What is a Rip Current?
Rip current at Carolina Beach, NC on
Sept. 11, 2001. Picture courtesy of
Carolina Beach Police Department.
A rip current is a strong but narrow current
flowing away from the beach. Rip currents
can occur any time of the day or year, but
are strong under certain tidal, atmospheric
and oceanographic conditions.
Rip
currents are not unique to North Carolina
or even the United States East Coast.
They can form at any beach with breaking
waves, including the beaches along the
Great Lakes.
The speeds within a rip
current can exceed 6 mph, which is as fast
as an Olympic swimmer!
This is one
reason why they can be dangerous.
A long swim back…
Some of the strongest rip currents can extend off
the coast the length of a football field (100
yards)! A swimmer who rides a rip current to the
sandbar can find they have a long swim back to
the beach.
There are three parts to a rip current: feeder
(one or two of them), neck, and head. The
Feeder portion is where the part of the current
that feeds into the rip current. Some rip currents
have one feeder, but they can have two.
AP - Michael Phelps
The Neck is the strongest part of a rip current and as a result is the most
dangerous part. Speeds within the current may be fast enough to pull
swimmers away from the beach very quickly. In fact, this is the portion of
the rip current where speeds can exceed 6 mph. The width of the neck is
typically 30 feet or less.
The final part of a rip
current is called the head.
The feeders flow into the
neck and the current in the
neck weakens in the head
are. In the head, a rip
current spreads outward
and dissipates. People who
get out in this portion of
the rip current find they
have a long way to swim
back to shore!
How Do Rip Currents Form?
Water in…water out…
Rip currents form when breaking waves pile water (onshore mass
transport) onto the beaches. The amount of mass transported to the
beaches must equal the amount of mass transported back into the
ocean to be in equilibrium. A transport mechanism back to the ocean
is a rip current.
The path of least resistance
After washing up on the beach, the water has no where to go other
than flow back into the ocean as a result of gravity. The water flows
seaward through paths of least resistance, which are typically breaks
in the sand bar. The strength of the rip currents is dependent on the
amount of incoming wave energy and the tide level.
Typically, the larger the breaking wave the stronger the rip currents
will be. Likewise, when there is less room over the sand bars for the
returning water to flow, the flow will become focused/faster along the
breaks in the sand bars. Therefore, rip currents are stronger and
more common a few hours either side of low tide. When the tide is
high the water returning from the beach has more room to flow back
across the sand bars and is less focused in the breaks between sand
bars.
As a result, stronger rip currents typically occur when large breaking
waves occur in the surf and when the tide is within a few hours either
side of low tide. It should be reiterated that rip currents can occur any
time during any day, regardless of the tidal cycle.
How to Spot a Rip Current
First, let a trained eye spot it!
When you arrive at the beach you should ask the lifeguard if there are
any rip currents. If there are no lifeguards at the beach you should
take a few moments to look at the surf to try to identify any rip
currents.
Rip currents are often very difficult to spot in the surf. But sometimes
there are a few telltale signs to look for including:
1) If the water is clear a rip
current may appear darker than
the surrounding water. This darker
water will help you identify where
the break in the sand bar is and
where a rip current will likely be
located.
2) Turbidity within a rip may give
the current a dirty or muddy
appearance. This occurs since the
rip is carrying sediment away from
the beach and is an excellent clue.
Photo courtesy of Chris Brewster, USLA.
Note the rip current (left of the person
near the surf) flanked by breaking waves.
3) There may be a foam neck
visible, especially if the conditions are rough.
4) In areas where waves do not break and are flanked by breaking
waves may signify a rip current.
5) There may be seaweed or the water
itself may be seen heading seaward.
Photo courtesy of Dr. Wendy Carey,
Delaware SeaGrant. Note the foam
next extending out into the surf.
Additional Tips: Look at the water
with polarized sunglasses. These types
of sunglasses will reduce glare, and
help you spot a rip. Do not hesitate to
ask a lifeguard where rip currents may
be located. Lifeguards are very familiar
with their beaches, including where a
rip current may develop or already
exists.
Why are Rip Currents Dangerous?
Can you spot this rip current?
Rip currents can be very difficult to
identify in the surf, especially from
ground level. If the surf is very
rough,
then
even
experienced
people have a hard time identifying
where the rip currents are.
The
reflection of sunlight on the ocean
(depending on the time of day) may
also make the detection of rip
currents difficult.
Yes there is a rip current in this picture!
Photo courtesy Carolina Beach Police
Department September 11, 2001.
Good weather ≠ safe surf!
Dangerous rip currents can often occur in otherwise good weather.
Just because the weather is nice at the beach, people incorrectly
assume that surf conditions will be nice too. Some of the most
dangerous rip current events occur when there is a hurricane far off
the coast, while at the beaches the weather is beautiful. People do not
realize that powerful swells generated by the hurricane will affect the
beaches, causing dangerous rip currents.
Many rip current casualties are those with little experience swimming
in the surf, and who might not even know what a rip current is. The
most important thing to remember is that you can’t out-swim a rip
current! Remember, it might be moving faster than an Olympic
swimmer.
Most rip fatalities occur because the victim becomes
exhausted trying to swim directly against the current.
The Four Rip Current Types
There are a few types of rip currents have been documented, and each type can
occur along the beaches of the Carolinas. The rip current types are: Fixed,
Permanent, Flash, and Traveling.
Fixed rip currents typically occur along beaches where
there are no man-made or natural structures such as
piers, rock outcrops, or jetties. Typically, there is an
area in the surf 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. These types of rip currents will
only remain fixed in one location until the near shore
bathymetry changes. These changes are usually a result of weather or seasonal
changes of the beach.
The Flash rip current is a very short duration (less than 10 minutes) 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 develop.
Permanent rip currents are nearly stationary seaward
currents that are focused on structures, thus can 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.
Fishing piers are additional structures which focus rip
currents. In this case, the rip is found aligned along or
under the pier.
The last of the rip current types is called a Traveling rip. This rip current is most
common when there is a sufficient long shore current (a current that moves parallel
to the beach) present to push the rip away from the location it originally developed.
As the rip current migrates away from its source area it weakens. If wave and tide
conditions continue to support rip current development, then a new one will form in
the source area and begin to move down the beach until weakening. This process
can continue throughout the day if conditions are just right.
Most times these rip currents are weak. However, if the wave energy coming into
the beach is significant and tide levels are just right, then any of these rip currents
can become strong and dangerous.