This is a simulation of monochromatic (17s), unidirectional (from 285 deg. T) wave crests propagating across the north (Scripps) canyon (black contour lines). Crests appear in red, troughs in blue. Refraction of wave energy away from the canyon axis results in low wave heights directly to the east of the canyon head. A wave crest that refracts back to the north of the canyon head interferes with the portion of the same crest that has stayed to the north of the canyon, producing complex interference patterns and high wave heights. More realistic random incident wave conditions do not completely mask these bathymetrically-induced interference patterns because the node and antinode locations change slowly with variations in the incident wave period and direction. In addition, the node and antinode locations are insensitive to the initial phase of the wave crest at the model's offshore boundary.

Spectral refraction-diffraction simulations produce smaller maximum wave heights north of the canyon, and larger minimum wave heights east of the canyon compared with spectral refraction simulations. One role of diffraction is to reduce the extremes (both high and low) of the wave field that would be produced by pure refraction of the incident spectra. Qualitative comparisons of spectral refraction-diffraction results with visual observations of wave heights north of the canyon (ie, feedback from surfers) suggests that the model underpredicts the high wave heights. One potential source of additional wave energy north of the canyon is (unmodeled) reflection from the steep canyon walls.

The official Refraction-Diffraction model source code can be obtained from Jim Kirby at http://chinacat.coastal.udel.edu/~kirby/programs/refdif.html.