Swimmers: Avoid trouble by studying currents

By Michael Tsai
Advertiser Staff Writer

It's a warm, clear autumn day and — clever you — you've somehow managed to clear a big enough hole in your schedule to sneak in a little swim at the nearby beach park.

It doesn't take long for your body to lock into that familiar rhythm. It's a really good workout: You're breathless.

At some point it occurs to you that you've been looking down at the same distinctive piece of coral for the past five minutes.You stop, lift your head and try to get your bearings. You look down again. That piece of coral is no longer beneath you. It's ahead of you and getting farther ahead by the second.

Seems you've been swimming against a current, and a strong one at that. What you do next will depend greatly on your experience as an open-ocean swimmer and your understanding of where it is you're swimming. A wrong decision now could be disastrous.

"Swimmers really need to know how and why currents develop at surf beaches," says Ralph Goto, ocean safety administrator for Honolulu's Ocean Safety and Lifeguard Services Division. "What you do when you get caught in a current depends a lot on what kind of current it is and what's around you."

Rough lesson

This year's Waikiki Roughwater Swim on Sept. 1 provided an unfortunate but useful reminder about the value of recognizing and preparing for dynamic ocean conditions.

The 2.4-mile swim from San Souci to the Hilton Rainbow Tower has traditionally been one of the most popular open-ocean events in Hawai'i. However, this year's race coincided with the approach of Hurricane Jimena south of the island chain, and uncertainty about the effect of the storm on ocean conditions prompted many would-be roughwater swimmers to skip the event.

Of the nearly 950 swimmers who started the race, more than 360 had to be rescued. According to race organizers, a record 590 people did not complete the race.

But it wasn't high surf or any other hurricane-related condition that caused the trouble, race organizers and ocean safety specialists agree. (A pre-race survey found relatively calm conditions on the surface of the water.) The culprit was an unusually strong but otherwise predictable outbound current that stalled hundreds of swimmers between the third and fourth markers.

Race director Joe Lileikis said the course intersects a naturally occurring tidal current which, in a daily cycle, delivers a huge volume of water westward and inland, then flows outward in the opposite direction. Race participants were apparently caught in the outgoing current.

"It's the kind of thing that could happen in any given year, hurricane or not," Lileikis said.

Know your current

Many of those familiar with the course identified the current early on and made the proper adjustments. Strong swimmers confronted it head on with the understanding that they would likely exceed their predicted finish times by several minutes. Others opted for a slightly longer route closer to shore, where the current wasn't as strong.

To understand how currents move, Goto said, it is first important to grasp one simple truth: Water has its own proper level, and when it exceeds that level, it will take the path of least resistance to correct itself.

That's the basic principle behind the most dangerous and most notorious of currents.

Rip currents, as described in the United States Lifesaving Association training text, are created when breaking waves push water onto the beach above the mean level of the sea. As gravity pulls the water back down, oncoming waves push additional water toward the beach creating a damming effect.

The accumulated water eventually finds the path of least resistance, such as an underwater trough. As this water rushes to a concentrated channel, a strong current is produced.

Some rip currents remain fixed in one place, usually because of underwater sand or rock structures that provide a stable channel through which water can move.

Others occur spontaneously in stormy conditions or high surf as an unusually high volume of water rapidly builds and exits. Another type of rip tide travels along the beach following the prevailing direction of the waves.

Rip currents can vary greatly in width, length and power, but even a relatively small one can be deadly to an inexperienced swimmer.

It is often useless to try to swim against a rip current. Some ocean-safety experts recommend swimming parallel or riding the relatively short currents out to the end, then swimming back to shore. (Surfers sometimes save their paddling muscles by riding rip currents back out to sea after a ride.)

Another current type common to Hawai'i is the longshore current, also known as a lateral current or a lateral drift.

As described in the USLA text, these currents run parallel to the beach and are often caused by waves approaching the beach at a diagonal angle, pushing water along the beach as they break.

Experienced ocean swimmers can sometimes identify currents on sight.

For example, rip currents may appear as a run of choppy water and may look darker than their surrounding waters. For others, knowing what sort of currents a beach has (lifeguards are good sources) might help in plotting appropriate responses.

Chris Moore, a longtime waterman and one of the organizers of the popular North Shore Swim Series, said making the proper call in an emergency situation involves understanding not just current or tidal conditions, but the underwater geography of the beach (where reef or channels are located, for example) and your own abilities and limitations.

"A lot of what you do depends on where you are and what the conditions are," he said.

Moore emphasizes that responsible swimmers will do whatever it takes to avoid putting themselves in danger in the first place. "You have to take responsibility for yourself and you can't expect to be rescued.

"Look at what happened with Eddie Aikau," Moore said, referring to the renowned Hawai'i surfer who died paddling his surfboard in stormy weather in an attempt to save the crew of Hokule'a after the voyaging canoe capsized. "That showed that even the best waterman in the world is no match for the ocean."

Reach Michael Tsai at mtsai@honoluluadvertiser.com or 535-2461.

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