Edge waves along a sloping beach

Standing on a gently sloping straight beach, it is a matter of observation that various waveforms propagate on the surface of the sea. Among these we find edge waves water waves that progress along the shoreline. These waves, often difficult to visualize (this has, probably, prevented the regarding of this waveform as important for a long time), are coastal trapped, i.e. their amplitude is maximal at the shoreline and decays rapidly offshore. They produce on the beach beautiful run-up patterns (highest points reached by a wave on the beach). Although propagation is along the straight shoreline and the waveform is sinusoidal in the longshore, these waves are not one-dimensional (Lighthill 1978). While they were originally considered to be a curiosity (Lamb 1932), edge waves are now recognized to play a significant role in nearshore hydrodynamics. For shallow beaches empirical evidence shows that incident storm waves loose most of their energy trough wave breaking by the time they reach the shore. After breaking offshore, as the waves progress to shallower water, their height decreases reaching its least value at the shoreline. Since storms often result in pronounced shoreline erosion, the surf zone water processes with the onset of a storm are dominated by wave conditions other than the incident waves role attributed by oceanographers to the edge waves ; see Komar (1998). There are other instances when edge waves are of significance. For example, processed data from the water waves created by an earthquake occuring in April 1992 in the ocean floor near the Californian coast show that two distinct wave packets (both directly generated in the nearshore by the vertical motion of the ocean bottom)