New research improves predictions of dangerous rip currents

SHARE THIS: 

New research about how the configuration of beaches and climate cycles affect rip currents will help improve the accuracy of forecasts of when and where dangerous rips occur on New Zealand beaches, potentially saving lives.

Contents

The research builds on a 10-year collaborative project between NIWA and the University of Waikato to study and forecast rip currents at Tairua Beach in the Coromandel.

Using images from a computer-controlled camera set up at the end of the beach, scientists have been looking at how rips develop, migrate and change over a 10-year period to build models to forecast rip occurrence.

A rip is an offshore current concentrated in a narrow channel along a beach, often catching swimmers unaware and pulling them out to sea.

Generally, the orientation, size and strength of rip currents depend on offshore wave conditions, including height and angle of the waves. By analysing wave characteristics against rip currents on the video images over a 5-year period, a predictive model to forecast rip occurrence was developed. Seventy-five percent of the time the model accurately predicted a rip current would occur.

Now new research is looking at how the shape and configuration of the beach – including the location of sandbars, channels, and the position and slope of the shoreline – can impact rip currents, to improve the accuracy of the forecasts.

University of Waikato senior lecturer Dr Karin Bryan says the new analysis provides exciting information about how stable rip currents are, where they might develop and how many there might be.

“Looking at the video you can clearly see some rip currents that did not move for nearly a year, especially near the headlands. At the central part of the beach, you might see up to 8 or 9 currents occurring. The central ones are really different, shifting and changing and even disappearing after a few weeks. We can extract precise measurements of these rips, which are used to fine-tune our model for forecasting rip currents, ultimately providing the level of accuracy needed to help surf lifesaving initiatives.”

Scientists have also been looking at how La Niña and El Niño climate cycles impact rip currents.

“With each climate cycle the beach rotates, pushing all the sand to one end of the beach. That movement is really controlling the size, stability and location of rip currents,” Dr Bryan says. “It’s the first time we have really analysed how these large-scale patterns control the smaller scale rip current patterns.”

NIWA coastal scientist Dr Giovanni Coco says the biggest gap in global knowledge on rips is how currents react with the seabed.

“As a rule we know the larger the waves, the stronger the rip. But that’s not the only factor. We are now getting a much clearer idea of how beach morphology, shape and structure are related to rips developing. Because we have been collecting video data for so long at Tairua, we are in a unique position to be able to do this kind of work.”

“It’s a significant step forward internationally,” Dr Coco says.

Surf Lifesaving New Zealand Life Saving Services and Education Manager, Brett Sullivan, says a high proportion of drownings that occur on the coast are directly related to rips. They are also responsible for the majority of rescues performed by lifeguards.

“Rips are a significant hazard on New Zealand beaches and Lifeguards spend many hours working to reduce the risk they pose to the public. People drown fast so any new research that helps Lifeguards to focus their attention and lifesaving equipment to where it is needed most, certainly has the potential to save lives.”

The research is a long-term collaborative project between NIWA and the University of Waikato, assisted by Environment Waikato.

 

For comment, contact:

Dr Giovanni Coco

Coastal & Estuarine Processes

NIWA, Hamilton

Dr Karin Bryan

Senior Lecturer, Department of Earth and Ocean Sciences

University of Waikato

Background

What is Cam-Era?

NIWA's Cam-Era project NIWA runs 12 fixed video cameras at beaches around the country. These are computer-controlled for real-time coastal monitoring of currents (including rips) in relation to wave height and the position of sandbars. The data is used for research purposes. Images are updated hourly on the website for public use.

More information is available on the Cam-Era section of our website.

What to do in a rip (advice from Surf Life Saving New Zealand)

A swimmer caught in a rip should not panic. The swimmer should ride the current out from the beach until the current weakens, then swim parallel to the shore for30-40 metres before returning to shore, swimming slowly.

If in trouble:

Float on your back.

Raise your hand.

Wait until the rip stops moving before swimming.

For more information, go to the Surf Life Saving NZ website.

Rip tide at Tairua, October 2010.

Archived

This page has been marked as archived, and is here for historical reference only.

Information provided may be out of date, and you are advised to check for newer sources in this section.

This content may be removed at a later date.