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Rip Currents

Each year, especially during peak vacation times, many people fall victim to rip currents. Statistics show that rip currents can be deadly. These relatively small scale surf zone currents form under specific conditions and if these conditions are just right, a rip current can become very hazardous. In some cases, even the most experienced swimmers are in danger when they encounter a strong rip. However, the experienced swimmer knows WHAT TO DO to get out of danger. There are also several Visual Clues that may help you identify a rip current before you enter the water.

A rip current is a channel of water that flows away from the beach that has Three Main Components. The FEEDER portion is the main source of energy for the current. As waves breaks over the sandbar the water becomes trapped in the zone between the beach and the bar. The water is acted upon by gravity which seeks the path of least resistance, which is typically a break between two sandbars. The classic rip has two feeders while one feeder can also support a rip.

The NECK is the portion of the rip that makes up the higher velocity water that moves away from the beach. This is the most dangerous part of the rip. Speeds within the current may be fast enough to pull swimmers away from the beach very quickly. It is not unrealistic for rip currents to exceed 4 or 5 knots (faster than an Olympic swimmer) and have widths that range from 10 to 30 yards.

The final segment of the rip current, or where the neck ends is called the HEAD In the head area, a rip current becomes less focused and begins to spread outward. This occurs since the break between sand bars or length of a structure is limited seaward. As a result, the net seaward motion of the rip diminishes considerably the farther away from the break in sand bars or from a structure. People who get out in this area of the rip find they have a long way to swim back to shore.

Interestly, research suggests there are several types of rip currents. In fact, each type of rip current can be found along the Carolinas. The type-1 rip or Fixed rip occurs along beaches where there are no man-made structures. Typically, there is an area where the water is deeper than the surrounding water. They are found in one general location most times and are strongly influenced by surf conditions, as well as the shape of the coast and sandbar structure. A good place to find this type of rip is along an intermediate point of a cut(cusp) between two points along the beach.

The Type-2 rip or FLASH rip is a short duration current, which is enhanced by heavy surf. This is especially true when large swells from distant hurricanes increase the amount of wave energy and wave volume dispersed onto the beaches. Flash rip currents are extremely unpredictable, because of the temporary conditions they produce, as well as variable locations they set up.

The Type-3 rip or Permanent rip is defined as a stationary seaward current that is focused on structures, thus persist almost year round. Structures such as jetties, groins, or large drainage outflows will aid the formation of permanent rip currents. An example of a permanent rip current can be seen at the Fort Fisher revetment. This type of rip current can change in magnitude given surf/swell conditions. Fishing piers are additional structures which focus rip currents. In this case, the rip is found aligned along and under the pier.

The final rip current variation, the Type-4 rip or Traveling rip can appear to move down the beach aided by the prevailing wave direction. It has been documented that a strong and persistent swell begins the traveling rip process. Swells impacting one portion of the beach will temporarily enhance the rips there; however, once the swells become focused on another area the initial rips weaken while new rips strengthen in the new area. This type of rip current is strongest when the swell periods are very defined, allowing for an apparent propagation down the beach as additional sets interact with the coast.  

Several statistical studies imply that there is a direct correlation between tides and frequency of occurrence, particularly for the more life threatening rip currents. WFO Miami has found that there is a critical 6 hour period focused around low tide. This period ranges from 2 hours prior to low tide to 4 hours following low tide. Statistics from WFO Miami's beaches reveal that this time period has nearly four times as many rip current related fatalities than other tidal periods.

The higher drowning frequency during that time frame is likely due to "tuning" of the surf zone, where factors such as wave height and water level become enhancing factors. During low tide the volume of water passing by the sandbars becomes restricted due to decreasing water levels. Thus, the water will accelerate faster through breaks in the bars. This enhances the rips seaward velocity, making it increasingly dangerous to swimmers. This process will occur until a couple hours before high tide when the water level finally increases enough to compensate the seaward flow, thus weakening or disrupting the rip.

So the next time you go swimming pay attention for specific clues that may help you determine if a rip current is present. If you are not sure, then ask a lifeguard for surf conditions before you enter the water. Remember, if you get caught in a rip current DON'T PANIC. By remaining calm you can think clearly, and easily recall the steps you must take to make it back to the beach.

And finally... Remain Aware, Swim with Care

From your friends at the National Weather Service in Wilmington, NC

 


National Weather Service
Weather Forecast Office Wilmington, NC
2015 Gardner Drive
Wilmington, NC 28405
(910) 762-4289

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Page Last Modified: 14 January 2007 9:00 PM


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