STRUCTURES

In this extract from Coast Magazine [June 2019] William uncovers what you can learn by looking at coastal structures.

My favourite structure is the pier. I am on one now, 312 metres off the British coast. A new café, Deal Pier Kitchen, has recently opened in the architecturally acclaimed timber and glass pavilion at the end of this brutalist concrete structure, and it’s in there that I’m writing this feature. Waves are surging beneath my feet, clouds swirl past the windows, and here I sit with my latte, pen and paper - simultaneously immersed in nature and shielded from it. But what really draws me to piers is that they take you away from the land and life’s little problems, without having to squeeze into a wetsuit or pump up a paddleboard. In just 312 windswept paces I can step back and dream big. 

 

Piers are practical too. Whenever I drive past Deal Pier I quickly glance at the legs to check the tide. The high water mark is clearly defined by the transition from dark barnacled growth below to the smoother, lighter concrete above. By observing how much dark leg is exposed I can work out the approximate tide height; it can range by 6 metres, or the height of a two-storey building. The three tiers provide a reference point too. Through the engineers’ miscalculation the lowest tier is underwater 30% of the time; when the tide is 4 metres the level becomes flooded. It takes a 7-metre tide to cover the middle tier; on the rare occasions this happens the sea is dangerously high and the town is at risk of flooding, so batten down the hatches!

 

Above: William’s son Arva inquisitive about a shell, safe from the High Tide - shown by the seaweed on the concrete.

The pier also tells me which way the currents are flowing. When water hits an obstruction like pier legs it is compressed and flows past at accelerated speeds. This leaves an area of low pressure immediately downstream of the structure and nature maintains equilibrium by creating a counter-current pushing water upstream to ‘fill the gap’. Where this slow-moving eddy meets the fast-flowing current, the two streams collide and create turbulence. This is called an eddyline. Sometimes they look like shadows running from the base of the obstruction, but often the sun is in the wrong position and you can be confident it’s a clue to the currents.

THE EDDY

 

In extreme cases eddylines can create whirlpools capable of sucking a swimmer down to the seabed; the biggest maelstroms in the world grow to 10 metres in diameter and extend 100 metres beneath the surface. So stay away from big rocks or bridge legs in areas of strong currents! Fascinatingly, tidal whirlpools can be observed in central London. Although the capital is 50 miles from the coast, a rising tide at sea creates a huge 7-metre range at Tower Bridge with strong currents flowing upstream against the rivers’ natural gravitational flow. When these currents collide with the bridge legs you can clearly see the eddylines; once a month I lead a Tide Walk along the river and we stop by the Blackfriars Bridge to marvel at this mesmerising phenomenon around its legs. 

 

On a larger, but gentler scale, the eddy concept happens where coastal structures are built at right angles to the prevailing tidal currents. Brighton pier is a perfect example. Although it is not a solid structure, there are so many legs that it has the effect of a ‘wall’ with tidal currents deflected to the end of the pier, where streams are accelerated. Just downstream of the pier an eddy forms. Swimmers and paddle boarders on my Tide Walks have noticed that the currents are often different on either side of the pier - this is why. So if your Tidal Compass or Imray Tides Planner App is saying the currents are flowing one way, but they are actually taking you the other, look around for coastal structures [or the natural geography of the coast] because chances are you’re in an eddy.

Above: Structures create Eddy's with counter-currents

 

TIDAL POOLS

When I am in Deal I try to swim in the sea every day at 12:00. This gives me something to get excited about throughout the morning and re-invigorates me for the afternoon. A series of posts running along the beach prove invaluable to the success of these swims - each for its own reason. One is where my swim buddy Danny leaves his flip-flops so they can be easily found after [no simple feat on a long pebble beach]. Another is home to a semi-resident Cormorant who faces into the wind to dry his wings – our natural wind vane. The most useful structure has a rope dangling from it, pulled away from the post by the current and pointing us in the direction we should swim if we want to go with the flow, or challenging us to go the other way if we want to test our stamina by swimming into the stream. Finally, there’s the destination post that we set our sights on, not stopping until we get there, then clinging to it with all our strength as the currents race past like a raging river in full flood. 

 

One way to avoid this battle with the tidal currents is to head to your nearest tidal swimming pool. The design of these structures allows the flood tide to pour over the walls, which then hold the water in as the tide ebbs away. Our closest pool is in Walpole Bay, Margate, and it’s the largest in Britain, covering a huge 4-acre expanse. It was opened in 1937 so the local population could swim at low tide without having to trudge through mud over the slippery chalk reef. 

 

Above: Walpole Bay Tidal Pool in Margate

 

 

You can find tidal pools all around the coast and they are usually built where sea swimming is challenging – either because of the tide or the waves and rip currents. For this reason many are found in the wilder corners of the British Isles; Cornwall, northern Scotland, north-east England. With many built in the 1800’s and early 1900’s, their hard stone walls are softening around the edges, seamlessly blending into the coastline and becoming a natural part of the environment, perfectly positioned to give us safe sea swimming all year round. 

Please note: this is a shortened version of the main feature. To enjoy the full features each month, you can subscribe to Coast Magazine here.

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Write to: Tidal Compass Limited, Coast House, 32 The Beach, Deal, Kent, UK, CT14 7HN

 

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