The treacherous North Sea – about undertow and rip currents

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You will take care of the things you know – is a saying used among nature interpreters. What is meant is that we should be considerate to nature by not being litterlouts or vandals. But by the North Sea the saying could be turned into “How can we take care of ourselves in the nature?” Unfortunately, there are drowning accidents along the coast of the North Sea every year, and some of these accidents might be avoided if we gain knowledge of the currents along the coast. In this article you can read about two ‘dangerous’ coastal currents – the undertow and the rip currents.

Undertow – Water that prefers to be level!
This will not come as a surprise to you but it is what you must have in mind if you want to understand how both undertow and rip currents develop. When it blows against the coast the water will be pressed towards the beach –it is said to pile up. The stronger the wind the higher the water is pressed towards the beach – but gravity is working against it. Water will always find the easiest way out, and it returns seawards again along the bottom and thus creates the phenomenon known as undertow. Undertows develop on steep coasts where there is room for a backwash. It will not develop on flatter coasts because the wind will influence part of the column of water. Then water will be pressed further and further landwards and in that way flood relatively large areas.

Rip currents
Rip currents are found only on coastlines with sand bars. The sand bars are sand banks parallel to the coastline. Think of them as a kind of wall that the water has to pass over to get on to the beach. When the wind is onshore, more and more water will be pressed behind the sandbars, and it has to go seawards again (as with the undertow). There will always be a weaker point in the sandbar where the water can ‘dig’ through, - thus creating a hole – a rip current! The rip current can be compared to a fast-moving conveyor belt travelling offshore, and if you are caught in it, you can be swept out to sea. If you have never heard about rip currents you will most likely fight it as best you can, but it is an unfair match – most often ending with a drowning accident. In stead, let yourself float out, and swim along the shore away from the rip current. Then you will be able to reach the beach again. There is another possible danger connected to rip currents. The currents around the rip current, between the sandbars and the beach, are travelling towards the rip current, so you may risk being pulled into it if the current is strong enough.

How to Identify Rip Currents
Rip currents are dynamic and you cannot count upon them being in the same spot every day, but some beaches are more prone to rip currents than others. It could be a good idea to talk to the local people or a beach lifeguard to find out if there are rip currents. If this is not an option and the water is too tempting you may be able to spot the rip currents from the beach. See if there is a place where there is a break in the wave line across the sandbar – the rip current is deeper than the sandbar, so the wave will not break. Another good sign is an area having notable difference in colouring. There is a strong current in the rip current which means, that the water is able to transport lots of sand and even stones which colour the water.

Safety tip
Always swim on beaches with the blue flag of approval, preferably at a lifeguard-protected beach.

If you want to know more
On the following websites you can read more about safe swimming:
* Tryg på Stranden:
* Kystlivredderne:
* Rådet for større badesikkerhed:
* Or you can visit the Kystcenter in Thyborøn and learn more about undertow, rip currents and the dynamics of the coast

By: Nature interpreter and coast morphologist Ulrik Geldermann Lützen, Kystcentret, Thyborøn