NZ's drowning numbers are amongst the worst in the world so what can we do to stay safe in the water? Video / NZ Herald
New research showing deadly rips are more complex than first thought could prompt lifeguards to re-think what safety messages they give around them.
Findings from a high-tech pilot study undertaken at popular Mt Maunganui beach, along with other fresh insights from overseas, have dispelled commonly held beliefs around the flowdirection and undercurrent of rips.
Rips - strong currents of water that run out to sea - remain one of the biggest dangers to people on the country's coasts.
About 85 per cent of the average 1200 rescues lifeguards make each year involve them.
Yet to date, there's been little research on them, and most of our historical knowledge comes from veteran lifeguards all too familiar with them.
A study led by Surf Life Saving New Zealand researcher Dan Lee, and supported by software company Emsisoft, deployed drone-mounted cameras and GPS-tracking dummies, called "drifters", at Mt Maunganui's Main Beach.
Its goal was to measure the physical layout of the beach's notorious headland rip current across a range of different swell, tidal and wind conditions.
The results revealed a pair of headland rips that drained the beach from each end, and several open coast rips between.
Surprisingly, about half of the drifters dropped into the headland rip floated off in a completely unexpected direction, SLSNZ national life saving manager Allan Mundy said.
One of Mt Maunganui's main rip currents ran alongside Leisure Island, at the far southern end of the beach. Photo / Alan Gibson
"That really informed us that we don't know as much as we thought we knew about rips."
Mt Maunganui was one of a growing number of beaches around the world now known to feature circular currents.
"Traditionally, we thought rips just go straight out to sea and you end up in Chile, but now research has shown a significant number actually circulate back to shore," said Mundy, who presented the findings to the World Conference on Drowning Prevention held recently in Vancouver.
"It has informed us that the old adage of swim to the side of the rip may not be, in three quarters of the cases, the best option."
Doing so could be dangerous anyway, he said, as just being told to swim out of a rip could trigger panic.
A rip current study at Mt Maunganui's Main Beach revealed a pair of headland rips that drained the beach from each end of it, with several open coast rips existing between. Photo / File
"And when someone is panicked, you've got literally seconds before they die - that's the cold hard facts of it.
"However, if someone floats on their back, the odds are they can raise their hands and we've got time to get [help] to them, but there's also a strong possibility that they might actually drift back into shore.
"So, looking at the past 18 months' evidence, we're actually saying, okay, we need to re-think the messaging out to the public."
Waikato University researcher Associate Professor Karin Bryan, who assisted with the study, said the Mt Maunganui findings were in line with those of a separate drifter-based project at Tairua in Coromandel.
"Looking at the last 18 months' evidence, we're actually saying, okay, we need to re-think the messaging out to the public," SLSNZ national life saving manager Allan Mundy says. Photo / File
"Unless you are very confident in the surf, just near the headland is usually the worst place to swim, with strong consistent rip currents," Bryan said.
"The good side is that they are strongly steered by the shape of the headland, so their direction is usually very consistent."
Rip currents along Main Beach tended to blend into the along-shore current, so if a swimmer was picked up by a strong along-shore current, they could be sure that, at some point, they would be delivered into the feeder of a rip.
"The water has to flow somewhere, and will pick the path of least resistance, so as soon as that current encounters a small bar or mound of sand, it will get re-directed seaward."
SLNZ was working through the findings with Water Safety New Zealand, and Mundy said there was appetite to take the study further.
Drifters were this month being distributed to other clubs, which would use them to collect data on local rips for a new national database.
