Waves on a slope

Earlier this year at Forscherfreizeit Ratzeburg – the summer camp at which Conny, Siska, Martin, a bunch of teenagers and myself spent a week sailing, exploring and playing with water – I spent a good amount of time staring at waves hitting the wooden boards that form the slip in the port. They create a nice slope with a very interesting structure, especially at the joints where the angle of the slope isn’t exactly the same.

Watch what happens when the wave approaches the shore (and focus on the left part of the picture, where it is clearer):

At first, it arrives pretty much as an ordinary wave.

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As it is running up the slip, you start seeing the structure of the boards below.

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As the wave becomes steeper and steeper, the front one is being slowed down more than the second one, because it is in shallower water (and we all know that the phase velocity of shallow water waves depends on the water depth, right?).Screen shot 2015-09-26 at 4.41.34 PM

Eventually, they form one steep wave and break.
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Watch the movie to see it happen:

For more waves on a slope, check out these posts (Norway, Hawaii).

Types of breaking waves depending on steepness of slope – small scale

Video of different types of breakers – small scale.

In this recent post we talked about types of breakers depending on the steepness of the slope. But even on a single stretch of coast line you can easily observe several kinds of breakers. My friend E lend her cabin on an island just outside of Bergen to me and another friend E for the weekend, and just sitting on the rocks we could observe at least two types of breakers.

Different types of “breakers” depending on the slope of the beach. Also see video below where it might become more clear…

In the movie below, you see surging breakers on the first little headland – the water level just raises and falls and no breaking occurs – whereas in the small bay behind the headland and on the next headland the slope is much less steep and here spilling breakers develop. Spilling breakers can also be seen about halfway through the movie on the right hand side beach. Isn’t it awesome how you can see so many concepts on the smallest scales once you start looking for them?

Waves breaking depending on steepness of the slope

Waves breaking on slopes of different steepnesses.

Depending on a slope’s steepness, waves can break in very different ways. On nearly horizontal beaches, spilling breakers develop. On steeper beaches, plunging breakers, the kind of breakers that form the tunnels that people surf in, form. And on very steep beaches, the breakers don’t actually break, but surge up and down.

Types of breakers developing on beaches depending on the beach’s slope.

This can be seen on  the large scale when different beaches are known for different kinds of breakers, and one impressive example are Oahu’s North Shore plunging breakers that my friend Tobi took me and a couple of friends to see in 2010.

Plunging breakers on Oahu’s North Shore in September 2010.

 

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Another plunging breaker on Oahu’s North Shore. See surfer for scale.

More awesome breakers were to be seen on the Big Island a couple of days later:

Plunging breakers on Big Island in September 2010.

And of course I have movies of those breakers for you, too, first Oahu and then Big Island: