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Glossary of Some Terms Related to Rip Currents
Backwash: The seaward return of the water following the uprush of the waves. Also called backrush or run down.
Breaker: A wave that has become so steep that the crest of the wave topples forward, moving faster than the main body of the wave.
Breaker zone: The zone within which waves approaching the coastline commence breaking, typically in water depths of between 5 m and 10 m.
Embayment: An indentation in a shoreline forming an open bay.
Groin: A shore-protection structure (built usually to trap littoral drift or retard erosion of the shore). It is narrow in width (measured parallel to the shore) and its length may vary from tens to hundreds of meters (extending from a point landward of the shoreline out into the water). Groins may be classified as permeable (with openings through them) or impermeable (a solid or nearly solid structure).
Head of a rip: That part of a rip current circulation typically located beyond the breakers, marked by a spreading out or fanning of the circulation. It is here where the velocity and strength of the rip current circulation begins to weaken considerably.
Rip Channel: A channel cut by the seaward flow of a rip current, usually crossing a sandbar.
Rip current: A relatively small-scale surf-zone current moving away from the beach. Rip currents form as waves disperse along the beach causing water to become trapped between the beach and a sandbar or other underwater feature. The water converges into a narrow, river-like channel moving away from the shore at high speed. A rip current consists of three parts: the feeder current flowing parallel to the shore inside the breakers; the neck, where the feeder currents converge and flow through the breakers in a narrow band or "rip"; and the head, where the current widens and slackens outside the breaker line.
Run-up: the rush of water up a beach due to the breaking of a wave. The amount of run-up is the vertical height above stillwater level that the rush of water reaches.
Sand bar: An offshore ridge or mound which is submerged (at least at high tide), especially at the mouth of a river or estuary, or lying parallel to, and a short distance from, the beach.
Shoreline : The intersection of the ocean water surface with the shore or beach.
Significant Wave Height: The average wave height of the one-third highest waves of a given wave group.
Surf Zone: Area of water between the high tide level on the beach and the seaward side of breaking waves.
Swell: Wind-generated waves that have traveled out of their source region, usually over a considerable distance. Swell waves exhibit a more regular and longer period with flatter crests than choppy, locally generated wind waves.
Tide: The periodic rising and falling of the water which results from gravitational attraction of the Moon and Sun acting upon the rotating Earth.
Undertow: There is spirited discussion and disagreement among coastal scientists on the existence of a nearshore process called "undertow," and hence there is not an agreed on definition for this word. Undertow is a term often and incorrectly used for rip currents. The best explanation for what many people attribute to "undertow" is as follows: After a wave breaks and runs up the beach, most of the water flows seaward; this "backwash" of water can trip waders, move them seaward, and make them susceptible to immersion from the next incoming wave; however, there is no surf zone force that pulls people under the water.
Wave Height: The vertical distance between the crest and the preceding trough of a wave.
Wind Waves: Waves generated by, and directly attributable to local winds, as opposed to swell waves, which have traveled over a considerable distance and produced by winds occurring at some previous time.
|Last Updated: July 7, 2005|