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Glossary of Some Terms Related to Rip Currents

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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.

Cusp: One of a series of short ridges on the shore separated by crescent-shaped troughs spaced at more or less regular intervals. Between these cusps are hollows. The cusps are spaced at somewhat uniform distances along beaches. They represJuly 7, 2005.

Embayment: An indentation in a shoreline forming an open bay.

Estuary:

  • A semi-enclosed coastal body of water which has a free connection with the open sea. The seawater is usually measurably diluted with freshwater.
  • The part of the river that is affected by tides.
  • The zone or area of water in which freshwater and saltwater mingle and water is usually brackish due to daily mixing
    and layering of fresh and salt water.

Feeder current: The currents which flow parallel to shore before converging and forming the neck of a rip current.

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.

Jetty: On open seacoasts, a structure extending into a body of water to direct and confine the stream or tidal flow to a selected channel, or to prevent shoaling. Jetties are built at the mouth of a river or entrance to a bay to help deepen and stabilize a channel and facilitate navigation.

Littoral currents: A current running parallel to the beach and generally caused by waves striking the shore at an angle.

Littoral drift: The sedimentary material moved parallel to the shoreline in the nearshore zone by waves and currents.

Longshore current: A current located in the surf zone, moving generally parallel to the shoreline, generated by waves breaking at an angle with the shoreline, also called the alongshore current.

Neck: That part of a rip current circulation located in the surf zone, marked by a narrow band of swiftly moving, seaward flowing water. It is here where velocity of the circulation is at a maximum, and where most rip current drowning deaths occur.

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.

Rip Tide:  Rip currents are not rip tides. A distinctly separate type of current includes both ebb and flood tidal currents that are caused by egress and ingress of the tide through inlets and the mouths of estuaries, embayments and harbors. These currents may cause drowning deaths, but these tidal currents or jets are a separate and distinct phenomenon from rip currents. Recommended terms for this phenomenon
include ebb jet or tidal jet.

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.

Definitions taken from National Weather Service Directives System,  NOAA Coastal Services Center and National Weather Service Rip Current Technical Team

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Last Updated: July 7, 2005