Rip current
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- Riptide redirects here. Riptide may also refer to an American TV series.
A rip current is a strong flow of water returning seaward from the shore. It is also called a "rip tide" or "riptide", or colloquially simply a rip. Rip currents typically flow at 0.5 metres per second (1-2 feet per second), and can be as fast as 2.5 metres/second (8 feet per second). They can occur at any beach with breaking waves, including the world's oceans and large lakes such as the Great Lakes in the United States and Canada.
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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 14 April 2004, an 18-year-old university student was killed by a rip current simply by standing in waist-deep ocean water at La Jolla Shores, near San Diego, California, USA. This occured at low tide after midnight (no lifeguards present), and unfortunately, he was a non-swimmer without a flotation device.
Rip currents cause approximately 100 deaths annually in the United States, more than all other natural hazards except heat. About 80% of rescues by surf beach lifeguards are due to rip currents. 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 water; this is not true.
Causes and occurrance
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. This water streams along the shoreline until it finds an exit back to the sea. The resulting rip current is usually narrow and located 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.
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.
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.
Safety tips
Posted warnings, where available, should always be heeded. It is advisable to stay at least 100 feet away from piers and jetties. 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 low tide--especially at night.
External links
- Rip Current Safety (US National Weather Service) (http://www.ripcurrents.noaa.gov/)
- United States Lifesaving Association, Rip Currents (http://www.usla.org/ripcurrents/default.asp)
- Undertow myth (pdf) (http://www.alisonosinski.com/pdf/pool_tip_12.pdf)