A bit of scribbling just cropped up in New Scientist. Here’s the first 200 words or so:
It’s about some neat research into the way rip currents work – great food for thought during those endless counterproductive paddleouts at your local beachbreak.
It was interesting to write for a straight-ahead magazine like New Scientist. Forget these fanciful Scribble posts, where I get to mosey around in whatever I think is interesting; this story was concerned with explaining What Happened. And I didn’t even get to do all of that in my 1,200 words. Here are some things that had to get left out:
By the way, the above picture of rip currents is all wrong. Here’s something a little closer to reality, according to drifters deployed by Jamie MacMahan and colleagues (thanks, Jamie). White arrows indicate current speed and direction:
The term “rip current” wasn’t even invented until about 1925, in Science, when some scientists rebelled at the notion of the “undertow myth,” kicking off a flurry of indignant correspondence.
Francis Shepard, of Scripps, pioneered rip current research – taking measurements while dodging set waves in a rowboat.
In the 1960s, other researchers tossed waterlogged whiffleball-like floats into the surf. They tracked where they went using a camera dangling from a helium balloon.
Until this year, even the most intensive rip current studies recorded very few measurements in rip channels themselves. It’s just too dang hard to install a current sensor with a freakin’ rip current whipping past you at 4 knots.
Jamie MacMahan, one of the scientists I wrote about, said six years ago they did manage to install a sensor in a rip channel north of Monterey. It ran on batteries and logged data to a chip to be recovered after 3 weeks or so. They’ve never found it. “As far as we know, it’s still down there, it’s just a lot deeper,” he told me.
MacMahan is cool. Young, already an assistant professor at the Naval Postgraduate School. He’s a little shorter than me, fit but rounded, kind of like a polar bear. Most of the time I talked to him, he had salt water running down his nose. When he’s in the office, he kicks his flip-flops off next to his hard drive. He figured out how to use off-the-shelf GPS for his surf drifters by cruising techie blogs. He invented a way to measure sea floor contours in pounding surf using a depth meter and a jet ski.
The GPS surf drifter was invented by Wilford Schmidt when he was a Ph.D. student at Scripps. He’s now a professor at U. of Puerto Rico in Mayaguez, where he surfs choice Caribbean waves early in the morning. He’s starting to study wave turbulence by installing video cameras in the crystal clear tropical water. He says, kind of gloatingly, that the only reason no one’s done it before is that at the world’s major oceanographic research centers, the water’s just too murky.
Tim Stanton, the other Naval Postgraduate School researcher in the story, studies the other side of rip currents. Where MacMahan’s interested in how the sand shapes the water currents, Stanton’s interested in how the water moves the sand around.
Here’s a classic example of the trials of field research: Stanton’s focus for this year’s field experiment was deploying a super-high precision instrument that measures how much sand is moving in the current, in 1-centimeter slices through the water. He designed the electronics himself and built the instrument to measure continuously for several weeks.
How’d it work? Well, one drawback to studying rip currents is you have to put your instruments in rip currents. The very first day, some kelp got caught up in a rip, recirculated in the eddying flow, and knocked the instrument flat. Last time I saw Stanton, he was planning an expedition for the next low tide to look for any remaining pieces of the instrument.
In the New Scientist article, Ad Reniers is a Dutch modeler who’s a whiz at fluid dynamics. In person, he wore a flaming orange Hawaiian shirt. It was unbuttoned far enough to see his Tecate temporary tattoo. (“Hey, Cinco de Mayo, man.”)
I had an interesting chat with Dr. Edie Gallagher, who studies sand transport at Franklin and Marshall College in Lancaster, Pennsylvania. Standing there in a wetsuit, still dripping wet, she looked at the undulating beach in front of us and said something like, “It’s basically an exact reflection of the waves that strike this beach. The sand that’s here is here because these waves leave it. Anything finer, they carry out. Anything coarser stays up in the rivers.” That, to me, was a whole new way of looking at beaches.
Thanks to all the scientists who helped me write the story.