Water Waves - Wave Formation

Wave Formation

The great majority of large breakers one observes on a beach result from distant winds. Five factors influence the formation of wind waves:

• Wind speed
• Distance of open water that the wind has blown over (called the fetch)
• Width of area affected by fetch
• Time duration the wind has blown over a given area
• Water depth

All of these factors work together to determine the size of wind waves. The greater each of the variables, the larger the waves. Waves are characterized by:

• Wave height (from trough to crest)
• Wavelength (from crest to crest)
• Wave period (time interval between arrival of consecutive crests at a stationary point)
• Wave propagation direction

Waves in a given area typically have a range of heights. For weather reporting and for scientific analysis of wind wave statistics, their characteristic height over a period of time is usually expressed as significant wave height. This figure represents an average height of the highest one-third of the waves in a given time period (usually chosen somewhere in the range from 20 minutes to twelve hours), or in a specific wave or storm system. The significant wave height is also the value a "trained observer" (e.g. from a ship's crew) would estimate from visual observation of a sea state. Given the variability of wave height, the largest individual waves are likely to be somewhat less than twice the reported significant wave height for a particular day or storm.