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Warning signs mark a dangerous shore break and rip current along the north shore of Oahu, Hawaii. (PHOTO: JOSHUA RAINEY PHOTOGRAPHY/SHUTTERSTOCK)

Warning signs mark a dangerous shore break and rip current along the north shore of Oahu, Hawaii. (PHOTO: JOSHUA RAINEY PHOTOGRAPHY/SHUTTERSTOCK)

Deadlier Than a Hurricane

• February 08, 2013 • 4:00 AM

Warning signs mark a dangerous shore break and rip current along the north shore of Oahu, Hawaii. (PHOTO: JOSHUA RAINEY PHOTOGRAPHY/SHUTTERSTOCK)

How the science of rip current prediction could save lives

On a late summer afternoon off the North Carolina coast, a young graduate student in civil engineering waded into a scary first-person experiment. Tuba Ozkan-Haller was the daughter of an admiral in the Turkish navy, but despite that oceanic upbringing, “I was always very tentative and extremely afraid of the water,” she says. “My poor dad was always frustrated.” As she grew up she found that the more she learned about the ocean, the less afraid she was.

“I felt like I had more control.”

On this partly cloudy afternoon she stepped into the surf—the waves weren’t very big—and side-stepped towards a rip current she had spotted from the shore. The current pulled her feet out from underneath her. This was show time. She knew to stay afloat and just enjoy the ride—she was doing this on purpose, after all—but she couldn’t help but get a bit disoriented, a bit terrified.

A few minutes later, and more than two hundred yards from the shore, the rip current let her go.

In an average year, rip currents just like the one in Ozkan-Haller’s experiment kill more Americans—from first-time ocean goers to experienced swimmers—than do hurricanes. Caught off guard, people are swept out to sea, where they tire themselves out swimming against the pull of the current, which can flow nearly as fast as Michael Phelps swims the 100-meter butterfly.

 

While shark attacks and tsunamis make headlines, rips account for 80 percent of all rescues performed by lifeguards in the United States. The combination of fear, panic, and exhaustion kills more than 100 people each year. Surfers, lifeguards, and experienced ocean-goers can usually spot a rip current relatively easily—they look for sandy, discolored water extending seaward, or a choppy stretch of ocean, generally about 10 yards wide, where the waves are lower than on either side.

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(Photos courtesy University of Delaware Sea Grant College Program)

They can avoid the current, use it as an expressway to better waves, or swim away from it by paralleling the coast.

But those instincts can be lacking for many splashing around in the surf, and if swimmers knew where the currents were located, they could better avoid the danger in the first place.

Enter Tuba Ozkan-Haller, now an associate professor at Oregon State University, who for the last five years has been working to develop a model to identify the location of rip currents up to a day in advance.

She does this by surveying the topography of the ocean floor to figure out how waves will travel over it; this then allows her to see how that mass of water can escape back from shore via a rip current. Ozkan-Haller takes all these factors and plugs them into a mathematical model she developed that predicts where and when rip currents will occur and how strong they will be.

Helping her efforts are cutting-edge surveying technologies that allow her to observe properties at the water’s surface and infer the underlying bathymetry from those observations. This is a much more efficient and accurate way to get a sense of the sea floor than the standard procedure of surveying from a boat.

“I’m totally floored by how well we can do compared to traditional surveying methods,” says Ozkan-Haller. “You can set up a radar system near a beach and get continuous estimates of the bathymetry as it evolves from day to day without ever stepping foot into the water.”

Trying to forecast rip currents is nothing new, and Ozkan-Haller is part of a lively research community studying, and perhaps forecasting, rips in the U.S. and around the world. Twenty years ago, Jim Lushine of the National Weather Service found that he could reliably predict rip current intensity by comparing lifeguard rescues to weather conditions and seeing which ones influenced rescues.

“Many National Weather Service offices presently give rip current ‘outlooks,’” says Chris Brewster, president of the United States Lifesaving Association. This is a “term they use for predictions that are not full predictions.”

Ozkan-Haller points out that the NWS forecasts the probability of occurrence, while she is running a predictive model, the way a weatherman predicts a storm.

“The kind of monitoring and prediction system that I’m dreaming up does not exist anywhere in the U.S.,” says Ozkan-Haller.

Although lifeguards are highly trained at spotting rip currents in the water, an accurate, daily prediction could be a big help. A lifeguard agency could increase staffing on days when rips were predicted, says Brewster. But, he says, in the same way fire departments may staff up during periods of high fire danger, it’s not something done on a regular basis, because each day they need to be ready for anything.

“I don’t know that every single beach along our coast needs this system,” Ozkan-Haller says, “but it feels like there’s a handful to start with that would benefit from this kind of technology.” She sees a scenario where lifeguards could record data and report to her on how accurate her predictive modeling was working.

Other applications of Ozkan-Haller’s predictive system range from the monitoring of pollutants flowing out to sea after a storm, to the transport of animal larvae that’s been spawned in the shallow waters and needs to be carried back off shore.

Still, the most exciting application is saving lives and helping people, like her, to be just a little bit less afraid of the ocean.

Matt Skenazy
Matt Skenazy, an assistant editor at Outside magazine, is a former Pacific Standard fellow. His articles have appeared in Sierra, Men’s Journal, the Surfer’s Journal, and Climbing, among others publications.

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