Beach Recovery

(Video: Tuba Ozkan-Haller)

(Tuba Ozkan-Haller): "What we're trying to do here is figure out how beaches recover after very many storms, after being subjected to a lot of storm waves during the winter months.

"My name is Tuba Ozkan-Haller and I'm an assistant professor in the College of Oceanic Atmospheric Sciences here at Oregon State University.

"People who have lived near the coast know that in the summertime the dry beach actually increases. There's more sand that is just sitting on the dry beach area in the summertime. And that sand actually goes away in the wintertime because of the storms and forms a bar, sort of a submerged island offshore. It's the way that the beach protects itself."

(Video: animation of beach recovery)

(Tuba Ozkan-Haller): "As the summer then approaches again during springtime, waves move that bar, that mound, back onto the beach. And, we found out that we're actually very bad at predicting how that happens or figuring out exactly what about the waves makes that sand move back onto the beach.

"So this experiment was designed to observe an event where the beach is recovering after storm conditions. And we basically have a big advantage in the lab where we can observe this happening under controlled conditions and really measure everything about it, so we can figure out exactly what property of the waves takes the sediment and moves it back onto the beach.

"Once we do that, that knowledge is basically incorporated into already existing beach erosion models so that now those models can also predict how beach accretion happens. Now, why could that be important or why would the…would a person have interest in this? Oftentimes, there are periods, years, where the storm activities increase."

(Video: animation showing warming of equatorial and coastal waters)

(Tuba Ozkan-Haller) "This happens a lot during El Nino years, for instance. So, after an El Nino year has passed and there's been a lot of storm activity, a lot of erosion has happened, some infrastructure or property may be at risk.

"And then the decision needs to be made as to whether or not to protect that property – a bridge, a road, for instance, or any kind of private property – or whether or not in the coming spring months the beach is going to recover enough to form a natural barrier again.

(Video: property damage from severe storm weather, recent construction on the edge of a beach bluff)

"So for that kind of prediction, we need tools that can figure out exactly how much or how that sediment is coming back onto the shore, so we can figure out how in the spring whether or not the beach will provide enough natural protection.

"So, eventually what we see happening to this research is we figure out the particular hypotheses that's responsible and then that gets trickled down. It actually gets incorporated into models that predict beach behavior in the summer and winter months, so that we now have a tool that will help us make decisions about whether or not to protect a particular structure.

"Our approach to solving this problem is to take the problem into the lab. And, in general, labs have advantages over doing things in the field, because you have control over the particular event that you're studying. You have control over what kind of waves you're generating and you have control over stopping the waves if you want to, in order to look at what happened to your beach."

(Video: wave generator working and waves in flume)

(Tuba Ozkan-Haller): "We're actually studying what we're doing in a very large tank; almost full size, really. It's over a hundred meters long, about four meters wide and about five meters deep, and we can generate waves that are anywhere from three seconds to nine seconds in length. And these are very realistic ocean waves, so we don't have to have any of the issues of scaling down our experiment. We can actually look at it in full scale, so this gives us the ability to transfer the knowledge that we've gained here directly to the ocean."

(Video: comparison of beach in wave flume to a natural beach)

(Tuba Ozkan-Haller): "We use a platform to measure slices of the wave tank. Basically, figure out what's going on at a particular location. This platform is actually moveable. It's on wheels, so we can move it up and down the tank. And at one point, when I was talking to the graduate students about it, I mentioned to them that there was maybe two hundred thousand dollars worth of instruments on this cart and that that's really the equivalent of my house."

(Merrick Haller): "Optical backscatter instruments, Acoustic Doppler Velocimeter. Multiple transducer array. Three video cameras that are mounted up near the ceiling. Wave gages – and these are actually mounted on the sidewall of the tank.

"I'm Merrick Haller and I'm on the faculty in Civil Engineering. We have about eight or ten optical backscatter instruments. This is an example of one. And it emits light from this end here and then measures the amount of that light that is scattered back towards the instrument due to sediment particles in the water column.

Not only do we want to measure how much sediment is suspended in the water column, but which direction is it going. And with those two quantities, we can calculate how the beach will change at this location.

And how we measure the…the flow velocity is with an acoustic instrument. This is called an Acoustic Doppler Velocimeter. And the way it works is it sends out acoustic pulses from these four probes, and that pulse is scattered backwards from any small particles within the water column. And those particles are moving with the velocity of the fluid, and so that acoustic pulse changes in frequency when it scatters backward from these particles. Just like when you hear a train coming past you at the railroad crossing, the frequency of that sound changes as the train approaches and then moves away from you. And the amount that frequency is changed is related to how fast and what direction the train is moving, or the fluid is moving in our case.

We also are taking remote sensing measurements in these experiments, and what we have is a sequence of three video cameras that are mounted up near the ceiling. And what those do is track when and where the waves start breaking. So when a wave breaks, the bubbles and foam that is generated shows up very cleanly in video imagery. And so we can use that as another comparison between our numerical models and between our observations – do the models predict where and when the waves break, and we compare that to the video data."

(Tuba Ozkan-Haller:) "Our team is made up of a number of people. We've got faulty working with us, we've got graduate students,..."

(Video: student talking on a walkie-talkie)

(Tuba Ozkan-Haller:) "... we've got technicians working with us. And everyone fills sort of a different roll. The entire team has to basically take care of their parts and do it just at the right time so that the workflow isn't interrupted.

"In the beginning, doing this was quite a challenge."

(Video: two students lifting a frame on the mobile cart)

(Tuba Ozkan-Haller:) "It took us awhile to figure out exactly the timing that … with which everything needed to happen. Towards the end, at the end of the four weeks we'd become pros. We were actually doing everything with such efficiency that we were getting in something like fourteen or fifteen runs a day."

(Video: time-lapse of people working on cart)

(Tuba Ozkan-Haller:) " But doing that, of course, means that you're constantly on for the whole day. You're paying attention to exactly what everyone else is doing and what order they're doing things. At the end of the day you're completely exhausted. It's a…It's a very, very tiring process, but we got a good data set for it.

"We've got a lot of measurements of what went on in this particular tank during a four week period. And now we're on to the laborious task of figuring out exactly what all those numbers are telling us. Trying to see which of the hypotheses are the ones that really win out. And we've already gone on to that task and each of the graduate students has picked up some of the hypotheses and is going on to try to figure out if the data supports that particular hypothesis.

"Once all that is done, we'll basically be ready to operationalize this; put it into these predictive tools with which we can figure out what's going to happen to the beach next year or after the next severe storm season, so we can figure out whether or not things need protection or how to do beach nourishment, and things of that sort."

[End of Interview.]