Rip current
From Wikipedia, the free encyclopedia
A rip current is a strong flow of water returning seaward from the shore. It is often mistakenly called a "rip tide" or "riptide", though the occurrence is not related to the tides. Colloquially a rip current is known simply as a rip, or the misnomer undertow. Although rip currents would exist even without the tides, tides can make an existing rip much more dangerous (especially low tide). Typical flow is at 0.5 meters per second (1-2 feet per second), and can be as fast as 2.5 meters per second (8 feet per second). Rip currents can move to different locations on a beach break, up to a few hundred feet a day. They can occur at any beach with breaking waves, including the world's oceans, seas, and large lakes such as the Great Lakes in Canada and the United States.
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[edit] Recognizing a rip current
There are signs to look for in the water to see if a rip current is present. Rip currents can be recognized by unusually calm waters, caused by the channel of water flowing out. The color of the water may be different from the surrounding area. Also, the waterline is lower on the shore near a rip current. It is advisable to look for the existence of a rip current before heading into the water.
[edit] Uses
Rip currents can also be extremely useful for surfers as they save the effort of having to paddle out to catch a set. They can also be used by lifeguards (swimming or on paddleboards), who can use them to get out from the shore to perform a rescue much quicker than they could by swimming/paddling through the waves.
[edit] Dangers
Such currents can all be extremely dangerous, dragging swimmers away from the beach and leading to death by drowning when they attempt to fight the current and become exhausted.
Although rare, rip currents can be deadly for non-swimmers as well: a person standing waist deep in water can be dragged out into deeper waters, where they can drown if they are unable to swim and are not wearing a flotation device. On April 14, 2004, Daniel Cho, an 18-year-old university student, was killed by a rip current simply by standing in the ocean water at La Jolla Shores, near San Diego, California, USA. This occurred at low tide after midnight (no lifeguards present), and unfortunately, he was a non-swimmer without a flotation device.
In another occurence on Sunday, March 11th 2007, two University of California San Diego students, Joseph Han and Michael Feng, found themselves in a near death experience as they were dragged helplessly hundreds of yards out by an unsuspected rip current. As professional bodysurfers enjoying a few waves on a hot day, Feng heard his friend's cry for help a hundred yards north from his location in the water. Suspecting some sort of injury, Feng, a certified Red Cross Lifeguard and experienced Eagle scout, swam over to provide casual help for his companion. Instead, they were sent into a spiral of panic as the current swept them further from shore. Describing one particular moment as a seven foot wave crashed over them, Han recalls: "I really felt like I would die right then. I was so exhausted from trying to swim back to safety." After approximately 30 minutes of swimming parallel to the shore and slowly making their way back towards the beach, now hundreds of yards away, Feng and Han arrived, out of breath and muscle-fatigued. "Their biggest mistake was originally trying to fight their way back to the shore," comments Michelle Park, an oceanography expert. "The most important thing to remember is that it is impossible to fight the current. It is simply too strong. Your best chance is to swim to the side, and slowly and calmly make your way back to the shore."
Rip currents cause approximately 100 deaths annually in the United States, more than all other natural hazards except heat. Over 80% of rescues by surf beach lifeguards are due to rip currents. When a rip current takes control of an unsuspecting swimmer, there is no chance for the swimmer to escape. A common misconception is that a rip occurring under the water, instead of on top — an undertow — is strong enough to drag people under the surface of the water. This is not true. To survive a rip current one can first cry for help, then let the current take you. When it lets up, swim out of its grasp and make your way back to the shore
[edit] Causes and occurrence
While the precise conditions leading to a rip current are not known, the general picture is as follows. When wind and waves push water towards the shore, the previous backwash is often pushed sideways by the oncoming waves. This water streams along the shoreline until it finds an exit back to the sea. The resulting rip current is usually narrow and located in a trench between sandbars, under piers or along jetties. The current is strongest at the surface, and can dampen incoming waves, leading to the illusion of a particularly calm area, luring some swimmers in.
Rip currents are stronger when the surf is rough (such as during high onshore winds, or when a strong hurricane is far offshore) or when the tide is low.
[edit] Surviving an encounter with a rip current
When caught in a rip current, one should not fight it, but rather swim parallel to the shoreline in order to leave it. If you see a person caught in one, yell at them to do so. Floating until the current disperses into deeper waters is another method of surviving such a dangerous incident, but it may leave the swimmer farther out from shore.
[edit] Safety tips
Posted warnings, where available, should always be heeded. It is advisable to stay at least 100 feet away from piers and jetties, which impede waves, encouraging rip currents to form. Also, check the local newspaper and internet for tide timetables. (Beware that tides can be substantially different at beaches relatively close to each other.) Never go into the water without lifeguard supervision from -2 to +4 hours of the daily maximum low tide -- especially at night.
