Drones, 'drifters' to map deadly rip currents

Surf Life Saving New Zealand national lifesaving manager Allan Mundy with a drone and GPS-tracking "drifter" being used in a series of rip current surveys this summer. Photo: Supplied

Drones and GPS-tracking dummies are being deployed at Kiwi beaches to boost our understanding of the country's deadliest rips.

Surf Life Saving New Zealand (SLSNZ) has partnered with global antivirus software company Emsisoft for a project mapping currents and rips at beaches around the country.

The information gathered will improve current predictions used during searches, leading rescue teams to lost swimmers much faster, and help set a data standard for future research at other sites.

The project, kicking off with a trial run at Piha Beach this month, will draw upon floating GPS-mounted devices called "drifters" and drones to accurately map the dynamics of headland rip currents across a range of different swell, tidal and wind conditions.

Rips remain one of the biggest dangers to people on the country's coasts; seven people drowned last year after being caught in rips, and around 85 per cent of the average 1200 rescues lifeguards make each year involve them.

Previously, data on currents has been mapped from 500m offshore and it's expected the new insights will offer a much better understanding of how the rips work at different locations.

"If someone should get swept away in a rip, having the knowledge and understanding of the currents in that particular location will help narrow down the search area," SLSNZ national lifesaving manager Allan Mundy said.

The six-week surveys would involve lifeguards and Coastguard New Zealand personnel deploying and retrieving the drifters, which were designed to replicate a swimmer in a rip.

"Half of the drifters will be modified so they will sink below the water's surface to mimic how a body behaves once it becomes submerged after a drowning," Mundy said.

"This data will be priceless as it will help searchers better identify where to look for lost persons in the benthic current [the current on the bottom of the sea floor] which we don't currently have data on."

Dyes and similar drifters used in the past had only been observed within surface currents, which often flowed in very different directions to the currents on the sea floor.

Annual figures show popular Coromandel destination Hot Water Beach was the scene of the most surf rescues last season, nine more than Whangamata (72) and 12 more than Auckland's notorious Piha (69).