What is a rip current?
A rip current is a relatively small scale current of water flowing away from the beach.
Rip currents along the Sleeping Bear Dunes near Traverse City, MI. Courtesy of the University of Michigan
Coastal Engineering Department
How do rip currents form?
Rip currents develop when there is an uneven distribution of water onshore. The uneven distribution could be caused by varying wave heights, varying wave periods (how often the waves come onshore), varying wave directions, or shoreline structures. As winds blow over the lake and generate waves, the waves move towards the beach and crash onto shore. Uneven distributions of water will cause areas of high pressure and areas of low pressure in the water. Fluids flow towards low pressure (in the atmosphere and water). As an example, think of what happens in the bathtub when you open up the drain. The water will flow into the drain (area of low pressure). The same thing happens on the beach, except the water converges and heads OUT towards the lake (it cannot go down).
Areas of high and low pressure develop on the water surface, leading to convergence and eventually an outward flowing
current of water, known as a rip current. Image from the COMET Program.
Different Types Of Rip Currents
Structural Currents: A type of rip current that develops near a shoreline structure, such as a pier or breakwall. This current is discussed separately to clarify escape routes, since the classic rip current escape route does not work in these situations. This current is the most commonly observed current on the Great Lakes. To read about structural currents, go HERE.
Classic Rip Currents
Sandbars help to 'pile up' water along the shoreline, leading to the areas of high and low pressure discussed earlier. Once the water piles up along the shore, rip currents can develop in weak spots on the sandbar, or in already formed rip current channels.
As the water unevenly piles up between the shoreline and the sandbars, rips develop in the sandbars
from the increasing water pressure. Unsuspecting swimmers can be pulled out in the rip current.
Image is from the COMET Program.
Rip currents [seen in areas of the muddy/sandy looking water] flowing perpendicular to the shore at the Grand Sable Dunes, near Grand Marais, MI
Photo courtesy of Don Rolfson
Image showing Lake Superior near Grand Marais, MI. Note the complex sandbar structures along the shoreline conducive
to rip current development. Satellite Image from Google Maps, 2011.
Escaping from Classic Rip Currents
Escaping a rip current can be challenging, especially in the Great Lakes where waves often approach the shoreline in a rapid succession, further impeding swimmers. To escape a rip current, swim parallel to shore (out of the current), then try to swim back to shore. NEVER SWIM AGAINST THE CURRENT! Valuable energy is wasted on trying to fight the current.
River Mouth/Outlet Currents
A third type of rip current is associated with the mouths of rivers on the lake, or other drainage areas (such as a powerplant outlet). The water exiting the river mouth is enhanced and goes out into the lake (as a rip current). This is also enhanced by the longshore current if it is in place, serving as a "feeder" into the rip current.
This photo is of Au Train Michigan. Rip currents associated with river mouths
and complex sandbars have caused incidents here. Image is from Googlemaps.
Escape Method for Classic/Outlet type Rip Currents
Escaping from an outlet type current is the same as escaping a classic rip current-swim parallel to shore to get out of the current, then swim back to shore at an angle towards shore.
What ISN't a rip current?
There are many 'misnomers' for rip currents. The most common misnomers are "Undertow" and "Rip Tide." See the most common misnomers and their true definitions (taken from the NWS National Rip Current Page):
Undertow: Scientists actually have no agreed on definition of undertow. Many people assume it is an underwater current that sucks people downward....however this is not the case. In fact, there is no force in the lake or ocean that is found in the nearshore environment that will pull unsuspecting swimmers underwater! Undertow is thought to be the backwash after a wave crashes on the beach. This can trip waders, move them seaward, and make them susceptible to immersion from the next incoming wave. This would make the swimmer feel as if they are being "pulled under."
Rip Tide: The word tide inplies the pull of the sun or the moon. Rip Tides are NOT THE SAME AS RIP CURRENTS. They occur during high or low tides and are found in areas where water moves through inlets, mouths of estuaries, harbors, and embayments as well as around points of land and islands.
Rip currents develop as a result of uneven distributions of water in the surf zone. As a result, rip currents commonly develop near river mouths, shoreline structures, and at beaches with complex nearshore sandbar structures. The public should take precautions when they attend the beach, noting what type of hazards could be in the area.