Rip currents are coastal hazards that pose serious threatsto life and safety. According to the U.S. Lifesaving Asso-ciation, 80% of all surf rescues in the United States are related to rip currents. They can occur along any beachwith breaking waves and may become especially hazardousduring high-surf conditions. Rip currents are dangerous toall swimmers these powerful currents may develop alongthe coast at a low spot in an offshore sandbar or adjacentto a coastal structure, where water can be funneled out tosea in a narrow channel.

Rip Current Formation and CharacteristicsRip currents are powerful, channelized currents of swiftly

flowing water moving out to sea. They typically extend fromnear the shoreline, through the surf, and out past the line ofbreaking waves.

As waves break near the shore, complex wave inter-actions may generate circulation patterns that result in theformation of rip currents, sending water back out to sea.Along open coasts, rip currents are caused by variations inbreaking waves, with waves breaking strongly in some loca-tions and less strongly in others. These variations generatecirculation cells causing water to be directed offshore. Alongshorelines where sand is deposited in an offshore bar, the rip

current often flowsthrough a low spot orchannel cut through thesandbar. In coastalareas with structuressuch as groins or jet-ties, rip currents mayresult when currentsrunning parallel to theshore are deflected off-shore by the structure.

The inherent vari-ability in rip currentsmakes them especiallydangerous to unwaryor uninformed beach-goers. For example, a rip current can bevery narrow, or it canextend in widths of up

to 50 yards wide or more. The seaward pull of a rip cur-rent can end just beyond the line of breaking waves, or itcan continue to flow hundreds of yards out to sea.

While the average speed of a rip current can rangefrom 1 to 2 feet per second, some of the most powerful ripcurrents have been measured at speeds of up to 8 feet persecond. This is faster than an Olympic swimmer canswim. Changes in the size of the waves also can causepulses in the strength of a rip current, which can be dan-gerous to all swimmers and anyone entering the surf.

Rip currents do not pull people under water theypull people away from shore. Drowning deaths usuallyoccur when people are unable to keep themselves afloatand swim back to shore. This may be due to fear, panic,exhaustion, a lack of swimming skills, or any combinationof these factors.

If you get caught in a rip current remain calm, andtry to float or tread water. Dont swim against the current,as this is difficult for even experienced swimmers. Swimalong the shoreline until you feel the current relax, or letthe current carry you until it slows down. Then swimtoward the shore at an angle. Since rip currents are narrow,it does not take much effort to swim along the shore outof dangers way. If you are unable to reach shore, waveyour arms and yell for help.

Rip Currentsby Wendy Carey, Jim Kirby, and Ib Svendsen1

Produced by the University of Delaware Sea Grant College Program & the Center for Applied Coastal Research

ABOUT THIS SERIESCoastal Currents is designed

to share timely information aboutcoastal hazards and the naturalprocesses that occur along Dela-wares shoreline. The series is produced by the University of Dela-ware Sea Grant College Program(www.ocean.udel.edu) in partnershipwith UDs Center for Applied CoastalResearch (www.coastal.udel.edu).

For more information, contactWendy Carey, Sea Grant MarineAdvisory Service, at(302) 645-4258 orwcarey@udel.edu.

CoastalCurrents

How to Spot a Rip Current

Rip Currents

A rip current can form at a break in a sandbar, wherewater is funneled out to sea in a narrow channel. Thispowerful current also can form along coastal structuressuch as jetties, groins, and piers.A rip current can sweep even the strongest swimmer outto sea. Minimize your chance of being caught in a ripcurrent by recognizing these signs: A channel of sandy-colored water owing out to sea. A line of foam, seaweed, or debris oating out to sea. A section of churning, choppy water. A break in the surf as the waves roll toward shore.

Improving Public SafetyCoastal geologists and engineers have been working to

increase our understanding of this coastal hazard since theearly 1900s. A variety of techniques are used to study ripcurrents including direct observations, field experimentsusing instruments in the surf zone, laboratory experimentswith wave tanks, and mathematical and computer modeling.

For the past 25 years, coastal engineers at the Universityof Delawares Center for Applied Coastal Research (CACR)have conducted research related to the development and be-havior of rip currents and how they function as a mechanismfor offshore sediment transport. The centers research focuseson nearshore circulation patterns as well as the forces thatdrive rip current formation such as wave-wave interaction,wave-bottom interaction, and wave-structure interaction.

Sea Grant researchers at CACR use computer modelsand conduct wave-basin experiments to learn more about the development of rip currents. Their 4,500-square-footwave basin is equipped with an artificial offshore sandbarand a sloping beach. As wave and bottom conditions in thewave basin are varied, data are collected on subsequent

changes in rip current conditions. These measurements,along with field data, are used to help test the NearshoreCommunity Model. NearCoM predicts waves, currents,sediment transport, and other ocean conditions in thenearshore area (extending from the shoreline to a depth ofapproximately 30 feet). The model consists of a suite ofmodules including SHORECIRC and FUNWAVE, alldeveloped by CACR scientists, that simulate individualphysical processes such as ocean circulation and waves.

UDs Sea Grant College Program also cooperates withthe National Weather Service and local beach patrols toimprove rip current predictions. The Delaware AtlanticRip Current Project, a coordinated program between thesegroups, collects information on rip current rescues as wellas physical parameters such as wind speed and direction,wave/swell height and period, and tidal stage. This infor-mation can help determine those days that weather con-ditions may favor the formation of strong rip currents.CACR coastal engineers and colleagues also are workingto develop and install coastal observation and video-monitoring systems along the Delaware and Marylandbeaches to further enhance rip current predictive models.

The work being done by Sea Grant and other researchinstitutes will contribute to the understanding of rip cur-rents and increase public awareness of their danger. The Latest Information on Rip Currents

How can you protect yourself against rip currents?Learn how to swim, and never swim alone. If possible,swim at beaches with lifeguards. When you arrive at thebeach, speak with the on-duty lifeguards about rip currentsas well as other water conditions expected for the day. Andnever underestimate the power of the ocean.

Before leaving for the beach, check the forecast onNOAA Weather Radio or on the Web. These services areprovided to the public by the National Oceanic andAtmospheric Administration (NOAA).

Information about surf conditions at the Delaware andNew Jersey coasts can be found at www.erh.noaa.gov/er/phi/ripcurrent/getSRF.php. Marine forecasts and tidal in-formation for the Delmarva, New Jersey, and New Yorkcoasts can be found at www.erh.noaa.gov/er/phi/marine.html.

More information on rip currents can be found on thefollowing Web sites:

www.ripcurrents.noaa.gov www.usla.org www.ocean.udel.edu/ripcurrents

1 Dr. Ib Svendsen passed away unexpectedly in December 2004.Before his untimely death, he contributed to the production ofthis rip current fact sheet. The University of Delaware mournsthe loss of a dedicated colleague and friend.

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The University of Delaware Sea Grant College Program is a member of a national network of universitiescommitted to research, education, and technology transfer designed to meet the changing needs of U.S. ocean,coastal, and Great Lakes regions. The program is financially supported by the National Oceanic and AtmosphericAdministration in the U.S. Department of Commerce; the State of Delaware; and the University of Delaware. For more information, please contact the UD Marine Public Education Office, Newark, DE 19716-3530. Phone: (302) 831-8083. E-mail: MarineCom@udel.edu. For other Sea Grant publications, visit our on-line catalog at www.ocean.udel.edu/seagrant.

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