Rip Currents - A Public Awareness Negligence

TitleRip Currents - A Public Awareness Negligence
Publication TypeConference Paper
Year of Publication2007
AuthorsBech, E
Conference NameWorld Conference on Drowning Prevention
Date Published09/2007
PublisherInternational Life Saving Federation
Conference LocationPorto, Portugal
Other Numbers01-05
Abstract

1. Abstract

The presentation covers topics spanning from rip currents fundamentals, to numerical modelling of rip currents, mapping and classification and general information flow to the public in a number of cases.

Rip currents are considered to be a major safety problem at beaches worldwide, accounting for the majority of drowning accidents at coastal beaches.

To act safely if caught in a rip current is somewhat comparable to act safely in the traffic, e.g. when crossing a road. Crossing a road is a highly dangerous business, passing only inches from fast moving vehicles, which would either seriously wound or kill individuals or animals, not possessing a sufficient level of knowledge of the mechanisms behind the traffic patterns.

However, if you do posses the necessary knowledge and know the basic mechanisms and rules of the game in everyday traffic, you are able to be exposed to fast moving traffic and its dangers for hours every day, and still be fairly safe.

The analogy to rip currents is that if already known information about rip currents was circulated to the general public to a higher degree than it is today, many drowning and near-drowning accidents could be avoided.

Public awareness of rip currents is thus critical to reduce drowning deaths on a global scale, as well as continuous mapping and classification of rip currents on coastal beaches.

Learning Outcomes
  1. Public awareness and general information about rip currents (information)
  2. Challenges in secure identification of rip currents by laypersons and specialists (observation)
  3. Safe behaviour in the aquatic environment at the coastal beaches by the public (prevention)
Digital Media
Full Text

­2. Introduction

Denmark has approximately 7.500 km of coastline; hereof approximately 5.000 km sand beaches. The climate of Denmark is temperate, with icy water temperatures during winter, and summer time water temperatures of 17-22 degrees Celsius. Thus, swimming, surfing and bathing at the beaches is a popular recreation activity during the summer period. Along the western coast line, the economy in the coastal areas is driven by inland tourism, as well as many visitors from abroad, notably from Germany and Norway.

Surf lifesaving Denmark is the present de-facto organization for surf lifesaving activities and -research in Denmark, and is a joint venture set up in 1998 between the Danish Swimming Federation and the Tryg Foundation. The Danish Swimming Federation holds the ILS membership for Denmark, and was one of the founders of the Federation International de Sauvétage (FIS), the organization that merged with World Life Saving (WLS) to form the International Life Saving Federation (ILS) in 1993.

Photo 1: Image of Denmark

3. Background

Denmark is a very neat organized compact little society, with a long tradition of a strong central government administration, backed with good economic resources (40-60 % income tax, 25 % VAT, and additional special taxes on goods). Offshore sea rescue is since long well organized with a solid legal foundation.

Inshore rescue is the complete opposite. Only vague legislation exists, and there is no authority appointed to handle beach safety and beach management.

Drowning rates are not known with certainty, but is believed to be in line with the World Health Organization estimate for drowning accidents World Health Organization, Drowning fact sheet, WHO Injuries & Violence Prevention (2000) 2-3, implying that the drowning rate in Denmark is approximately 3-4 per 100 000 people. Of these, it is presumed that 20-30 per cent occurs in the sea, many of these are suspected to be the result of rip currents. An unknown number of non-fatal accidents are also related to rip currents. For every child drowned in the Netherlands, an additional 140 children are hospitalised for near-drowningMortality Statistics, Statistics Netherlands 1998-2001: Dutch Information System on Hospital Care and Nursing, Prismant (1998-2001); Dutch Injury Surveillance System 1998-2001, Consumer Safety Institute..

Photo 2: Image of a strong rip current in Florida after Hurricane Jeanne. Image by National Weather Service.

The fundamentals of rip currents are on a descriptive level quite simple. Rip currents can in general only be formed at sandy beaches with sandbars and incoming waves or swells. When water from the trough between the beach line and the sandbars starts running out, a rip current is formed. Rip currents come in a wide spectrum of magnitudes, ranging from very low energy micro rip currents to high energy mega rip currents. Tidal effects can also cause rip currents, estuaries and secluded coves may have permanent rip currents. Most rip currents are known not to be permanent, but pulsating with a period where the rip is active and flushes water out, and a calm period where the water is not flushing outMacMahan, J.H., Thornton, E.B., Rip current review, Coastal Engineering 53 (2006) 191 â€" 208.

The teaching of swimming in Denmark is not consistent, as the legal background for the public school system only requires mandatory “knowledge” to swimming techniques, meaning that lessons can be reduced to dry swimming, with only a few practical lessons in the pool. A recent study shows that 30 per cent of the Danish adult population cannot swim at least 200 mDanish Swimming Federation, National swimming ability survey (2007).

The conclusion to all this, is from our view that many of the annual drowning accidents are preventable through education of, and information to the public. Lifeguard services on the beaches are not a cure to the basic drowning problem, and are to be regarded as an additional service to highly populated specific beaches in the peak season.

4. Methods

To get a grip of the distribution of rip currents in Denmark, it became clear that a thorough mapping was needed. In the Danish language, there is a distinction in the phenomenology and the anatomy of rip currents. The depression or channel in the sand bars is named “hestehul” and the current it self is named “udstroem”. It was clear that mapping the active currents in a short period of time, would be a very difficult task, while mapping the depressions in the sandbars was an easier task.

Aerial mapping from 500 to 1.200 feet, at oblique angles to the beach line, was found to provide very good and comprehensive data in a cost-effective manner. In the subsequent digital image analysis, it was found that depressions in the sandbars and even rip currents became more detectable using the infra red channel.

Photo 3: Oblique image of Vejers Beach, Denmark, in the infrared spectrum, showing two rip current channels.

Various reconnaissance aircraft from the Royal Danish Air Force using cooled infra red optics, was found to be difficult to utilize due to commercial competitive legislation, so satellite images in the infra red spectrum was used as an alternative. Unfortunately, satellite infra red images available for civil purposes either have a resolution not sufficient enough for a good analysis, or the spectrum in the infra red sensors is to wide.

Subsequent ground mapping of the coast line was of course necessary to validate the findings from aerial observations. However, ground mapping is very laborious and time consuming, and furthermore it was found that observation of rip currents from the shore line without elevation, was indeed very difficult. Observation of rip currents on a beach was however found possible in specific conditions, with calm winds, moderate swells, and only very close to shore (0-50 m). Dye markers has been used, but with mixed results. The use of a dye marker may be a very efficient way to visualize a rip current, but we found that the usage requires expert knowledgeBrander, R.W., Field observations on the morphodynamic evolution of a low-energy rip current system, Marine Geology 157 (1999) 199â€"217.

Special low-tech and sturdy current buoys recently developed specifically for rip currentshttp://www.alfakinetic.dk are presently under testing, and may be a good tool at life guarded beaches to visualize currents.

The storage tool chosen for mapping a survey is very important. Our survey is still in progress, using both paper and digital maps and tables for storage of the survey. Procurement of the Australian developed ABSAMP database structure is under consideration, as this seems to fulfill all our requirements. Classification of the beaches is done primarily using the beach classification system described by Short et al.Short, A.D., Hogan, C.L., 1994. Rip currents and beach hazards: their impact on public safety and implications for coastal management. J. Coastal Res. 12, 197â€"209., combined with additional data tables such as Beach Peak Population (BPP), and other relevant local information.

In addition, recent field observations in the U.S.Powel, H., et al., NewScientist (30 June 2007) 42â€"43 shows that numerical modelling of a rip current is far more complex than assumed, implying a need to review the survey techniques and numerical modelling in actual rip currents.

It seems inherently apparent, that information to the public is the only rational way forward to reduce drowning accidents in open water.

Signage on the access ways to the beaches are being developed by Surf Lifesaving Denmark, with close cooperation of the lifesaving organizations in Great Britain and Australia. A specific sign for rip currents has been developed with inspiration from Hawaii, mainly to be used at the beaches at the west coast of Jutland.

Photo 4: Signage for warning of rip currents in Denmark 2007.

New bathing rules was developed in 2005 to cut the many good â€" but multiple â€" former advices. The new “five-finger rules” are:

  • Learn to swim
  • Never swim alone
  • Check out the wind direction, the currents and the water depth before bathing
  • Check out specific local conditions before bathing
  • Children are always to be under constant adult supervision when bathing

These five simple rules have proved to be efficient â€" when known to the bather â€" to increase the safety awareness at the beach.

5. Results

Aerial surveillance provides â€" under optimal conditions â€" clear indications of rip currents from air

Ground mapping outcome was poor in a cost-effective context, but however necessary to validate data. Ground mapping is also mandatory to obtain a reliable and trustworthy risk assessment of a beach. It has been proved that depressions in the sandbars â€" with the possibility of adjacent rip currents â€" are a natural phenomenon along the Danish coastline, occurring with a 50-400 m spacing. The phenomenon is so common along the west coast of Jutland that most regular bathers here must have been in a rip current sooner or later. Many of them perhaps didn't notice it, giving the current was not active at the moment or strong enough to pose a problem.

6. Discussion and conclusions

Should the lifesaving organizations be solely active to prevent drowning accidents in open water?

Giving that many drowning accidents are related to rip currents, a massive effort must be undertaken to educate the general public, to put up signage and to constantly survey relevant bathing areas. A lifesaving organization may have some of the roles in this context, but surely governmental institutions must take responsibilities in preserving lives in the general public health paradigm. As well as road traffic safety is regulated in a society with legislation and safety standards, legislation and safety standards for recreational bathing on public and private beaches and in pools seems obviously to be a government issue.

Drowning is in most countries the second primary cause of accidental death next to traffic accidents, in some age groups drowning is the primary accidental cause of death [1].

7. Take Home Messages

  • Swimming lessons will save lives.
  • Knowing the simple mechanics of a rip current will save lives.
  • Public signage with warning against rip currents, littoral currents or backwash will save lives.
  • Educate the public and the authorities of the risks of drowning at beaches were rip currents can occur.
  • Positive identification of a rip current â€" both for laypersons and specialists â€" can be very difficult on the beach. Use an elevated platform e.g. a structure, dunes or aircraft for observation.