Coastal
Currents
Produced by the University of Delaware Sea Grant College Program & the Center for Applied Coastal Research
Rip Currents
How to Spot a Rip Current
by Wendy Carey, Jim Kirby, and Ib Svendsen1
Rip Currents
Rip currents are coastal hazards that pose serious threats
to life and safety. According to the U.S. Lifesaving Association, 80% of all surf rescues in the United States are
related to rip currents. They can occur along any beach
with breaking waves and may become especially hazardous
during high-surf conditions. Rip currents are dangerous to
all swimmers — these powerful currents may develop along
the coast at a low spot in an offshore sandbar or adjacent
to a coastal structure, where water can be funneled out to
sea in a narrow channel.
Rip Current Formation and Characteristics
Rip currents are powerful, channelized currents of swiftly
flowing water moving out to sea. They typically extend from
near the shoreline, through the surf, and out past the line of
breaking waves.
As waves break near the shore, complex wave interactions may generate circulation patterns that result in the
formation of rip currents, sending water back out to sea.
Along open coasts, rip currents are caused by variations in
breaking waves, with waves breaking strongly in some locations and less strongly in others. These variations generate
circulation cells causing water to be directed offshore. Along
shorelines where sand is deposited in an offshore bar, the rip
current often flows
through a low spot or
A BOUT T HIS S ERIES
channel cut through the
sandbar. In coastal
Coastal Currents is designed
to share timely information about
areas with structures
coastal hazards and the natural
such as groins or jetprocesses that occur along Delaties, rip currents may
ware’s shoreline. The series is
result when currents
produced by the University of Delarunning parallel to the
ware Sea Grant College Program
shore are deflected off(www.ocean.udel.edu) in partnership
with UD’s Center for Applied Coastal
shore by the structure.
Research (www.coastal.udel.edu).
The inherent variFor more information, contact
ability in rip currents
Wendy Carey, Sea Grant Marine
makes them especially
Advisory Service, at
dangerous to unwary
(302) 645-4258 or
or uninformed [email protected].
goers. For example,
a rip current can be
very narrow, or it can
extend in widths of up
A rip current can form at a break in a sandbar, where
water is funneled out to sea in a narrow channel. This
powerful current also can form along coastal structures
such as jetties, groins, and piers.
A rip current can sweep even the strongest swimmer out
to sea. Minimize your chance of being caught in a rip
current by recognizing these signs:
N A channel of sandy-colored water flowing out to sea.
N A line of foam, seaweed, or debris floating out to sea.
N A section of churning, choppy water.
N A break in the surf as the waves roll toward shore.
to 50 yards wide or more. The seaward pull of a rip current can end just beyond the line of breaking waves, or it
can continue to flow hundreds of yards out to sea.
While the average speed of a rip current can range
from 1 to 2 feet per second, some of the most powerful rip
currents have been measured at speeds of up to 8 feet per
second. This is faster than an Olympic swimmer can
swim. Changes in the size of the waves also can cause
pulses in the strength of a rip current, which can be dangerous to all swimmers and anyone entering the surf.
Rip currents do not pull people under water — they
pull people away from shore. Drowning deaths usually
occur when people are unable to keep themselves afloat
and swim back to shore. This may be due to fear, panic,
exhaustion, a lack of swimming skills, or any combination
of these factors.
If you get caught in a rip current — remain calm, and
try to float or tread water. Don’t swim against the current,
as this is difficult for even experienced swimmers. Swim
along the shoreline until you feel the current relax, or let
the current carry you until it slows down. Then swim
toward the shore at an angle. Since rip currents are narrow,
it does not take much effort to swim along the shore out
of danger’s way. If you are unable to reach shore, wave
your arms and yell for help.
Improving Public Safety
Coastal geologists and engineers have been working to
increase our understanding of this coastal hazard since the
early 1900s. A variety of techniques are used to study rip
currents including direct observations, field experiments
using instruments in the surf zone, laboratory experiments
with wave tanks, and mathematical and computer modeling.
For the past 25 years, coastal engineers at the University
of Delaware’s Center for Applied Coastal Research (CACR)
have conducted research related to the development and behavior of rip currents and how they function as a mechanism
for offshore sediment transport. The center’s research focuses
on nearshore circulation patterns as well as the forces that
drive rip current formation such as wave-wave interaction,
wave-bottom interaction, and wave-structure interaction.
Sea Grant researchers at CACR use computer models
and conduct wave-basin experiments to learn more about
the development of rip currents. Their 4,500-square-foot
wave basin is equipped with an artificial offshore sandbar
and a sloping beach. As wave and bottom conditions in the
wave 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 Nearshore
Community Model. NearCoM predicts waves, currents,
sediment transport, and other ocean conditions in the
nearshore area (extending from the shoreline to a depth of
approximately 30 feet). The model consists of a “suite of
modules” including SHORECIRC and FUNWAVE, all
developed by CACR scientists, that simulate individual
physical processes such as ocean circulation and waves.
UD’s Sea Grant College Program also cooperates with
the National Weather Service and local beach patrols to
improve rip current predictions. The Delaware Atlantic
Rip Current Project, a coordinated program between these
groups, collects information on rip current rescues as well
as physical parameters such as wind speed and direction,
wave/swell height and period, and tidal stage. This information can help determine those days that weather conditions may favor the formation of strong rip currents.
CACR coastal engineers and colleagues also are working
to develop and install coastal observation and videomonitoring systems along the Delaware and Maryland
beaches to further enhance rip current predictive models.
The work being done by Sea Grant and other research
institutes will contribute to the understanding of rip currents 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 the
beach, speak with the on-duty lifeguards about rip currents
as well as other water conditions expected for the day. And
never underestimate the power of the ocean.
Before leaving for the beach, check the forecast on
NOAA Weather Radio or on the Web. These services are
provided to the public by the National Oceanic and
Atmospheric Administration (NOAA).
Information about surf conditions at the Delaware and
New Jersey coasts can be found at www.erh.noaa.gov/er/
phi/ripcurrent/getSRF.php. Marine forecasts and tidal information for the Delmarva, New Jersey, and New York
coasts can be found at www.erh.noaa.gov/er/phi/marine.html.
More information on rip currents can be found on the
following Web sites:
N www.ripcurrents.noaa.gov
N www.usla.org
N www.ocean.udel.edu/ripcurrents
1
Dr. Ib Svendsen passed away unexpectedly in December 2004.
Before his untimely death, he contributed to the production of
this rip current fact sheet. The University of Delaware mourns
the loss of a dedicated colleague and friend.
The University of Delaware Sea Grant College Program is a member of a national network of universities
committed 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 Atmospheric
Administration 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: [email protected]. For other Sea Grant publications, visit our on-line
catalog at www.ocean.udel.edu/seagrant.
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