North Carolina Sea Grant studies rip current patterns
By Rebecca Nagy, North Carolina Sea Grant
Float or swim?
Recently, this question has been at the center of a debate about what people should be told to do if caught in a rip current.
Some research, including data from the West Coast, suggests that if you are caught in a rip current and simply stay calm and float, you eventually will be brought back to shore.
But how often does this actually happen in North Carolina? And what about the beachgoers caught in rip currents that do not circulate back to land?
Spencer Rogers, North Carolina Sea Grant coastal construction and erosion specialist, is answering these questions. Along with University of North Carolina Wilmington graduate student Cobi Christiansen and a variety of partners, Rogers deployed data-logging drifters on beaches in New Hanover County and along the Outer Banks in summer 2014. The drifters recorded the velocity and frequency of rip currents, including those that ejected drifters far from shore and those that circulated back to shore. br>
“Beaches are pretty safe places for recreation but the primary exception on most ocean beaches is rip currents,” Rogers says.
“On most days, they have a relatively low velocity. But on certain days and certain shoreline conditions, they get to very dangerous velocities, faster than an Olympic swimmer can swim,” he continues.
Rogers and Christiansen built the 22 drifters from readily available plumbing materials, foam, five-pound barbells and a GPS unit that measured a drifter’s position every second. They were deployed with local and international partners on varied beaches in North Carolina.
Previous research on California beaches showed about 10 percent of the drifters were ejected into deeper waters. But most circulated back to shore.
In some circulation cells in North Carolina, swimmers caught in rip currents could keep calm and float — and eventually be brought back toward shore, by the water flow.
The circulation may continue for several circular laps — but more often than not, it ended with an offshore ejection, Rogers notes. Details on data of ejection rates are being be calculated and analyzed by Christiansen for his thesis. br>
The North Carolina data present a big question: “What threshold of ejections can you tolerate? If you’re only losing 10 percent of the people, is that an acceptable reason to say float? It’s not,” Rogers says.
“If there is any real likelihood of an ejection, you pretty much have to tell people to try and get out of it,” he explains. He cites the long-told advice to stay calm but also to begin to swim parallel to the shore until out of the rip current, which is normally fairly narrow in width.
Rogers and partners will continue their research this summer, including near Rogers’ office in Wilmington, along with drifters stationed along North Carolina’s northern beaches. Other drifters will be loaned to colleagues in South Carolina and Rogers expects more requests.
To learn more about rip currents, view video of a drifter deployment, and see a full list of partners for the North Carolina research, visit: ncseagrant.ncsu.edu/ripcurrents.