Tracking Shifting Sands Along the Nation's Coast
Friday, July 12, 2013
As New Yorkers braced themselves for Hurricane Sandy, coastal geologist Cheryl Hapke was out surveying Fire Island, a barrier island off the Long Island coast. Days later, Hapke was back to document the hurricane's effects and found a breach cutting the island in two. Now locals and scientists are debating whether the inlet should be filled in or left as nature intended.
IRA FLATOW, HOST:
This is SCIENCE FRIDAY. I'm Ira Flatow. When Hurricane Sandy roared through the Northeast last fall, many of us where battening down the hatches, buying extra food and water, preparing for hours and maybe even days for loss of power. But my next guest actually flew up here from Florida to meet the hurricane. Hurricane Sandy presented an ideal opportunity for scientists to study how a powerful storm can reshape the coastline, and in this case, the coastline of Fire Island, a barrier island just off of Long Island.
And Sandy did indeed leave her mark on Fire Island. Sandy cut a channel right through it, exposing the bay above the island to the ocean. What can we learn from that? Should we fill in the channel? Should we rebuild barrier islands and sand dunes and sand bars, as we have before? Or should we just leave them alone, as nature intended? Let's see what happens.
Cheryl Hapke is coastal geologist at the U.S. Geological Survey in St. Petersburg, Florida. Welcome to SCIENCE FRIDAY, Dr. Hapke.
CHERYL HAPKE: Hi, Ira. Thanks for having me.
FLATOW: You're welcome. So you were right out there, right before Sandy hit.
HAPKE: Yes, that's right. We had been studying Fire Island for a number of years, looking at issues of coastal erosion. And Sandy, when we really saw that the path that it was projected to take, we realized this was probably a once-in-a-career opportunity to get a picture of what the beach looked like just before a storm of this magnitude hit.
So we flew up and did some surveys of the beach two days before Hurricane Sandy hit, at the same time that they were evacuating the island.
FLATOW: And so what did Sandy do to the island?
HAPKE: Well, from a scientific perspective, it was pretty amazing. What Sandy did to the island is what we as scientists would have expected to happen, but when you actually see it on the ground, it's truly amazing. The beaches were severely eroded to levels that we had not seen or measured before. The dunes had over-washed, or were completely destroyed along 50 percent of the island. And then the tragedy of the loss of many, many homes and other infrastructure on the island.
FLATOW: And it cut that channel right through the island.
HAPKE: The island actually breached in three different places during the storm. One was a very small breach, which closed on its own just rather quickly, within several days after the storm. One was closed mechanically, sort of following the traditional methods that we use. And one is still open today.
FLATOW: Do the neighbors there want the breach closed?
HAPKE: Well, you know, it goes both ways, Ira. The breach itself is in a federal wilderness area, so there are no homes immediately adjacent or even really nearby to the breach itself. However, across Great South Bay is the densely populated and heavily developed coast of the south shore of the mainland portion of Long Island. And the concern is that if the breach remains open, then in future storms, it puts those communities at greater risk of flooding in the event of the next storm.
FLATOW: I had heard people saying that the breach actually cleaned out the bay. Fresh seawater came in, and the bay being a bay where people are all living, it short of cleaned it out. Did you see any of that?
HAPKE: Well, you know, I don't - I'm not involved personally in any water quality assessments or measurements. We did hear anecdotally that the bay was cleaned out. One thing we know for certain is just natural breach processes - well, breaches are part of the natural process of a barrier island system. So they are expected to happen to maintain both water circulation in bays, to deliver sediment into back-bay areas, which can provide increased habitat and provides, you know, sediment and moving the whole island landward.
FLATOW: So if you left it alone, Fire Island as it is, and let the - nature take its course, what would you expect to happen?
HAPKE: From our studies in the past and from what we know about the behavior of this particular barrier island, it's pretty certain that this breach will close on its own. The big question on the table, though, is how long will it take to do that. We would have expected a small breach like this to close up, but those series of very powerful nor'easters that occurred throughout the winter after Sandy really left the system more vulnerable and exposed. So the breach remained open longer than we expected. And, you know, there's a good chance that it may close on its own sometime before the end of the summer, if we don't get another big storm.
FLATOW: And so what do you want to learn about what happens to the sand there?
FLATOW: Along all of Fire Island, when a storm comes through, or its natural movements.
HAPKE: Yeah. When large storms occur along barrier island systems, that is the process by which sand is actually moved landward. And in the long term, that is how barrier islands keep up with sea level rise. So it's actually a very important process of the - part of the natural process of the system for sand to be picked up during storms and moved into the center part of the island or into the back bay.
And one of the most rapid ways to do that effectively and efficiently is through island breaching.
FLATOW: So the hurricane naturally is moving the island northward itself?
HAPKE: Yes, that is the process of how barrier islands move through storms like Sandy.
FLATOW: Uh-huh. And this would happen over a period of hundreds or years, tens or years?
HAPKE: Hundreds of years, thousands of years. The barrier islands along the East Coast of the U.S. have been migrating toward the mainland coast for a number of years, for thousands of years.
FLATOW: And so when people put their beach homes up along the sand there, are they effectively blocking what the ocean wants to do and move that sand northward?
HAPKE: Yeah, that's absolutely correct. For a natural barrier island to keep up with sea level rise, it will move landward in response to sea level rise and storms. By building and holding those barrier islands in place, we're not allowing them to move. So the only thing that we can do is build them higher and higher. So as we want to maintain barrier islands in the same place, where it's going to require more and more sand to re-nourish them to do so.
FLATOW: And, of course, if the ocean is rising, you have this tug of war going on, then?
HAPKE: Oh, that's exactly correct. So - and that's why we will need increased amounts of sand into the future to be able to maintain them in place.
FLATOW: And where do you get the sand from?
HAPKE: Most of the sand right now comes from deposits on the intercontinental shelf offshore of, in this case, Fire Island, but all up and down the East Coast.
FLATOW: And do we know if there's enough sand out there for...
HAPKE: You know, that's a figure we don't know. There's certainly enough sand for short term. By that I mean 50 years, maybe 100 years. But who gets the sand is going to become a question that we'll have to answer. And another question is, at some point, the economics of mining that sand and placing it on the beach maybe just outweigh - the cost may just outweigh the number of homes that it's saving.
FLATOW: So what do you want to study? What do you want to know? What are you going to be looking for?
HAPKE: I think that the number one thing that we're looking at and studying the breach and studying the beaches and dunes of Fire Island is to try to understand where they are most vulnerable and where they are most likely to breach or over-wash in future storms. And this can be used by coastal managers and planners as they try to move forward with managing the land.
FLATOW: Fascinating. You're hoping for another storm somewhere, to go storm-chasing?
HAPKE: You know, I'd like a couple years to work up the data from Hurricane Sandy, to be honest. But, you know, if another storm occurs, we'll be there.
FLATOW: Yeah. They've predicted hurricanes for this season. So...
HAPKE: They absolutely have, yes.
FLATOW: Thank you very much, Dr. Hapke.
HAPKE: You're welcome. Thanks for having me.
FLATOW: You're welcome. Cheryl Hapke is coast geologists at the U.S. Geological Survey in St. Petersburg, Florida. Transcript provided by NPR, Copyright NPR.View this story on npr.org