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Why the rip current of the sea is dangerous: what it is, how to recognize it and behave

The return currents (or rip currents, sometimes improperly called rip currents) are a type of ocean current that forms when the waves are particularly intense and move from the beaches or coasts towards the open sea. They can be recognized by noticing a portion of blue sea in the middle of the white breakers of the waves, with a flatter and calmer surface than the surrounding water. They are dangerous for swimmersespecially in summer when the beaches are more crowded, due to their apparently calm appearance and because they are fast enough to carry a person away from the coast to areas where the seabed is deeper. In Italy alone, approximately 300 deaths by drowning due to return currents in the period 2016-2021Knowing how to recognize them and how to behave is therefore important for our safety and that of our loved ones, especially during summer holidays in seaside resorts.

What is a return current?

As the name itself suggests, the return currents they are fairly rapid flows of water (up to 2.5 m/s, i.e. 9 km/h) that cause the water carried to the shore by sufficiently energetic waves to “return” to the open sea. They are rather narrow, with typical widths of a few metres, and a few dozen metres long. They generally appear as a “neck” of apparently calm water on the surface that can interrupt or “dig” the Breakings of the waves (that is, the white foam on their top, so to speak) and then disperse in the so-called “head” of the currents beyond the line of the breakers.

How ocean rip currents form

These dangerous currents can form in the presence seabeds that are neither too flat nor too steepwhere the “shoal” (i.e. the area where the seabed suddenly rises) has an interruption. When the sea is quite rough and the waves are quite energetic, the breakers form in correspondence with the shoal and the waves can “collapse” forward, towards the shore. At this point, a build-up of water is created on the coastline and, to restore the balance, this water must return to the open sea. This is not a problem as long as the shoal has an interruption: in those points, in fact, the greater depth of the seabed creates the perfect conditions for a rapid channeling of the water. The excess water thus converges from the surrounding areas through currents parallel to the coast (the tributary currents) and here the return current is formed.

Diagram of the formation of a backflow current. Credit: Backcomp.gif: National Weather Service, Wilmington, NCderivative work: Xander89, CC BY–SA 3.0, via Wikimedia Commons

Inflowing currents can also form spontaneously in correspondence with promontories surrounded by circular bays: in these cases it is the geometry of the coast itself that creates the convergence of inflowing currents necessary for the formation of return currents.

back currents in Nova Scotia
Pattern of rip current formation in a promontory in Nova Scotia, Canada. Credit: WikiPedant, CC BY–SA 4.0, via Wikimedia Commons

The fact that there are return currents where the dryness breaks contributes to making them dangerousbecause in those points the seabed is deeper and therefore the risk of drowning increases.

How to recognize return currents

Given that typically the areas systematically affected by return currents are signalled by signswhat was said before helps us understand what clues to observe to recognize a return current and thus avoid ending up in it. The most important thing to pay attention to is the presence of an area of apparently calm sea surrounded by breakers tormented. This “apparent calm” can deceive swimmers, who will prefer it to the rougher waters around them. If you find yourself faced with a situation like the one shown in the photo below, with a portion of blue sea surrounded by white foam, avoid it.

rip current
Credit: US Army Corps of Engineers Field Research Facility at Duck, NC., via Wikimedia Commons

Return currents can also be recognized by the fact that on the surface the water does not follow the shapes of the surrounding wave motion and sometimes even from the fact that their water can be more cloudy compared to the surrounding one, since it collects sediments transported by the inflowing currents.

What to do to get out if you end up in it

Often being overwhelmed by a back current is an unexpected event that causes panic. It is therefore essential keep a clear head to behave in the best way. In fact, the instinct is to swim towards the shore, but this would only mean going against the current. If we were to find ourselves inside a return current, the best thing to do is, counterintuitively, to to be carried by the current: once the line of the breakers is passed the current ceases and at that point you can swim sideways – that is, parallel to the coast – until reaching the shoal. There you are safe and can ask for help or slowly reach the shore keeping away from the current.

Image
This sign in San Diego, California, explains what to do in the event of rip currents. Credit: Invertzoo, CC BY–SA 4.0, via Wikimedia Commons