Refraction and reflection of infragravity waves near submarine canyons

The propagation of infragravity waves (ocean surface waves with periods from 20 to 200 s) over complex inner shelf (water depths from about 3 to 50 m) bathymetry is investigated with field observations from the southern California coast. A wave‐ray‐path‐based model is used to describe radiation from adjacent beaches, refraction over slopes (smooth changes in bathymetry), and partial reflection from submarine canyons (sharp changes in bathymetry). In both the field observations and the model simulations the importance of the canyons depends on the directional spectrum of the infragravity wave field radiating from the shoreline and on the distance from the canyons. Averaged over the wide range of conditions observed, a refraction‐only model has reduced skill near the abrupt bathymetry, whereas a combined refraction and reflection model accurately describes the distribution of infragravity wave energy on the inner shelf, including the localized effects of steep‐walled submarine canyons.