Baywatch's rips & recues.

As Baywatch guards rescue each other from emotional turmoil, their real-life counterparts deaf with the dangers of the ocean every day.

Dark storm clouds cruise over the horizon as Kim Drake, 20, keeps watch from her lifeguard tower on Huntington City Beach, Calif. She's glad the beach is empty. Although the wind is up, she spies flat, muddy water beyond the surf--a telltale sign of trouble.

Suddenly, Drake spots a woman and four pre-schoolers puttering toward the waves. As they wade in to their knees, Drake peels down to her swimsuit. She knows how deceptive--and powerful--the sea can be.

Within seconds, the toddlers are literally swept off their feet and pulled into deep water. The current (moving water) is fast, but Drake is faster. She rushes into the waves with her buoy and leads them back to shore.

It sounds like a scene from Baywatch, but what grabbed the pre-schoolers is a serious, real-life threat to ocean swimmers. It was a rip current--a fast-moving stream of water that runs back through the waves and heads toward the ocean. And rips aren't the only kind of water power Drake must contend with every summer. The crashing surf and backwash (backwards pull) from waves also make her job anything but a "day at the beach."

RIPPED AWAY

Of all beach dangers, rip currents are the scariest: they're to blame for 80 percent of lifeguard rescues. The 3A meter-wide (10-12 feet) streams of water can speed out to sea at up to 10 kilometers per hour (6 miles per hour). That's faster than most people can swim. Even experienced swimmers can find themselves helpless in a major rip.

Where do lifeguards look for these devilish currents? Often, the currents form between a tall, breaking (crashing) wave and a short, unbreaking wave that are side-by-side, heading to shore. (see diagram below.) But you'd have to look underneath the waves to find the real reason for the rip: a raised area of sandy ocean floor, called a sandbar.

The water above the sandbar is shallower than the water next to it. And shallow water causes an incoming wave to rise, "trip," and break; waves don't break in deep water.

"The shallow water over a sandbar causes one wave to break . while the one next to it continues toward shore," says Robert Dalrymple, a coastal engineer at the University of Delaware. The water dumped by that breaking wave rushes back out to sea through the spot between the tall wave and the short wave. That rush of water is the rip current.

Sometimes, violent waves can tear out a chunk of the sandbar. And the most powerful rip currents occur through such a gap. The rip current flows through that gap out to sea. Because fluids travel, faster when squeezed through a narrow channel, the rip can speed up and become even more deadly.

To find rip currents, guards hunt for a cloud of muddy water beyond the breaking waves. That cloud indicates where the rip ends. "It's brown and sandy because the rip current kicks up the sandy ocean bottom as it goes oat," explains Chicago lifeguard Joe Pecoraro. But rips are mis-chievous; they can appear at random, last for a few minutes, and disappear as suddenly as they came.

"CURRENT" RESEARCH

Because rip currents are so unpredictable, scientists haven't been able to measure them often.

So, instead of trying to track real rip currents, Dalrymple and his colleagues make them--in a lab. They use a square tank 18 m (60 ft) wide. The tank is 1 1/2 m (5 ft) deep at one end and has a sloping "shore" at the other. Concrete "sand bars" are built into the "ocean floor."

Thirty-four paddles send waves rolling across the water tank. When a rip current forms in a gap in the sandbar, Dalrymple places acoustic meters in the stream. Like police radar guns, the devices bounce sound waves off specks of dirt in the water. By measuring the waves that bounce back to the instruments, Dalrymple can tell how fast the rip is going.

"We're trying to understand the physics of how waves generate rip currents," Dalrymple says.

So if you get stuck in a rip current, are you a goner? Not if you know how to beat a rip. Don't swim against the current and head straight back to shore. "That's like swimming upstream; it tires you out and gets you nowhere," says Dalrymple. Instead, swim a short distance parallel to the beach, to get out of the rip current. Then head back to shore.

A WAVE TO THE GRAVE?

Even when rips are absent, the waves themselves can be treacherous. The energy released from a wave breaking on the beach has enough force to kill--up to 520 kg (1,150 lbs) of weight per cubic foot of water. If you've ever been hammered by a particularly nasty wave, you know what this energy can feel like.

Waves get their incredible power from the wind. Ocean waves start when a gust blows across the ocean's surface. The energy from the air is transferred to the water.

When a wave hits the shore, it flows up the sand until all of its energy is released. The water then drains back down the slope and into the ocean. If you've been pulled a short distance back out to sea after floating on a wave, you've felt the pull of that backwash. Backwash can yank you back with nearly as much force as the wave had when it first slammed onto the beach.

Most people call that backwash undertow, but that's actually incorrect. Undertow is really a much slower, subtle current heading out to sea. Swimmers swept out to sea often blame "undertow" when the real culprit is a rip current.

Despite these dangers, life-guarding is a rewarding job, says Florida guard Joe Securo. And you can't beat the working conditions. But Drake and Securo aren't too interested in the TV trials and tribulations of Baywatch beauties. They deal with enough real-life situations every day at work. "You should never underestimate the ocean," Drake says. "It has immense power."