Wind waves in the context of "Ambient noise"

A swell, also sometimes referred to as ground swell, in the context of an ocean, sea or lake, is a series of mechanical waves that propagate along the interface between water and air under the predominating influence of gravity, and thus are often referred to as surface gravity waves. These surface gravity waves have their origin as wind waves, but are the consequence of dispersion of wind waves from distant weather systems, where wind blows for a duration of time over a fetch of water, and these waves move out from the source area at speeds that are a function of wave period and length. More generally, a swell consists of wind-generated waves that are not greatly affected by the local wind at that time. Swell waves often have a relatively long wavelength, as short wavelength waves carry less energy and dissipate faster, but this varies due to the size, strength, and duration of the weather system responsible for the swell and the size of the water body, and varies from event to event, and from the same event, over time. Occasionally, swells that are longer than 700 m occur as a result of the most severe storms.

Swell direction is the direction from which the swell is moving. It is given as a geographical direction, either in degrees, or in points of the compass, such as NNW or SW swell, and like winds, the direction given is generally the direction the swell is coming from. Swells have a narrower range of frequencies and directions than locally generated wind waves, because they have dispersed from their generation area and over time tend to sort by speed of propagation with the faster waves passing a distant point first. Swells take on a more defined shape and direction and are less random than locally generated wind waves.

Wave overtopping is the time-averaged amount of water that is discharged (in liters per second) per structure length (in meters) by waves over a structure such as a breakwater, revetment or dike which has a crest height above still water level.

When waves break over a dike, it causes water to flow onto the land behind it. Excessive overtopping is undesirable because it can compromise the integrity of the structure or result in a safety hazard, particularly when the structure is in an area where people, infrastructure or vehicles are present, such as in the case of a dike fronting an esplanade or densely populated area.

The riding of waves has likely existed since humans began swimming in the ocean. In this sense, bodysurfing is the oldest type of wave-catching. Undoubtedly ancient sailors learned how to ride wave energy on many styles of early boats. Archaeological evidence even suggests that ancient cultures of Peru surfed on reed watercraft for fishing and recreation up to five thousand years ago. However, standing up on what is now called a surfboard is a relatively recent innovation developed by the Polynesians. The influences for modern surfing can be directly traced to the surfers of pre-contact Hawaii.