What is a riptide? Phenomenon explained after Bournemouth deaths

Locals are still reeling from the death of two children last week on a crowded beach in Bournemouth.

Sunnah Khan, 12, and Joe Abbess, 17, drowned on May 31 after reportedly being swept off a sandbar while eight other beachgoers got into trouble in the water.

Although Dorset police have yet to find out exactly what happened, a father of one of the survivors said his daughter was a beachgoer who was carried by a ‘riptide’ at the pier.

Although unconfirmed, Dorset Police said an investigation is ‘looking at all conditions’, including weather, wind and water conditions.

Here, MailOnline looks at the science behind the phenomenon – and the best course of action if you ever get caught up in it.

WHAT IS A RIPTIDE?

Rip tides, more accurately known as rip currents and also referred to simply as “rips,” are fast-moving channels of water that move away from the coast into the open sea.

They can reach speeds of up to five miles per hour – faster than an Olympic swimmer – making them a major fire hazard for all beachgoers.

The National Weather Service explains, “Rip currents occur when waves break close to the shoreline and build up water between the breaking waves and the beach.

“One of the ways this water returns to the sea is by forming a gulf stream, a narrow stream of water that quickly recedes from shore, often perpendicular to the shoreline.”

Although a father of one of the survivors said his daughter was carried by a “ripple current,” the more accurate term for this type of current on beaches is simply “ripple currents.”

Gerd Masselink, a professor of coastal geomorphology at the University of Plymouth, told MailOnline: ‘Rip currents are often referred to as rip tides – this is an incorrect term and we have been campaigning for decades to get rid of the term, but to no avail . .’

Professor Masselink is part of a research project looking specifically at rip currents in Bournemouth – which are common there – and their relationship to coastal structures.

“They mainly occur when the wind blows along the beach and the waves crash against the shore,” he told MailOnline.

“This generates coastal-parallel currents that are deflected seaward when they encounter perpendicular coastal structures, such as groynes and piers, resulting in seaward-flowing currents.”

Chris Brewster, retired chief lifeguard for the San Diego Lifeguard Service, agreed that the term high tide is a “misnomer” because “currents are not caused by tides.”

“That was an old belief that has been disproved,” he told MailOnline.

“Most of the time rip currents will occur wherever there is a jetty, pier or other structure and there are waves.”

WHAT DO RIP CURRENTS LOOK LIKE?

Rip currents can be seen from afar, so if you’re on a beach it’s worth checking out the surf zone before entering the beach.

They are much like a road or river running straight to the sea, like a strip of blue between the crashing white of the waves.

There is a noticeable break in the pattern of the waves where there is a rip current, although this is best seen from a high vantage point – which is why lifeguards sit in high ‘tower-like’ chairs.

ARE RIP CURRENT CAUSED BY BOATS?

Dorset police released a statement the day after the incident in which a man was said to have been arrested ‘when on the water’ on suspicion of manslaughter, although he has since been released for investigation.

His release comes after officers seized a cruise boat called The Dorset Belle and placed it under guard at Poole Harbour, five miles from Bournemouth Pier, from where he usually sails.

It has not been confirmed if a rip current occurred last Wednesday or how it was related to the pleasure boat detained by police, the Dorset Belle.

‘Insiders’ have suggested that the ‘sudden riptide’ may have contributed to their deaths and could have been caused by the boat.

A source told The sun: ‘They were on a sandbar east of the pier when the Dorset Belle moored alongside the pier.

“It created a tidal wave that engulfed everyone on the sandbar and basically forced them further out to sea.”

However, according to Professor Masselink, boats do not cause wave motion; rather, they are formed by the natural interaction of the water.

WHY ARE RIP CURRENT DANGEROUS?

Rip currents can drag even the strongest swimmer out to sea and result in death, as those caught in them try to resist.

In a Gulf Stream, panicked swimmers often try to counter this by swimming back to shore, risking drowning due to fatigue.

‘The danger arises when an ill-informed swimmer uses an inadequate strategy to escape the rip, such as fighting directly against the current,’ says Dr Sergio Maldonado, an expert in environmental fluid mechanics at the University of Southampton.

‘This can lead to fatigue, panic and in some cases drowning.

“Swimming straight into the rip can require several times more strength from the swimmer than other strategies advised by lifeguards.”

According to the American Boating Association, a rip current is usually strongest about a foot from the bottom of the water.

As a result, a person’s feet can be knocked out from under them, making it feel like something is pulling underwater from below.

HOW TO SURVIVE A RIP STREAM

The best way to escape a rip current is to swim parallel to the shore rather than towards it, and above all to keep calm.

Swimming back to shore simply means you’re swimming into the rip, which tires you out and can lead to drowning.

Alternatively, drifting with the current can take you back to a sandbar – a deposit of sand that forms a shallow area in the sea.

The National Oceanic and Atmospheric Administration gives the following advice if you ever find yourself in a Gulf Stream: “Don’t fight it. Swim parallel to the shore and swim back to land at an angle.’

The best way to avoid rips altogether is to choose a beach with lifeguards and always swim between the red and yellow flags, which are marked based on where it’s safer to swim in the current conditions.