The energy of the waves

Between January 19 and 22, 2020, the storm Gloria hit the east coast of the Iberian Peninsula with an unusual severity. Torrential rains flooded a large part of the territory, and a strong east wind generated waves up to 15 meters high, which destroyed beaches and infrastructure throughout the coastline.
The waves are generated with the wind and depend on its speed, the time it blows and the fetch, or distance that travels above the surface of the water. Initially the waves are born as roughnesses known as capillary waves, but the action of gravity ends up turning them into very symmetrical sinusoidal oscillations. Its most important parameters are wavelength, height, amplitude and period. When they travel along the surface of the water they dissipate very little energy, therefore, they can travel hundreds of kilometers before crashing against the coast, reaching places far away in space and time, from the wind that generated them (swell). Waves can experience reflection, refraction and diffraction. Once they approach the coast they deform until they become unstable, break and release all the energy. This energy, when it is small, can have a constructive effect and contribute sediment to the beach, especially in summer, while if it is very large it has a destructive effect, especially in winter. The coastal dynamics is altered with the construction of ports and jets that hinder the longitudinal transport of sand and, consequently, the beaches recede.
A fun way to harness the energy of the waves is with surfing. This sport was born in the Hawaiian Islands, where Captain Cook’s crew already mention it in 1767. Today, it is well known and practiced throughout the world to the point that many waves have name and surname as Pipeline in Hawaii, Maveriks in California, Nazaré in Portugal or Mundaka in the Basque Country. Surfing a good wave is a brief pleasure, and difficult to achieve, hence the saying “one wave, makes a session”.