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In the second instalment of our Sea Signs series William explains what makes high tide and explores the depths of knowledge you can uncover by simply observing the time it happens.


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Tide is made by giant tide waves flowing along our shores; when a peak passes we experience high tide and six hours later the trough brings low tide. There are three main tide waves flowing around Britain; one on the west coast, one on the east coast and another on the south coast. The peak of each wave always travels in the same direction; on the south coast it travels from Lands End towards Dover and on the east coast it travels south from the northern tip of Scotland. Fascinatingly, the peaks of the southern and eastern waves converge off Thanet at exactly the same time, join together, cross the channel and travel up the European coast towards Norway. The peak then returns to the northern tip of Scotland and repeats the same cycle, over and over again for thousands of years. 


Although tide waves and surfing waves are made by completely different forces, the two have a fascinating interaction when they meet at a beach - especially if the gradient of seabed changes with the tide. On beaches with a shallow gradient, waves break slowly with a shallow face; ideal for beginners and longboarders. On beaches with a steep gradient, waves break fast with steep faces; ideal for professionals and shortboarders. This is where tide comes into the mix; on beaches like Croyde in North Devon at high tide the waves interact with a shallow-sloped seabed, but at low tide they interact with a steep-sloped seabed. So although the swell can be exactly the same throughout the day, experienced shortboarders are better timing their surfs for low tide while beginners should go out at high tide. 


The arrows show the direction Britain's tide waves travel, with each line indicating an hour's passage of a peak

I use the Imray Tides Planner App to check the tide; it gives you the tide height every five minutes simply by running your finger along a graph on the screen. If you prefer old school methods a local Tide Table will give you high and low times and heights for every day of the year. Failing that you can always look to nature; in last month’s Sea Signs feature I explored how you can work out the tide by simply observing the moon. You can also get a good idea of what’s happening by looking for signs on the beach.


The main reason why it’s important to know the time of high tide is so you don’t get caught out by the rising tide, appropriately named the flood. On expansive flat beaches like Morecambe Bay it really does feel like a flood; they even have a siren that alerts you of its arrival. When the siren goes, get back to shore because the tide is said to race in faster than a galloping horse. Whether or not this is true, on shallow-gradient beaches a small rise in the tide floods a large area of beach very quickly and you don’t want to be caught out – especially with quicksand around! This is why it’s sensible to head out when the tide is falling because it gives you more time to safely enjoy the beach before the flood gallops in.


While the flood tide comes in on flat beaches, it has a more dramatic effect going up on steep beaches – especially where there are cliffs. I used to volunteer with the Walmer Lifeboat in Kent and every year we would get ‘shouts’ to rescue people stranded beneath the White Cliffs of Dover. The reason this happens so often is because people think they’re safe on a higher stretch of beach, unbeknown that around the corner the rising tide is flooding a lower stretch of beach and cutting off their means of escape. If you have a regular walk under cliffs a simple way to avoid this happening is to note the time when the lowest section of your walk gets flooded; on your Imray Tides Planner you can find the height of tide when this happens. Note it down and plan your outings for when the tide is well below this level, allowing for the effects that weather can have on the tide [we’ll explore this in a feature later in the year].

Cut-off Cove. Just one more reason why you should observe High Tide.

Knowing the time of high tide will keep your feet dry, but if you prefer total immersion it’s important to know the tide time because this will tell you which way [and how fast] tidal streams are flowing along the coast. Every beach has its unique cycle of tidal streams but the general pattern is that currents flow both ways along a coast, changing direction every six hours at set times before and after high tide. The time streams change direction is called Slack Water and it’s they’re weakest in either direction; after slack they speed up for three hours then slow down for three hours until the next Slack Water, repeating the cycle in the opposite direction. 

“the time streams change direction is called Slack Water; this is when they are weakest in either direction”

Tidal streams are generated by the tide waves flowing along our shores. The best way to understand how they work is to imagine you’re swimming in a surf beach. You’re facing out to sea and as a wave approaches it sucks you towards it. When it arrives the wave then surges you back towards the beach. This is exactly the same principle of how tide waves create tidal currents, albeit on a much larger scale. It also explains a useful piece of knowledge; at high tide currents are always flowing in the same direction as the peak of the wave. So if you know which way the tide wave travels around a sea or ocean, you can predict the direction of streams when you travel somewhere new simply by observing if it is high or low water. 

Knowing the direction and speed of currents every hour before and after high tide means you can plan your adventures for when the conditions are best suited for your activity. If you’re swimming with kids the safest time is Slack Water as it’s easiest to stay in one place without getting swept along the beach and separated. If you’re kayaking or paddle-boarding you want to time your trip for when the currents are going the same way as you. I’ve seen people paddle without getting anywhere because they unwittingly went in when the currents were at their maximum speed of 3 knots [5.55kmh] in the opposite direction.


When Naomi and I met we spent much of our first summer drifting back and forth along the coast on a battered old windsurf board we traded with a local fisherman for a lobster pot I found on the beach. Naomi would dangle off the back of the board with the fishing rod and I would paddle and navigate. I always timed our trips for a couple of hours before slack water so the currents took us along the coast and then back to where we started, a several mile trip without me having to paddle at all! This can be done anywhere in the world where there are tidal streams, and it makes adventures infinitely more fun, fast and satisfying. 

In the next Sea Signs feature William will uncover the huge amount of information you can gather by simply looking at the boats around you.

About this series

Every day the sea is different, a  result of the ever-changing interaction between the moon, sun, tides, wind, waves,  buoys, boats and the beach. While the picture may appear complex, like a piece of classical music, it is essentially just an arrangement of simple elements, or notes. By dismantling the machine into its component parts and exploring each one in detail we can create order out of chaos; clarity out of confusion. That is the  purpose of this series 'Sea Signs'.

When we are young we learn to navigate urban environments; what traffic lights  mean or how to cross a road. What many of us aren’t taught is how to read nature’s  signposts; how to judge wind by watching birds or what weather different clouds  bring. Then there’s a whole technical world of buoys and boats with different light  sequences, colours and signals communicating messages. My goal in this series is to  share with you all the signs – both natural and man-made - that you may encounter in  your adventures along the coast so you can read them as well as any yachtmaster  skipper or crusty old seadog. 

With this knowledge, nothing is going to slip under your radar.

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