Rip Currents University of Delaware Sea Grant College Program

 

University of Delaware NOAA Sea Grant
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How to Identify a  Rip Current

 

Over the past 20 years, Sea Grant and other funding agencies have sponsored rip current research at many of the nation’s premier universities. Coastal scientists are working to increase our understanding of rip currents through a variety of techniques including field experiments in the surf zone, laboratory experiments in wave tanks, and mathematical and computer modeling.

Through these laboratory and field research projects, we have learned that rip currents can be found on many surf beaches every day and rip current speeds can vary. Under certain wave, tide and beach conditions rip currents can quickly become dangerous to anyone entering the surf. Average rip current speeds of 1-2 feet per second can sweep even the strongest swimmer out to sea. And rip currents have been measured as fast as 8 feet per second, which is faster than an Olympic swimmer can sprint.

It is critical that the results of these research efforts aren’t shelved with dissertations and scientific papers – Sea Grant synthesizes science-based information and gets it to those who need it. An example of this is the Rip Current Technical Workshop that NOAA’s Sea Grant and National Weather Service convened in Florida in April 2004. The workshop improved communication between research scientists and forecasters and helped to identify data gaps, partnership opportunities and future research needs that will enhance and improve rip current prediction and forecasting.

If you would like to submit a current research project to this list click here.The work being done by Sea Grant and other research institutes will help reduce the risk that a rip current poses to public safety by contributing to our understanding of this coastal hazard and increasing awareness of its danger.

2004 NOAA Rip Current Technical Workshop

NOAA-Sea Grant and NOAA-National Weather Service convened a technical workshop on rip current research and forecasting on April 6-7 in Jacksonville, Florida. The workshop was held to enhance communication and information sharing among National Weather Service forecasters, coastal research scientists, and Sea Grant outreach personnel. Each organization presented its latest rip current research, forecasting methodologies, and hands-on data applications. The workshop also helped each agency identify data gaps, partnership opportunities and future research needs to enhance and improve rip current prediction and forecasting. A strong commitment from all agencies was made by attendance – forty-eight participants, representing sixteen states, were actively involved in workshop presentations and discussions.

Click here to view workshop overview and agenda

Rip Current Research Projects:


DELAWARE
University of Delaware – Center for Applied Coastal Research (CACR)
For the past 25 years, coastal engineers at the University of Delaware’s Center for Applied Coastal Research (CACR) have conducted numerous research projects related to the development and behavior of rip currents and how they function as a mechanism for offshore sediment transport. Their 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 are using computer models and wave basin experiments to learn more about the development of rip currents. In the research laboratory, a 4,500-square-foot wave basin is used to study rip currents and their interaction with an artificial offshore bar and sloping beach. As wave and bottom conditions in the wave basin are varied, observations and data are collected on subsequent changes in rip current characteristics. These measurements, along with available field data, serve a significant role as a benchmark for testing the recently completed NearCoM model (for Nearshore Community Model), which incorporates a number of individual model components developed by CACR, including the Shorecirc circulation model and the Funwave shallow water wave model.

University of Delaware – Marine Advisory Service
University of Delaware’s Sea Grant Marine Advisory Service is cooperating 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, is collecting 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.

    


NEW JERSEY
Stevens Institute of Technology
Coastal engineers at the Stevens Institute of Technology are working on several research projects that will improve understanding of rip current formation and behavior along the New Jersey coast. Dr. Tom Herrington and others have installed a system of nearshore pressure gauges that provide data on water level, wave height and wave period. These data are used by coastal engineers and the National Weather Service to determine correlations between nearshore wave characteristics and rip current occurrence.

Dr. Herrington is also working towards formulation of an experimental Rip Current Index based on the relationships between waves and currents in the surf zone (both cross-shore currents and alongshore currents). Additionally, research is being conducted related to the impact of coastal structures on nearshore currents. Dr. Herrington is investigating the impacts of shore perpendicular structures (such as groins and jetties) on longshore currents and rip currents. Future work will involve the interaction between these currents, nearshore bathymetry (shape of the bottom), beach fill projects, and modified coastal structures such as notched groins.


(Photo courtesy of Dr. Tom Herrington,
Stevens Institute of Technology)



MARYLAND
Johns Hopkins University
Dr. Robert A. Dalrymple (Johns Hopkins University) has more than 30 years experience in rip current research and nearshore coastal processes, including field observations and measurements, laboratory studies and computer modeling, and theory and numerical modeling. Presently, Dr. Dalrymple has initiated a project with Sea Grant funding that will incorporate video imaging into analyses of surf zone dynamics and occurrence of rip currents.

The project will involve coordination with members of the Ocean City (Maryland) beach patrol, who will assist by providing rip current rescue data. The video imaging technology will permit coastal engineers to make field observations of the conditions under which rip currents are generated. These data and observations will then be incorporated into a data base that will enhance and improve rip current prediction and forecasts.
(Photograph courtesy of Delaware Sea Grant)

NORTH CAROLINA
U.S. Army Corps of Engineers Coastal Hydraulics Laboratory and Field Research Facility, Duck, North Carolina
For more than 25 years, the U. S. Army Corps of Engineers Field Research Facility located at Duck, North Carolina, has served as an experimental station and field site for coastal research. Investigations have been conducted on waves, winds, tides, currents, and sediment transport using a variety of equipment and technologies. Additional information and details about the Field Research Facility can be found on their Web site: http://www.frf.usace.army.mil/.

Rip current-related field work has been conducted at the Duck facility by coastal scientists from many different government and academic institutions. An example of a recent rip current field study involved coastal engineers from the University of Florida, Gainesville. Dr. Robert G. Dean and graduate student Jamie MacMahan, used current meters in the surf zone to document the occurrence and behavior of rip currents over a six month period. The study included analysis of 2.5 years of hourly time-lapse photography of shoreline areas prone to rip current occurrence along a section of the North Carolina coast. The results of the study included information demonstrating that rip currents may persist for weeks or months at the same location along a coast, and that certain parts of a shoreline may be more prone to rip current development than others. Additionally, current meter data showed that rip current velocities may become dangerously strong under specific conditions.

University of North Carolina, Wilmington
Coastal scientists at the University of North Carolina, Wilmington, are coordinating to install a nearshore wave gauge that will provide information on wave height, period, and direction. These data will be used to verify and enhance surf zone forecasts and rip current outlooks along the North Carolina coast. Spencer Rogers, North Carolina Sea Grant Program, is coordinating with the National Weather Service office in Wilmington, North Carolina, to coordinate and facilitate data sharing opportunities.


GEORGIA
Georgia Tech, Savannah
Dr. Kevin Haas, Georgia Tech, Savannah, has been involved in rip current research for more than a decade. As a graduate student and post-doctoral research scientist at the University of Delaware’s Center for Applied Coastal Research, Dr. Haas worked with Dr. Ib Svendsen and others to develop and test the SHORECIRC nearshore circulation model. Using laboratory data obtained in wave tank experiments, the SHORECIRC model was able to verify the formation of rip currents. While at the University of Delaware’s Center for Applied Coastal Research, Dr. Haas conducted experiments to measure hydraulic gradients in rip current systems.

At the present time, Dr. Haas is continuing his research related to numerical and physical modeling of rip current systems. An active research project involves video tracking of rip current movement in a laboratory wave tank.

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FLORIDA
University of Florida, Gainesville

Coastal engineers at University of Florida’s Department of Civil and Coastal Engineering have conducted nearshore and coastal engineering research for many years. Over the past decade, Dr. Robert G. Dean, Dr. Robert Thieke, Dr. Donald Slinn, Dr. Andrew Kennedy, other faculty members as well as graduate students have been principal investigators on many rip current and nearshore circulation research projects.

For example, Dr. Dean and graduate student Jamie MacMahan studied characteristics and behavior of rip currents at the Field Research Facility in North Carolina’s Outer Banks. Analysis of thousands of time-elapsed photos of rip currents along the North Carolina coast demonstrated that location of rip currents was persistent for weeks or months, and that rip current velocities could quickly become extremely dangerous under certain wave and surf conditions.

Dr. Thieke and graduate student Jason Engle worked with Florida beach patrols in Volusia County and the Florida Panhandle to examine the relationship between rip current rescues and wave and weather conditions. Their findings showed that the frequency of rip current rescues increased when waves approached the shore straight on (shore normal wave incidence as opposed to waves coming in at an angle), and at mid-low tidal stages. These results can be used to enhance the rip current forecasting techniques used by the National Weather Service by including parameters such as wave direction and tidal stage in the NWS predictive matrix. University of Florida is continuing to work with local weather forecast offices to enhance and verify surf zone forecasts and rip current outlooks.

Dr. Andrew Kennedy has conducted research related to generation of rip currents and nearshore circulation patterns, and he is presently working on dynamical approaches to compute the overall forcing mechanisms that drive rip current development. Rip current video tracking and nearshore circulation cell development are also a focus of research being conducted at the University of Delaware’s Center for Applied Coastal Research wave tank in coordination with Dr. Kevin Haas and graduate students. Dr. Kennedy is also working with local beach patrols in Florida to develop a program to obtain nearshore observations of wave, current, and bottom conditions that correlate to rip current occurrence.

University of South Florida
Dr. Richard A. Davis, coastal geologist at the University of South Florida, has conducted research on the impacts of coastal morphology on rip current development and circulation. Improved knowledge and detailed information on specific shoreline configuration (shape) may lead to improved prediction of the likelihood of rip current development. The presence of longshore bars and their bathymetry can influence rip current development and location. Dr. Davis has also worked to promote rip current outreach, education, and awareness on local, regional, national, and international levels.


CALIFORNIA
Naval Postgraduate School
A significant amount of rip current research has been conducted by scientists at the Nearshore Processes Laboratory, Oceanography Department at the Naval Postgraduate School in Monterey, California. Dr. Ed Thornton, graduate students, and research associates have been involved in a number of investigations related to nearshore coastal processes, surf zone circulation patterns, breaking waves, currents, and sediment transport. Using instrument arrays (current meters, wave staffs, pressure gages, other sensors) in the nearshore and surf zone, breaking wave parameters and associated current velocities (both longshore and cross-shore) have been measured. Additional information on the NCEX (Nearshore Canyon Experiment) investigations of coastal processes can be found at: http://science.whoi.edu/users/pvlab/NCEX/index.html.
(Photo courtesy of Dr. Andrew Kennedy)


The RIPEX/Steep Beach Experiment (http://www.oc.nps.navy.mil/ripex/) involved investigation of rip currents and
wave transformation at a field site located at Monterey Bay, California. The multi-faceted project consisted of experiments to measure waves, currents, sediment transport, and nearshore bathymetry.

It involved faculty, staff, and students from the
Naval Postgraduate School, Ohio State University,
and University of Florida, Gainesville.

(Photos courtesy Dr. Jamie MacMahan)

Scripps Institution of Oceanography
At Scripps Institution of Oceanography, Dr. Robert Guza and others have used drifter studies in the nearshore to study the life-cycle of rip currents. The investigation focused on eddy formation and circulation patterns in the nearshore zone using drifters outfitted with GPS (global positioning system) technology. By tracking the movement of the drifters, the scientists are able to determine the velocity, strength, and size of rip currents.


OREGON
Oregon State University
The faculty and staff at the O. H. Hinsdale Wave Research Laboratory and College of Oceanic Atmospheric Sciences at Oregon State University are actively involved in research related to coastal processes, nearshore hydrodynamics and circulation patterns, bathymetric impacts on waves/currents, sediment transport in the surf zone, wave modeling, and rip current modeling. Dr. Merrick Haller, Dr. Tuba Ozkan-Haller, Dr. Robert Holman, and others have been extensively involved in rip current research and nearshore circulation modeling projects including NCEX (Nearshore Canyon Experiment) that incorporated field observations and measurements of waves, currents and bathymetry into simulated models of waves and nearshore circulation.


(Photo of rip current at NCEX project site –
adjacent to Scripps pier; photo courtesy of Dr. Merrick Haller)


MICHIGAN
University of Michigan, Ann Arbor
Dr. Guy Meadows

Dr. Guy Meadows, Director of University of Michigan’s Ocean Engineering Laboratory, has investigated nearshore coastal processes, waves, and currents in the Great Lakes. His research interests include field and analytical studies of marine environmental hydrodynamics with emphasis on mathematical modeling of nearshore waves, currents and shoreline evolution. Additionally, Dr. Meadows is working to develop in situ and remote oceanographic instrumentation systems that will permit measurement of spatial and temporal structure of coastal boundary layer flows, including active microwave remote sensing of ocean dynamics including wave/wave, wave/current, wave/topographic interactions. Dr. Meadows participated in the 2004 Rip Current Technical Workshop, presenting an overview of rip currents in the Great Lakes. (Photo of rip channels in Lake Michigan; photo courtesy of Dr. Guy Meadows).


OHIO
Ohio State University

Dr. Thomas Lippmann, senior research scientist at the Ohio State University College of Engineering, has been involved in rip current research programs along the west coast. Dr. Lippmann has worked with Dr. Holman on the relationship between nearshore bathymetry and rip current occurrence. Using video technology, their studies included investigations of spatial and temporal variability of sand bars, and quantification of wave dissipation over the bars. Dr. Lippmann’s current research interests include nearshore fluid-sediment interactions including large-scale coastal evolution, sand bar formation by low frequency wave motions and sediment suspension, as well as remote sensing with video imaging techniques, and surfzone wave modeling by numerical models predicting wave transformation and breaking. (Photo – Example of west coast rip currents. Photo courtesy of Dr. Lippmann and Dr. Andrew Kennedy)


JAPAN

Rip currents are recognized as a serious coastal hazard in Japan. Professor Ryuichiro Nishi, Department of Ocean Civil Engineering, Kagoshima University, has been conducting rip current research and education/outreach programs in Japan. Professor Nishi has compiled a digital archive of rip current photographs that cover most of the Japanese coastline, and has worked to coordinate agencies and heighten awareness about the hazards associated with rip currents in Japan.


AUSTRALIA

A significant number of rip current field research projects involving scientists from varied academic institutions have been conducted along the Australian coast. In a major experiment sponsored by Sea Grant and NOPP at Moreton Island in Queensland, Dr. Kevin Haas and others conducted field tests and compared results to rip current computer models. Field experiments were conducted with current meter arrays (longshore currents and cross-shore currents), stilling wells (tides, water level), bathymetric surveys, and dye studies. Results of the experiments demonstrated that rip currents contain strong vertical velocity variations due to interaction with breaking waves, and that rip currents pulsate with incoming wave groups. Hydraulic gradients in a small rip current system were also measured. These data were incorporated into numerical and computer models to study rip current behavior. Computer model results computed with the Shorecirc model, showed excellent agreement with the collected data.
(Rip current experiment along the Australian coast – Photo courtesy of Dr. Kevin Haas).

At the Rip Current Technical Workshop (April, 2004), Dr. Merrick Haller reported that a study of rip morphology dynamics was conducted at a location at Palm Beach, Australia, using Argus video technology. The video imaging of the shoreline and surf zone permitted scientists to develop a time-series of rip current location, duration, and channel movement over a period of two years.

For over 20 years, Dr. Andrew Short, Coastal Studies Unit, Department of Geography, University of Sydney, has investigated rip currents in Australia. Dr. Short has published papers on rip current type, spacing, and persistence, and has also worked to develop education and awareness programs about the hazards of rip currents. Dr. Short has worked with beach safety organizations in Australia to produce outreach programs and publications that combine descriptions of shoreline type/characteristics with surf zone safety information, with special emphasis on rip currents. These awareness projects have been used as models to establish coastal hazard programs in several other countries.



Brazil

Note: The following information has been submitted by Antonio Henrique da Fontoura Klein from the University of Vale do Itajaí, Brazil.

Antonio H. F. Klein and others have been working in southern Brazil on a beach morphodynamic and hazards study that includes an analysis of beach state and rip currents. Primary objectives of their study were to systematically gather information on physical characteristics of beaches and their associated natural and human-induced hazards, along with the primary socio-economic attributes of beach users. The abstract of their recent paper entitled Beach Safety Management on the Coast of Santa Catarina, Brazil, is included below.

“This paper presents an assessment of beach safety management in the coast of Santa Catarina, southern Brazil, using results of eight years of data collected between 1995 and 2003. Four main factors play a significant role in beach accidents: (1) Landscape defines the use of coastline and the number of beach users; embayed beach are more popular; (2) Rip currents are the main natural hazard for bathers (82% of accidents); (3) The number of people on the beach contributes to beach accidents. As the number of people increases, bathers tend to move to the backshore and surf zone, causing accidents to occur; and (4) Social factors include hazard signal perception and type of beach users. The majority of accidents occur in well-signed places, where red flags on the beach and yellow flags on the lifeguards post are clearly displayed, as well as in low waves and weak rip currents conditions. The most important outcome of this project has been the implementation of a beach safety program for northern coast of Santa Catarina (100 km length), which has led do an 80% reduction in fatal accidents.”

Additional information can be found on the project Websites: http://siaiacad05.univali.br/~spraias/ and http://200.169.63.95/praia/


Iran

Note: The following information has been submitted by Behnam Shafiei Sabet, University of Guilan, MI, Iran.

Behnam Shafiei Sabet, University of Guilan (Iran), has been working on a project investigating rip current zones along Caspian Sea beaches:

The Caspian Sea has a 800-km coastline of which two-thirds consist of beautiful sandy beaches. Sporadically, surf drownings have been reported at a few stretches of the beach. From 2004 to 2006, number of drownings in Iranian Caspian Sea beach was 850. In this project we are studying surf-zone currents along the Caspian Sea beaches in Iran and investigate rip current zones along the beaches.


Argentina

The following updated information was submitted by Alberto Eugenio Mendez, from the Union Guardavidas De Mar, Argentina. (Contact information: ugm@guardavidas-mdp.org.ar)

The research project title is: Prevencion en Playas de Mar, and the project website is: www.guardavidas-mdp.org.ar

Project Description (Updated information – as submitted in Spanish)

En la ciudad de Mar del Plata, Provincia de Buenos Aires de la República Argentina Latitud: 38° 0' Sur - Longitud: 57° 33' Oeste. Las zonas de baño de las playas son casi siempre alteradas debido a la acción de las olas y las mareas y en algunos casos lamentablemente contribuye la mano del hombre.

La acción que proviene de la Naturaleza nos dice que estas alteraciones se producen principalmente por los factores que originan las olas en el mar. El viento en su dirección del mar al continente, la intensidad, el área de barrido y su duración son directamente proporcionales en cuanto a las dimensiones del oleaje. Por otro lado la orientación geográfica de la playa y el tipo de zona de baño modificada de acuerdo a su consistencia, teniendo en cuenta el avance y retroceso mareológico desde y hacia la costa, hace que las olas impacten en forma continúa aunque produciendo modificación en el flujo y reflujo de acuerdo a la amplitud de la marea. Todo ello hace que se generen imperfecciones (pozos que se continúan en canales, erosión de bancos de arena, etc.), los cuales crean las corrientes de retroceso, que yo denomino succiones de agua y no corrientes de retorno. El cambio de denominación, se debe a mi perspectiva de investigación pues tomo al bañista como sujeto de estudio en sus prácticas acuáticas con respecto a la naturaleza y no la naturaleza en su accionar.

El desencadenante y motor principal en el arrastre dentro de las succiones de agua en los bañistas, se debe a la acción de las mareas y al mecanismo regulador atribuido a las sicigias y cuadraturas en lo que amplitud se refiere y en segundo plano sin desmerecer su energía el reflujo de ola.

Que procedimientos utilicé para el entendimiento de estas fuerzas. Que seguramente en zonas de baño con características similares a las nuestras tendrían equivalente desenlace.

Teniendo en cuenta que no existe otro colega en mi país que se dedique a mi perfil de investigación y al solo contar con el importante apoyo del Cuerpo de Guardavidas que colabora realizando registros y seguimientos, sin poder utilizar recursos más elaborados que signifiquen erogación de dinero, pues solo dispongo de aporte personal, ya que el realizado por los socios que conforman nuestra institución alcanza apenas para mantenerla en sus requisitos legales.

La herramienta más importante es la observación, sea esta participante o no. Por ejemplo se puede observar que cuando existen vientos en calma (sin oleaje), pero aún perduran las canalizaciones por alteraciones a consecuencia de días anteriores; la acción de la marea proporciona igualmente fuerzas de arrastre. O establecer el día y horario indicado para concurrir a playas con succión de agua, donde se puede observar al Guardavidas realizando trabajos de prevención y rescate acuático. Otro método de investigación fue proporcionar una planilla de cuadro de doble entrada a los Guardavidas, quienes registraron los accidentes y cuyos resultados fueron cruzados con la consecuencia mareológica, resultando que más del 80% de estos accidentes se producían en bajamar y especialmente se incrementaban con las grandes amplitudes. Otro elemento utilizado fue entregar a los Guardavidas un calendario mensual con la interpretación a futuro de las acciones determinantes del proceso de energía en las succiones de agua por día y horario, el cual fue evaluado por este personal, obteniendo una conclusión más que satisfactoria.

Por lo que crear un nexo entre el Guardavidas y el ignoto Bañista es parte de la solución en la prevención acuática en las zonas de baño de nuestras playas y la educación con un dispositivo tangible, operado por Guardavidas tendrá un resultado que al decodificar la información se entablara un parámetro acrecentando el acervo cultural. Por ello hace tres años venimos prodigando este Sistema de Prevención en Playas de Mar, capacitando al profesional e informando en las Escuelas de Guardavidas; algunas de las cuales ya han incorporado este material como contenido educativo. Pero en nuestra ciudad necesitamos educar a los Gobernantes pues no sólo no comprenden la importancia de la prevención en el mar, sino que también la soslayan por otros intereses.



Denmark

The following information has been submitted by Jan Thomsen, Managing Director, alfa-Kinetic Aps, Denmark (contact: jan1@city.dk; website: www.alfakinetic.dk).

“The safety buoy “Stream indicator buoy” is this summer being tested at 10 beaches in Denmark. At some of the beaches rip current happens. A report of the results will be worked out later this summer. If you are interested in the results, please let me know. “

The test is financially supported by private and public means in cooperation with the Danish lifesaving association and the Blue Flag organization.

The buoy is developed to show the speed and direction of the current. For details about the current-sensitive buoy see the website, www.alfakinetic.dk

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RIP CURRENT RESEARCH PROJECTS

 

 

 

 

 

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