![]() When water hits the wall and is deflected around it, this leaves an area of low pressure immediately downstream of the obstruction. These are eddies, created from pressure differences either side of the obstruction. However, if you add an obstruction like a jetty, harbour wall or headland, it will create counter-currents that flow the opposite way. On an open coast, tidal currents flow from the surface to the seabed and all the way out to sea, like a great river. ![]() Beware of eddies in enclosed bathing areas Either way, we battled our way to the pier and raced back at an Olympian 6 knots 3 knots of propulsion on top of a 3 knot current. In the end, I got out and walked up the beach to Danny’s credit he stuck it out and ‘beat the bend’, a feat partly motivated by his disinclination for walking barefoot on pebbles. On the single bend of the swim, the torrent was so strong that we spent five minutes opposite the same yellow house on the seafront, despite our trick of staying close inshore where the flow is weakest. On a recent session with my swim buddy Danny Burrows, we challenged ourselves to a 500-metre slog against the currents to Deal Pier. Where I live in Kent, the northerly currents at high tide allow me to swim three miles up the coast from Kingsdown to Deal without any trouble at all it would be impossible against the southerly stream at low tide. ‘In the end, I got out and walked up the beach’ This cycle has a monumental effect on how far and fast we can swim. On tidal rivers and estuaries, Slack Water is closer to high and low tides with currents flowing inland as the tide rises and back out to sea as it falls.Īfter Slack Water, currents speed up for three hours then slow down for three hours, changing direction at the next Slack Water. ![]() The exact time of ‘Slack’ is unique to every beach, but on an open coast it is generally around 2 hours before high tide and 4 hours after high tide. The effect on your local beach is that currents flow along the shore for six hours at a time, changing direction at set hours before and after high tide – a time known as Slack Water, because the currents are literally slack. Then, when the peak arrives six hours later, it ‘pushes’ the currents along with it east up the south coast, south down the east coast and north up the west coast. Using an analogy of a tidal wave, I explained how at low tide currents are ‘sucked’ towards the peak, hundreds of miles down the coast. In my last article, How Tides Work, we explored how tides are made by giant waves flowing along the coast, with high tide at the peaks and low tide at the troughs. ![]()
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