its amplitude largest at the shoreline and decaying seaward across a few wavelengths. Refraction over the beach slope reflects the wave energy back toward shore and confines it, so the wave runs parallel to the coast as a standing or progressive mode. Edge waves carry discrete modes (mode 0, 1, 2) with frequencies set by the beach slope, and they couple to incident swell at sub-harmonic and infragravity periods. They organize rip-current spacing and the rhythmic cusps and crescentic bars seen on many beaches, and they reinforce wave setup at the shoreline.