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Tuesday, February 25, 2014

Rip Currents for Surfers | Using the Rip to Paddle Outside

By Athair Baer
Hopefully, we’ve all had the life safety pep talk on how to avoid rip currents and why they're dangerous. This is true and appropriate measures should be taken in regards to rip currents. AND by appropriate measures I mean – c’mon! I’m telling you that there’s a current of water swiftly moving away from the shore! What do we do when we go out to surf? We’ve gotta paddle to get outside the break so we can pick n’ choose the best ride. Right?

Photo: Heidi Grabowith

What’s a rip current? Well, first, understand there are different kinds of rips, lots really. I’m aiming at the fundamentals. If you have a lifeguard warn you about a rip current and he adds in a funny word like “structural” or “longshore rip” you need to start asking questions for safety’s sake.

The best way I can explain the fundamentals of a rip current
is how they were originally explained to me: you’re in the bathtub, it’s full of water, someone pulls the plug, and the water starts rushing to the drain. That’s a rip current.

 What I’m talking about is pressure. Pressure’s the reason you hear that “pop!” Just before you hear the sound of the water draining in the tub.

Think about it: if the pressure in the drain was the same as the space the water occupies in the tub, the water would just stay put. Ever take a cup turned upside-down and pull it underwater? The water doesn’t rush into the cup because the air trapped inside the cup has a greater (or positive) pressure than the water in the tub.

Pressure at work in Pirates of the Caribbean

You see, there’s different levels of water at different places along the shore. When the waves crash and push up on the beach, they push around the sand, coral, and rock all up and down the coast. Some of it moves easily, some not-so-much. (Read: the Coriolis Effect). You also have to consider big waves versus small waves, storm swells and currents coming from different directions. All of it means more water in some places than others. More water means more pressure, and water always wants to go where there is less pressure.

diagram: the COMET Program

The above diagram depicts water levels along a shore. The “H” is where there’s a high amount of water, and the “L” – yeah, easy enough to see. Right?  Well, the “Low” is where you’ll find your rip currents. There’s no drain for the “Low” water to fall into right here. But since the water pressure to the sides of it are greater, it has no choice but to flow back out the way it came. On its way back out to sea, the “Low” water level is going to pull water from the “High” levels with it, all out to sea, and from the sides just as depicted. See the yellow arrows pointing to the “L” from the “H” levels?

What this means to you as a surfer: you’ve just discovered the highway to the outside, man! You see those sand-filled clouds of water that stretch way out and point away from the beach? You’ve found a means of paddling out that’ll take less energy and get you where you want to be a lot faster. If you have a big swell and tall sets to paddle through, you’ll appreciate that energy for safety’s sake. This is reason numero uno “why I love the rip.” 

see the rip?

Reason Number 2: Ok. Now, lets suppose the water levels on the shore are even, and you still have a rip. What’s the deal? This is caused by the same water pressure thing we just talked about, but the placement of the pressure inequality is different. Instead of the volumes of water being different along the shore, now it’s the shape of the sea floor that’s different. Those sandy bottoms have a current all their own. This is called the surge, and it paints all kinds of beautiful patterns in the sand. Teamed up with the waves and the tides, the surge creates sandbars. Literally, giant bars of sand that can stretch a few feet to hundreds of yards across or more! Think of giant speed bumps that parallel the beach. These create the famous “Undertow(!)” conditions and caution signs.

diagram: the COMET Program

These sandbars trap water and that water is added weight to the water above it. Every time a wave crashes above, that sandbar stretches with the sand being pushed around and the water wants out! Eventually, the water finds a weak spot in the sand bar and it breaks out, floods out, and runs a like an underwater river in a gutter to a storm drain. This is where you have your rip. 

What this means to you as a surfer and reason number two why I love the rip: that elongated splotch in the water that’s heading out to sea and is considerably darker than the rest (depending on your water) means it’s a rip, it’s deeper water, and you now have a better eye for where shallow points are – and where you don’t want to
eat it when you’re choosing whether or not you want to take a risk on a wave you’re iffy about catching. We don’t want you worrying about surfboard storage because you’re on hiatus for physical therapy after a spinal injury. Ya know?

Happy riding!