WAVES & RIPS
In this extract from Coast Magazine [May 2019] William sheds light on the interconnected relationship between waves and rip currents.
When I think of the coast, waves race through my mind; flashes of brilliant white peeling across a dark blue sea, a cacophony of sound and spray as the ocean’s energy explodes at my feet. There’s a mesmerising quality to watching waves - especially when people are surfing them. It gives a sense of perspective, time and scale; a juxtaposition of movement as the surfer carves up and down the face, streaks of white trailing every turn as the fins slice through the water. But I can’t watch for too long because I want to be out there too, gliding on sea so clear it feels like you’re suspended in shimmering air, racing towards the shore with the power of nature at the tips of your toes.
This power comes from wind blowing over the sea. Friction transfers energy from air to water, starting with a ripple and growing into a powerful swell that travels across entire oceans. The longer and stronger the winds blow, the more powerful the swell becomes, allowing it to travel faster and further until it’s compressed by the shallow water around the coast. Finally, when the depth is 1.2 times the swell height, the waves break. This is one of the magic numbers when it comes to wave dynamics; my other favourite is that by multiplying the period of a swell [the time between two consecutive waves] by 1.5 you can work out its speed.
Above: Jayce Robinson [one of Britain’s leading surfers] giving waves a sense of scale off the coast of Cornwall, photographed by James Warbey
Observing how waves break can tell you a huge amount about the seabed. On beaches where waves break a long way out you can deduce that the water stays relatively shallow with a gentle gradient. In contrast, on beaches where the waves ‘jack up’ and break close to shore, there must be a steeply sloping seabed that suddenly goes from deep to shallow. Of the two, gently sloping beaches are better for less confident swimmers and children as you can safely stay within your depth. Furthermore, the shape of the seabed means these waves break gentler with shallow faces – much more family friendly than the vertical-faced and heavy-dumping ‘barrel’ waves of steep beaches.
Perhaps the most important clue waves give is to warn you of rip currents. The two go hand-in-hand; waves bring water in and rips take water back out to sea. Although rips fill many people with dread [they are the biggest killer around the coast of Britain], for surfers like myself they provide a fantastic highway ‘out back’ and we actively search for them and throw ourselves into their grip. After all, they’re simply a fast current taking you straight out beyond the surf zone, where they then fizzle out. What’s the point wasting energy paddling through relentless walls of whitewater when you could sit on a treadmill straight to your destination?
TYPES OF RIP
I first started using rips in Tynemouth, where one flows along the old tidal pool. This is a type of Obstruction Rip that can be found all around the British coast; waves break on the beach, water flows along the shore then hits the obstruction and gets deflected out to sea. The obstruction can be a wall, jetty, pier, groyne, cliff – anything solid that faces out to sea. This makes Obstruction Rips easy to spot, as you can’t miss the structure that creates them - which is a good thing because they are the most powerful type of rip current, travelling further out to sea with greater speed than their sibling the Deep-Water Rip.
Above: Plan view of an Obstruction Rip
Deep-Water Rips are more difficult to spot. They rush out to sea through channels of deeper water between the shallows where waves break; a gap between sandbars, a slice through a reef or a channel eroded by the flow of a river. Because the cause of a Deep-Water Rip is underwater, you’ve got to be more alert for clues on the surface; the water might be a darker blue [because it’s deeper] with more sediment [carrying sand from the beach] and calmer [because the waves aren’t breaking there]. Ironically, many people inadvertently head straight for Deep-Water Rips because they think the calmer water is safer than the crashing waves. Instead, they get taken out to sea at 2 metres a second and those who haven’t taken the time to learn about rips try to swim against the current [which is impossible], get exhausted, panic, then drown.
Above: Section view of a Deep-water Rip
On my Tide Walks I recommend people to find high ground overlooking the beach – dunes or cliffs work well – and spend a few minutes watching the waves and spotting rip currents. Remember that there are often multiple rip currents on a beach; sometimes a mix of Deep-Water and Obstruction, so keep looking after you spot the first. But sometimes they still catch you by surprise. Last summer I was on a west coast beach, standing in knee deep water and waiting for a gap in the swell to paddle out [I couldn’t see any noticeable rip currents to use]. A huge wave broke straight ahead of me and water surged up the steep beach around me. As it flooded back out to sea, the force knocked me off my feet and I was dragged straight out in what I had read about but never seen or experienced – a rip pulse.
Rip pulses are generated by high-energy waves suddenly appearing after a calm period, with the result of a rapid acceleration in the current from 0.5m/s to 2.5m/s in just a few moments. It was fascinating to be in one, but intimidating too - and it made me realise how easy it can be to suddenly panic. But this is the worst thing to do. Instead, lie back [it makes you more buoyant], breathe deeply [it helps you float and stay calm] and raise you arm with fist clenched. The lifeguard on the beach will be looking out for just this signal and you’ll be rescued in no time. If it’s their day off and you’re on your own, the strategy is simple: swim across the current and in with the waves.
Above: Surveying the beach from high ground helps spot rips
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