August 1, 2006 — Rip currents flow in very erratic patterns, not in steady courses as previously believed -- which may help explain why they can be so dangerous even for experienced swimmers. Oceanographers have discovered the behavior by tracking the motion of colored dye added to a wave pool generating rip currents.
NEWARK, Del. -- Each year, an estimated 100 people drown in ocean rip currents. A strong current can sweep even the strongest swimmer out to sea. Researchers are now making waves studying rip currents, revealing the life-saving information you need to know about these dangerous ocean currents.
There's something lurking in the ocean -- creating panic in even the best swimmers!
"It came really quick, like we went under a wave, and then the next thing we know it was just, like, pulling us out," says 18-year old Phoebe Brown. Not a shark, it's a rip current. And it can drag unsuspecting swimmers out to sea, up to eight feet per second.
Rip currents form at breaks in sandbars hidden underwater, creating a strong channel of water that pulls anything in its path far away from shore. Traditionally, oceanographers believed rip currents had a steady, uniform course. Now, new research shows the flow of water moves in an erratic pattern.
Oceanographer James Kirby, Jr, says, "Flow patterns get very, very complicated and very, very unpredictable, and we're trying to come to an understanding of what causes all that complication."
In a study at the University of Delaware in Newark, Kirby added colored dye to a wave pool generating rip currents. The dye's course is recorded as it moves through the current. The dye's movement shows an irregular rip current pattern -- making it more difficult to escape.
"It's very difficult for a swimmer once he's actually caught in the flow even to establish a sense of orientation and decide which way to swim," Kirby tells DBIS. He also says some rip currents can last for weeks and even months at a time, in the same location.
To avoid unpredictable rip currents, keep an eye out for signs of one, like broken wave patterns and discolored water. If you end up caught in a rip current...
"Number one is don't panic," says Jesse Steele, a lifeguard at Bethany Beach in Delaware. "Swim parallel to shore."
BACKGROUND: A professor at the University of Delaware has created a comprehensive computer model that predicts the physical processes in the area from the high tide mark on shore to a depth of 10 meters, called the nearshore ocean.Wave weight, current movement and naturally occurring sediment transport, are analyzed by computers to from a computer model. The model allows weather forecasters to quickly predict dangerous surf conditions and issue immediate warnings. It can even predict some dangerous events weeks before they occur. Swimmers and life guards have more tools to identify rip currents, for example. The model would also be useful for builders designing shore properties.
WHAT ARE RIP CURRENTS? A rip current is a strong flow of water returning seaward along the shore. When wind and waves push water to the shore, the previous backwash is often pushed sideways by the oncoming waves. The backwash streams along the shoreline until it finds an exit back to the sea. The resulting rip current is usually narrow and located in trenches between sandbars, under piers, or along jetties. The current is strongest at the surface and can dampen incoming waves, which might make the area seem deceptively calm. That's one thing to look for when searching for rip currents: unusually calm waters. The color of the water may be different from the surrounding area, and the waterline will be lower on the shore near a rip current.
IT'S NOT THE UNDERTOW: Many of the deaths resulting from rip currents are wrongly attributed to an undertow. The two are related, but distinct. Rip currents occur if there's a place along the beach where the incoming waves aren't as strong, so that the escaping water goes through that weak spot. If there is no spot with weaker surf, the accumulated water flows down and under the waves and back out to sea, forming an undertow.
TIDES AND THE MOON: Rip currents are sometimes erroneously called "rip tides." They are not tides, although particularly low tides can lead to stronger rip currents. What are tides? The strength of gravity depends on the distance from the source; the closer you are, the stronger the "pull" that you feel. The moon's gravity acts on the earth, but the diameter of the earth is large enough compared to the distance of the moon that one side of our planet -- the one nearer the moon -- feels the moon's gravity much more strongly than the side further away from the moon. In effect, the earth is "stretched" by the difference in the moon's gravity across the earth, and this gives rise to the tides. That's why there are two tidal bulges on the earth, one on the near side, and one on the far side.
SAFETY TIPS: The most common advice for escaping a rip current is not to panic and try to swim against the current directly back to shore. People become exhausted very quickly and can easily drown. Instead, you should swim parallel to the beach and then let the waves bring you into shore.
The American Geophysical Union contributed to the information contained in the TV portion of this report.
Note: This story and accompanying video were originally produced for the American Institute of Physics series Discoveries and Breakthroughs in Science by Ivanhoe Broadcast News and are protected by copyright law. All rights reserved.
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