Rip current

A rip current, often simply called a rip (or misleadingly rip tide), is a specific kind of water current which can occur near beaches with breaking waves. A rip is a strong, localized, and narrow current of water which moves directly away from the shore, cutting through the lines of breaking waves like a river running out to sea, and is strongest near the surface of the water.[1]

Rip currents can be hazardous to people in the water. Swimmers who are caught in a rip current and who do not understand what is going on, and who may not have the necessary water skills, may panic, or exhaust themselves by trying to swim directly against the flow of water. Because of these factors, rips are the leading cause of rescues by lifeguards at beaches, and rips are the cause of an average of 46 deaths by drowning per year in the United States.

A rip current is not the same thing as undertow, although some people use the term incorrectly when they often mean a rip current. Contrary to popular belief, neither rip nor undertow can pull a person down and hold them under the water. A rip simply carries floating objects, including people, out beyond the zone of the breaking waves.

Rip current warning signs at Mission Beach
Rip current warning signs posted in English and Spanish at Mission Beach, San Diego, California
Backcomp
Workings of a rip current viewed from above: breaking waves cross a sand bar off the shore. The pushed-in water can most easily travel back out to sea through a gap in the sand bar. This creates a fast-moving rip current.

Causes and occurrence

A rip current forms because wind and breaking waves push surface water towards the land, and this causes a slight rise in the water level along the shore. This excess water will tend to flow back to the open water via the route of least resistance. When there is a local area which is slightly deeper, or a break in an offshore sand bar or reef, this can allow water to flow offshore more easily, and this will initiate a rip current through that gap.

Water that has been pushed up near the beach flows along the shore towards the outgoing rip as "feeder currents", and then the excess water flows out at a right angle to the beach, in a tight current called the "neck" of the rip. The "neck" is where the flow is most rapid. When the water in the rip current reaches outside of the lines of breaking waves, the flow disperses sideways, loses power, and dissipates in what is known as the "head" of the rip.

Rip currents can often occur on a gradually shelving shore where breaking waves approach the shore parallel to it, or where underwater topography encourages outflow at a specific area. Rip currents can form at the coasts of oceans, seas, and large lakes, whenever there are waves of sufficient energy. The location of rip currents can be difficult to predict; whereas some tend to recur always in the same places, others can appear and disappear suddenly at various locations along the beach. The appearance and disappearance of rip currents is dependent on the bottom topography and the exact direction that the surf and swells are coming in from.[2]

Rip currents can potentially occur wherever there is strong longshore variability in wave breaking. This variability may be caused by such features as sandbars (as shown in the animated diagram), by piers and jetties, and even by crossing wave trains, and are often located in places such as where there is a gap in a reef or low area on a sandbar. Rip currents may deepen the channel through a sandbar once they have formed.

Rip currents are usually quite narrow, but tend to be more common, wider, and faster, when and where breaking waves are large and powerful. Local underwater topography makes some beaches more likely to have rip currents; a few beaches are notorious in this respect.[3]

Although rip tide is a misnomer, in areas of significant tidal range, rip currents may only occur at certain stages of the tide, when the water is shallow enough to cause the waves to break over a sand bar, but deep enough for the broken wave to flow over the bar. (In parts of the world with a big difference between high tide and low tide, and where the shoreline shelves gently, the distance between a bar and the shoreline may vary from a few meters to a kilometer or more, depending whether it is high tide or low tide.)

A fairly common misconception is that rip currents can pull a swimmer down, under the surface of the water. This is not true, and in reality a rip current is strongest close to the surface, as the flow near the bottom is slowed by friction.

The surface of a rip current may appear to be a relatively smooth area of water, without any breaking waves, and this deceptive appearance may cause some beach goers to believe it is a suitable place to enter the water.[4]

Technical explanation

A more detailed description involves radiation stress. This is the force (or momentum flux) exerted on the water column by the presence of the wave. As a wave shoals and increases in height prior to breaking, radiation stress increases. To balance this, the local mean surface level (the water level with the wave averaged out) drops; this is known as setdown. As the wave breaks and continues to reduce in height, the radiation stress decreases. To balance this force, the mean surface increases — this is known as setup. As a wave propagates over a sandbar with a gap (as shown in the lead image), the wave breaks on the bar, leading to setup. However, the part of the wave that propagates over the gap does not break, and thus setdown will continue. Thus, the mean surface over the bars is higher than that over the gap, and a strong flow issues outward through the gap.

Visible signs and characteristics

Rip current warning signs
Some man-made signs warning of rip currents.
Ripcurrent viewed sideway
Disruption in the line of a breaking wave makes a rip current visible.

Rip currents have a characteristic appearance, and, with some experience, they can be visually identified from the shore before entering the water. This is useful to lifeguards, swimmers, surfers, boaters, divers and other water users, who may need to avoid a rip, or in some cases make use of the current flow. Rip currents often look a bit like a road or a river running straight out to sea, and are easiest to notice and identify when the zone of breaking waves is viewed from a high vantage point. The following are some characteristics that can be used to visually identify a rip:[5]

  • A noticeable break in the pattern of the waves — the water often looks flat at the rip, in contrast to the lines of breaking waves on either side of the rip.
  • A "river" of foam — the surface of the rip sometimes looks foamy, because the current is carrying foam from the surf out to open water.
  • Different color — the rip may differ in color from the surrounding water; it is often more opaque, cloudier, or muddier, and so, depending on the angle of the sun, the rip may show as darker or lighter than the surrounding water.
  • It is sometimes possible to see that foam or floating debris on the surface of the rip is moving out, away from the shore. In contrast, in the surrounding areas of breaking waves, floating objects are being pushed towards the shore.

These characteristics are helpful in learning to recognize and understand the nature of rip currents so that a person can recognize the presence of rips before entering the water. In the United States, some beaches have signs created by the National Oceanic and Atmospheric Administration (NOAA) and United States Lifesaving Association, explaining what a rip current is and how to escape one. These signs are titled, "Rip Currents; Break the Grip of the Rip".[6] Beachgoers can get information from lifeguards, who are always watching for rip currents, and who will move their safety flags so that swimmers can avoid rips.

Danger to swimmers

Hanakapiai Beach Warning Sign Only
Warning sign on the trail to Hanakapiai Beach, Hawaii.

Rip currents are a potential source of danger for people in shallow water with breaking waves in seas, oceans and lakes.[5] Rip currents are the proximate cause of 80% of rescues carried out by beach lifeguards.[7]

Rip currents typically flow at about 0.5 m/s (1.6 ft/s), but they can be as fast as 2.5 m/s (8.2 ft/s), which is faster than any human can swim. However, most rip currents are fairly narrow, and even the widest rip currents are not very wide; usually swimmers can exit the rip easily by swimming at a right angle to the flow, parallel to the beach. Swimmers who are unaware of this fact may exhaust themselves trying unsuccessfully to swim against the flow.[2] The flow of the current also fades out completely at the head of the rip, outside the zone of the breaking waves, so there is a definite limit to how far the swimmer will be taken out to sea by the flow of a rip current.

In a rip current, death by drowning occurs when a person has limited water skills and panics, or when a swimmer persists in trying to swim to shore against a strong rip current, thus eventually becoming exhausted and unable to stay afloat.

According to NOAA, over a 10-year average, rip currents cause 46 deaths annually in the United States, and 64 people died in rip currents in 2013.[8] However, the United States Lifesaving Association "estimates that the annual number of deaths due to rip currents on our nation's beaches exceeds 100."[6]

A study published in 2013 in Australia revealed that rips killed more people on Australian territory than bushfires, floods, cyclones and shark attacks combined.[9]

Management

Danger courant baines
A warning sign in France

People caught in a rip current may notice that they are moving away from the shore quite rapidly. It is often not possible to swim directly back to shore against a rip current, so this is not recommended. Contrary to popular misunderstanding, a rip does not pull a swimmer under the water, it simply carries the swimmer away from the shore in a narrow band of moving water.[1] The rip is like a moving treadmill, which the swimmer can get out of by swimming across the current, parallel to the shore, in either direction, until out of the rip current, which is usually not very wide. Once out of the rip, swimming back to shore is relatively easy in areas where waves are breaking and where floating objects and swimmers are being pushed towards the shore.[10]

As an alternative, swimmers who are caught in a strong rip can relax and go with the flow (either floating or treading water) until the current dissipates beyond the surf line, and then they can signal for help, or swim back through the surf diagonally away from the rip and towards the shore.[2]

It is necessary for coastal swimmers to understand the danger of rip currents, to learn how to recognize them and how to deal with them, and if possible to swim in only those areas where lifeguards are on duty.[5]

Uses

Experienced and knowledgeable water users, including surfers, body boarders, divers, surf lifesavers and kayakers, will sometimes use rip currents as a rapid and effortless means of transportation when they wish to get out beyond the breaking waves.[11]

See also

References

  1. ^ a b "Rip Current Characteristics". College of Earth, Ocean, and Environment, University of Delaware. Retrieved 16 January 2009.
  2. ^ a b c "Rip Currents". United States Lifesaving Association. Retrieved 8 July 2009.
  3. ^ "Rip currents at Ocean Beach are severe hazard for unwary, UC Berkeley expert warns". University of California, Berkeley. 23 May 2002. Retrieved 10 January 2018.
  4. ^ Don't get sucked in by the rip... on YouTube
  5. ^ a b c "Rip Currents Safety". U.S. National Weather Service. Retrieved 16 January 2009.
  6. ^ a b "NOAA Reminds Swimmers That Rip Currents Can Be a Threat. Rip Current Awareness Week Is June 1–7, 2008" (Press release). National Oceanic and Atmospheric Administration. 2 June 2008. Retrieved 16 July 2014.
  7. ^ "NWS Rip Current Safety Home Page". U.S. National Weather Service. Retrieved 10 January 2018.
  8. ^ "NWS Weather Fatality, Injury and Damage Statistics". NOAA. 25 April 2018.
  9. ^ "Rips more deadly than bushfires and sharks". Australian Geographic. Retrieved 27 November 2013.
  10. ^ "Beach and Surf Safety". Science of the Surf. Retrieved 10 January 2018.
  11. ^ Cowan, C. L. "Ride the Rip". Paddling.com. Archived from the original on 17 August 2017. Retrieved 12 July 2018.

External links

2008 Atlantic hurricane season

The 2008 Atlantic hurricane season was the most disastrous Atlantic hurricane season since 2005, causing over 1,000 deaths and nearly $50 billion in damages. It was an above-average season, featuring sixteen named storms, eight of which became hurricanes, and five which further became major hurricanes, the highest number since the record-breaking 2005 season. It officially started on June 1 and ended on November 30. These dates conventionally delimit the period of each year when most tropical cyclones form in the Atlantic basin. However, the formation of Tropical Storm Arthur caused the season to start one day early. This season is the fifth most costly on record, behind only the 2004, 2005, 2012 and 2017 seasons, with over $49.5 billion in damage (2008 USD). It was the only year on record in which a major hurricane existed in every month from July through November in the North Atlantic.Bertha became the longest-lived July tropical cyclone on record for the basin, the first of several long-lived systems during 2008.

The season was devastating for Haiti, where over 800 people were killed by four consecutive tropical cyclones (Fay, Gustav, Hanna, and Ike), especially Hurricane Hanna, in August and September. Hurricane Paloma's outer rain bands also made landfall over Haiti. Ike was also the most destructive storm of the season, as well as the strongest in terms of minimum barometric pressure, devastating Cuba as a major hurricane and later making landfall near Galveston, Texas as a large high-end Category 2 hurricane. One very unusual feat was a streak of tropical cyclones affecting land. All but one system impacted land in 2008. The unprecedented number of storms with impact led to one of the deadliest and destructive seasons in the history of the Atlantic basin, especially with Ike, as its overall damages made it the second-costliest hurricane in the Atlantic at the time, although it would later drop to sixth after hurricanes Sandy, Harvey, Irma, and Maria.

Aireys Inlet

Aireys Inlet is a small coastal inlet and town located on the Great Ocean Road, southwest of Melbourne, Victoria, Australia. Aireys Inlet is located between Anglesea and Lorne, and joined with Fairhaven to the west.

Many surfers holiday in Aireys Inlet to take advantage of the popular Fairhaven beach. As the inclination of the beach can change dramatically between years, the surf is regarded as unpredictable. Swimmers should take note there is a strong rip current.

Painkalac Creek, which separates Aireys Inlet from Fairhaven, forms a salt lake or inlet behind the sand dunes before it cuts through to the ocean. Due to low water levels in the inlet it is not often that the inlet breaks through.

There is also a horseshoe-shaped reef at Step Beach which forms an excellent swimming hole at low tide. The towns main attraction, the Split Point Lighthouse overlooks the inlet. The lighthouse has made Aireys Inlet an icon along the Great Ocean Road.

Cross sea

A cross sea (also referred to as a squared sea or square waves) is a sea state of wind-generated ocean waves that form nonparallel wave systems. Cross seas have a large amount of directional spreading. This may occur when water waves from one weather system continue despite a shift in wind. Waves generated by the new wind run at an angle to the old.

Two weather systems that are far from each other may create a cross sea when the waves from the systems meet at a place far from either weather system. Until the older waves have dissipated, they create a perilous sea hazard.

This sea state is fairly common and a large percentage of ship accidents have been found to occur in this state. Vessels fare better against large waves when perpendicular to the waves. In a cross sea, vessels are more likely to be struck in a dangerous way.A cross swell is generated when the wave systems are longer-period swell, rather than short-period wind-generated waves.

Current (fluid)

A current in a fluid is the magnitude and direction of flow within that fluid. An air current presents the same properties specifically for a gaseous medium.

Types of fluid currents include

Boundary current

Current (stream), a current in a river or stream

Longshore current

Ocean current

Rip current

Rip tide

Subsurface currents

Turbidity current

Current (stream)

A current, in a river or stream, is the flow of water influenced by gravity as the water moves downhill to reduce its potential energy. The current varies spatially as well as temporally within the stream, dependent upon the flow volume of water, stream gradient, and channel geometry. In tidal zones, the current in rivers and streams may reverse on the flood tide before resuming on the ebb tide.

Dail Mòr

Dail Mòr (or Dalmore) is a hamlet situated in the Northside of Carloway, a major settlement on the Isle of Lewis in Scotland. The hamlet has a beach and a cemetery. A small well kept car park is available for visitors as are picnic & public BBQ facilities. The beach is a known surf destination mentioned in numerous guidebooks. Note there is a strong rip current at the north end of the beach.

Despite its remoteness, five of the six houses in the village were connected to fibre broadband in November 2012.In August 2016, the Transocean Winner oil rig ran aground, on a headland just off Dalmore beach. The oil rig was being towed from Norway to Malta, when it became detached from the tug boat.

Ed Dermer

Edmund Rupert Joseph "Ed" Dermer (born 30 October 1957) in Subiaco, Western Australia is an Australian politician. He is currently the member of the Western Australian Legislative Council representing the North Metropolitan Region. Elected to Parliament in the 1996 state election after the resignation of Samuel Mathew Piantadosi he is a member of the Labor Party.He was re-elected in the 2001 and 2005 state elections and has held the position of Government Whip in the Legislative Council from May 2001 to present.

Dermer was one of the three North Metropolitan Labor MLCs, along with Graham Giffard and Ken Travers, who proved to be critical in the introduction of Daylight saving in 2006 in Western Australia. Initially intending on voting against the motion, they all eventually decided to support the motion in line with the wishes of their electorate and party.In 2008, Dermer was caught in a rip current with his sons, Alexander and Cameron, at a Surfers Paradise beach. Dermer and Cameron had to be rescued by lifesavers. Shortly afterward he was diagnosed with a melanoma on the back of his neck, which was removed and found to be malignant.

Hanakapiai Beach

Hanakāpīʻai Beach is a beach in the Hawaiian islands located on Kauai's Nā Pali Coast. The beach is approximately 2 miles (3.2 km) from the start of the Kalalau Trail, a very popular hiking trail which is located at Keʻe Beach. It is also about 2 miles from Hanakapiai Falls. During summer months, Hanakāpīʻai Beach's sandy shore line is clearly visible; during winter months, dangerously powerful waves and high tides wash away the sandy shore line. The beach is remotely located with no road access. The word Hanakāpīʻai literally means "bay sprinkling food" in Hawaiian.

Hanakāpīʻai Beach is a popular tourist attraction; however, like many beaches on the Nā Pali Coast, strong rip currents, as well as high surf, dangerous shore breaks and other hazardous ocean conditions make Hanakāpīʻai Beach extremely dangerous. The Nā Pali Coast is especially treacherous because there are no major reefs to hinder potent ocean currents.

Kauai's geography makes Hanakāpīʻai conditions even more hazardous; in the event that one gets caught in a rip current (or otherwise swept out to sea) the nearest safe shore area is approximately six miles away. The currents in the region are so powerful that the bodies of at least 15 drowning victims have yet to be recovered. According to the local newspaper, from 1970 to 2010 about 30 people are known to have drowned here. Tourists often refer to a warning sign with 82 tally marks (as of August 2014) counting drowning victims. It has no official sponsor and this count is highly speculative.

Hurricane Irene (2005)

Hurricane Irene was a long-lived Cape Verde hurricane during the 2005 Atlantic hurricane season. The storm formed near Cape Verde on August 4 and crossed the Atlantic, turning northward around Bermuda before being absorbed by an extratropical cyclone while situated southeast of Newfoundland. Irene proved to be a difficult storm to forecast due to oscillations in strength. After almost dissipating on August 10, Irene peaked as a Category 2 hurricane on August 16. Irene persisted for 14 days as a tropical system, the longest duration of any storm of the 2005 season. It was the ninth named storm and fourth hurricane of the record-breaking season.

Although there were initial fears of a landfall in the United States due to uncertainty in predicting the storm's track, Hurricane Irene never approached land and caused no recorded damage; however, swells up to 8 ft (2.4 m) and strong rip currents resulted in one fatality in Long Beach, New York.

Hurricane Jose (2017)

Hurricane Jose was a powerful and erratic tropical cyclone which was the longest-lived Atlantic hurricane since Hurricane Nadine in 2012. Jose was the tenth named storm, fifth hurricane, and third major hurricane of the 2017 Atlantic hurricane season. Jose developed into a tropical storm on September 5 from a tropical wave that left the west coast of Africa nearly a week prior. A period of rapid intensification ensued on September 6, when Jose reached hurricane intensity. On September 8, it reached its peak intensity as a high-end Category 4 hurricane. However, due to wind shear, Jose weakened over the next few days as it completed an anti-cyclonic loop north of Hispaniola. Despite weakening to a tropical storm on September 14, Jose managed to regain hurricane intensity the next day as it began to curve northwards. Never strengthening above Category 1 status for the remainder of its lifespan, Jose degraded to a tropical storm once again on September 20. Two days later, Jose transitioned into a post-tropical cyclone as it drifted northeastwards off the coast of New England. By September 26, Jose's remnants dissipated off the East Coast of the United States.

Initially projected to impact the Antilles already affected by Hurricane Irma, Jose triggered evacuations in catastrophically damaged Barbuda, as well as in Saint Martin. Eventually, as Jose changed its path, its inner core and thus the strongest winds stayed offshore. Nonetheless, Jose still brought tropical storm-force winds to those islands. Later on, Jose brought heavy rain, swells, and rough surf to the East Coast of the United States, causing beach erosion and some flooding. A woman died after she was caught in a rip current in Asbury Park.

Hurricane Local Statement

A Hurricane Local Statement is a weather statement produced for the public by local Weather Forecast Offices of the National Weather Service in or near an area affected or forecast to be affected by a tropical storm or hurricane which provides an overview of the storm's local effects, including expected weather conditions, evacuation decisions made by local officials, and precautions necessary to protect life and property.These statements are meant to complement statements released by the National Hurricane Center, which is focused on regional effects of tropical storms & hurricanes. Hurricane local statements will generally provide a condensed version of storm information provided in NHC advisories, while expanding on the local impacts of the storm and actions made by local officials in response to the storm.According to the National Hurricane Center, local hurricane statements generally present the following:

A lead statement

A sentence detailing the counties, parishes, or cities covered by the statement

Watches and/or warnings in effect and the counties or parishes to which they apply

Recommended precautionary actions and the times they should be completed

Storm surge and storm tide information, including the times that various heights are expected, present heights, and their locations

Present winds and the expected time of onset of tropical storm or hurricane-force winds

Tornado, flood, flash flood, rip current, beach erosion, and inland high wind potential

The time of the next statement

Information on the probability of hurricane or tropical storm conditions may also be included. An example section of a hurricane local statement is provided below.

North Cronulla Beach

North Cronulla Beach or North Cronulla is a patrolled beach on Bate Bay, in Cronulla, New South Wales, Australia. The Wall is the local name given to the area between North Cronulla Beach and Elouera. The Alley is the local name given to the permanent rip current located at the southern end of North Cronulla Beach.

Rip current statement

A Rip current statement is issued by the National Weather Service of the United States when there is a high threat of rip currents due to weather and ocean conditions.

Rip tide

A riptide is a strong, offshore current that is caused by the tide pulling water through an inlet along a barrier beach, at a lagoon or inland marina where tide water flows steadily out to sea during ebb tide. It is a strong tidal flow of water within estuaries and other enclosed tidal areas. The riptides become the strongest where the flow is constricted. When there is a falling or ebbing tide, the outflow water is strongly flowing through an inlet toward the sea, especially once stabilized by jetties. During these falling and ebbing tides, a riptide can carry a person far offshore. For example, the ebbing tide at Shinnecock Inlet in Southampton, New York, extends more than 300 metres (980 ft) offshore. Because of this, riptides are typically more powerful than rip currents.

During slack tide, the water is motionless for a short period of time until the flooding or rising tide starts pushing the sea water landward through the inlet. Riptides also occur at constricted areas in bays and lagoons where there are no waves near an inlet.

These strong, reversing currents can also be termed ebb jets, flood jet, or tidal jets by coastal engineers because they carry large quantities of sand outward that form sandbars far out in the ocean or into the bay outside the inlet channel. The term "ebb jet" would be used for a tidal current leaving an enclosed tidal area, and "flood jet" for the equivalent tidal current entering it.

The term "rip tide" or "riptide" is often incorrectly applied to rip currents, which are not tidal flows. A rip current is a strong, narrow jet of water that moves away from the beach and into the ocean as a result of local wave action. They can flow quickly, are unpredictable and are a result of the shape of the coastline. Instead, a rip tide is caused by the Moon's gravitational pull and is a predictable rise and fall of the water level.The United States National Oceanic and Atmospheric Administration (NOAA) comments:

Rip currents are not rip tides. A specific type of current associated with tides may include both the 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 tidal jets are separate and distinct phenomena from rip currents. Recommended terms for these phenomena include ebb jet, flood jet, or tidal jet.

Riptide (disambiguation)

Rip tide is a strong tidal flow of water within estuaries and other enclosed tidal areas.

Riptide or rip tide may also refer to:

A common misnomer for a rip current, a fast narrow current running offshore and cutting through breaking waves

Surf zone

As ocean surface waves come closer to shore they break, forming the foamy, bubbly surface called surf. The region of breaking waves defines the surf zone. After breaking in the surf zone, the waves (now reduced in height) continue to move in, and they run up onto the sloping front of the beach, forming an uprush of water called swash. The water then runs back again as backswash. The nearshore zone where wave water comes onto the beach is the surf zone. The water in the surf zone, or breaker zone, is shallow, usually between 5 and 10 m (16 and 33 ft) deep; this causes the waves to be unstable.

Surfing

Surfing is a surface water sport in which the wave rider, referred to as a surfer, rides on the forward or face of a moving wave, which usually carries the surfer towards the shore. Waves suitable for surfing are primarily found in the ocean, but can also be found in lakes or rivers in the form of a standing wave or tidal bore. However, surfers can also utilize artificial waves such as those from boat wakes and the waves created in artificial wave pools.

The term surfing refers to the act of riding a wave, regardless of whether the wave is ridden with a board or without a board, and regardless of the stance used. The native peoples of the Pacific, for instance, surfed waves on alaia, paipo, and other such craft, and did so on their belly and knees. The modern-day definition of surfing, however, most often refers to a surfer riding a wave standing up on a surfboard; this is also referred to as stand-up surfing.

Another prominent form of surfing is body boarding, when a surfer rides a wave on a bodyboard, either lying on their belly, drop knee, or sometimes even standing up on a body board. Other types of surfing include knee boarding, surf matting (riding inflatable mats), and using foils. Body surfing, where the wave is surfed without a board, using the surfer's own body to catch and ride the wave, is very common and is considered by some to be the purest form of surfing.

Three major subdivisions within stand-up surfing are stand-up paddling, long boarding and short boarding with several major differences including the board design and length, the riding style, and the kind of wave that is ridden.

In tow-in surfing (most often, but not exclusively, associated with big wave surfing), a motorized water vehicle, such as a personal watercraft, tows the surfer into the wave front, helping the surfer match a large wave's speed, which is generally a higher speed than a self-propelled surfer can produce. Surfing-related sports such as paddle boarding and sea kayaking do not require waves, and other derivative sports such as kite surfing and windsurfing rely primarily on wind for power, yet all of these platforms may also be used to ride waves. Recently with the use of V-drive boats, Wakesurfing, in which one surfs on the wake of a boat, has emerged. The Guinness Book of World Records recognized a 23.8 m (78 ft) wave ride by Garrett McNamara at Nazaré, Portugal as the largest wave ever surfed.

Undertow (water waves)

In physical oceanography, undertow is the under-current that is moving offshore when waves are approaching the shore. Undertow is a natural and universal feature for almost any large body of water: it is a return flow compensating for the onshore-directed average transport of water by the waves in the zone above the wave troughs. The undertow's flow velocities are generally strongest in the surf zone, where the water is shallow and the waves are high due to shoaling.In popular usage, the word "undertow" is often misapplied to rip currents. An undertow occurs everywhere underneath shore-approaching waves, whereas rip currents are localized narrow offshore currents occurring at certain locations along the coast. Unlike undertow, rip currents are strong at the surface.

Waves and shallow water

When waves travel into areas of shallow water, they begin to be affected by the ocean bottom. The free orbital motion of the water is disrupted, and water particles in orbital motion no longer return to their original position. As the water becomes shallower, the swell becomes higher and steeper, ultimately assuming the familiar sharp-crested wave shape. After the wave breaks, it becomes a wave of translation and erosion of the ocean bottom intensifies.

Landforms
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