Rip Currents, Riptides & Longshore Drift For Surfers
How rip currents work, why they're not riptides, and what you should do if you get caught in one
Rip currents are responsible for around two thirds of all rescues carried out by RNLI lifeguards in the UK; in Australia, they're deadlier than cyclones, bush fires, floods, and shark attacks combined. Rip currents can be killers -- but they're generally speaking harmless to those who know what they're up against. So whether you're learning to surf or just spending the day splashing around at the beach, it's essential you understand how rip currents work, what to do if you get caught in one, and why those who call them riptides are gravely, gravely mistaken.
What is a rip current?
A rip current is a body of water moving back out to sea, and often dragging unsuspecting swimmers and surfers with it. When water is pushed towards the shore by waves — which break over sandbars, where the water is shallower — it flows back out to sea following the path of least resistance. This path consists of gaps in the sandbar, in between where the waves are breaking. Rip currents can be identified by waveless channels of rippled, possibly discoloured water — they look a bit like rivers, basically, flowing out through the surf zone. Often, noticing the lack of waves and thinking it the safer or less challenging option, inexperienced beach-goers will choose to swim exactly where a rip has formed.
In shallower water, the flow of water will sometimes travel parallel to the shore, towards the main channel of water directed seawards. In the anatomy of a rip current, this is known as the “feeder", and is essentially the water seeking out that gap in the sandbar where it can escape back out to sea. As the main channel of seawards flow (sometimes called the “neck") passes beyond the breaking waves, it loses impetus, mushrooming into the “head" as the flow of water slows down.
How fast are rip currents?
Typically rip currents move at around 1-2 mph, but they’re capable of reaching speeds of around 4 mph, which is as fast as an elite level swimmer.
What should you do if you get caught in a rip current?
Bearing in mind the above, the worst thing you can do when stuck in a rip current is panic and/or try to swim or paddle directly against it; this almost invariably fails, and leads instead to fatigue, which is when rip currents become dangerous and lead to drownings. If you’re able to touch the bottom then wade your way to safety, otherwise paddle at a perpendicular angle to the flow of the rip current (parallel to shore). You will soon find yourself out of the rip and in a position to return safely to shore. If you have one, always keep hold of your surfboard for buoyancy; if you feel like you’re not making any headway and might be getting into real trouble, wave one arm to attract attention — this is the universal distress signal.
A rip current doesn’t keep going out to sea indefinitely but disperses and peters out once it’s past the surf zone, at which point paddling to the side and catching a wave back to shore should be simple. In other words, holding tight and letting the rip current run its course isn’t as disastrous an idea as it might sound. DRIBS (Dynamics of Rips and Implications for Beach Safety), a new project set up by the RNLI in conjunction with the University of Plymouth, has a great website providing plenty of more detailed technical information.
Can you use a rip current to your advantage?
Yes, once you are competent enough to navigate your way around the surf zone comfortably. Rather than paddling out through the breaking waves and being repeatedly pushed back towards shore, experienced surfers may actively seek out rip currents as a more efficient route for getting out into the line-up.
And what’s longshore drift?
Surfers often complain about strong “rips" that flow laterally along the shoreline and require them to paddle constantly. In fact, such currents are more accurately described as longshore drift or longshore current (the defining characteristic of a rip current is that it goes out to sea). While rip currents are localised, longshore drift is general, moving in the same direction along a whole coastline. This poses little danger in itself, but can drag surfers towards hazardous obstacles (rocks, groynes, piers, etc.) without their noticing, or simply away from supervising family members and friends. If you find yourself moving swiftly in the direction of an immovable object, return to shore sooner than think you really have to, leaving yourself a decent margin for error. Bear in mind that around piers and groynes, the current is often significantly stronger, and often impossible to escape from (see below).
Generally speaking, the larger and more powerful the surf, the stronger the longshore current is likely to be, although this isn’t the only factor involved, and the longshore current can be negligible on even the biggest of days. Swell direction, for instance, plays an even larger part, longshore current tending to result when waves strike the coast at an angle. Often wind and the movement of the tide will also have a bearing both on the longshore current’s strength and its direction.
When longshore current comes up against an immovable obstacle -- a headland, a group of rocks, a groyne, a pier -- it is deflected seawards. This is known as a topographical rip and will run parallel to the obstacle, dragging anybody caught in it out to sea. Add waves and the original longshore flow to the equation and the chances of getting washed onto, or entangled in, the obstacle in question are high.
What’s a riptide?
Generally speaking, a misnomer. People tend to say riptide when what they really mean is a rip current; currents and tides are two fundamentally different phenomena, and though the tide may a peripheral role in the formation of a rip current, it is never its main driving force. An actual riptide would be a strong tidal flow of water within an estuary or other enclosed tidal area. Say riptide when you mean rip current and lifeguards get extremely upset.
What’s an undertow?
Another frequently misused and misunderstood word, undertow is the return flow of waves breaking on the shore, and occurs under the surface of the water (this is what the under part refers to; the direction of flow is outwards, not downwards). Again, the term is often mistakenly applied to rip currents, but undertow is a general movement of water rather than one concentrated in a narrow channel, and is felt strongest in shallow water. It can still pose a threat, however, particularly when the surf is big, sweeping paddlers off their feet or complicating efforts to return to shore.
Rip currents likewise flow only in an offshore direction. Contrary to what some people think, they cannot actively pull someone underwater; if a swimmer struggles to stay afloat when caught in a rip current, it is due to exhaustion or panic or a simple lack of swimming ability.