Wetlands and Flooding in New Orleans Historically, wetland vegetation works as a buffer zone during hurricanes. Now that so much is gone, New Orleans is at greater risk of flooding. Experts say the change is due to the building of levies along the Mississippi river delta to protect New Orleans from floodingMelissa Block talks with oceanographer Joe Suhayda, who studies coastal wetlands in Louisiana.
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Wetlands and Flooding in New Orleans

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Wetlands and Flooding in New Orleans

Wetlands and Flooding in New Orleans

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MELISSA BLOCK, host:

The levees built to protect New Orleans have also kept the Mississippi River from flooding as it naturally would. Without the silt deposits from flooding, the wetlands and barrier islands that would act as a hurricane buffer have been disappearing. So when a hurricane blows through now, its effect is magnified. Joe Suhayda is a coastal oceanographer who studied how quickly Louisiana's coastal wetlands are vanishing.

Dr. JOE SUHAYDA (Costal Oceanographer): The rate is really the most extreme in the United States. But in terms of absolute numbers, we're talking about--over the last couples of decades, it was as much as 40 square miles a year. Now we're talking about something--because I think there's less wetland to lose, we're down to around 20 square miles a year.

BLOCK: And what's the effect of that erosion, or disappearance of these wetlands, when you have a hurricane come through like this one?

Dr. SUHAYDA: Well, those wetlands were located between, really, where the development exists and the Gulf of Mexico. So it was like an apron between the higher ground that was occupied, like New Orleans, and then the actual coastline. We had about 40 miles then of this very low-lying, intertidal, as it's called, marshy area.

BLOCK: And what function would that apron that you're describing serve during a hurricane like this?

Dr. SUHAYDA: The hurricane makes landfall and it's, of course, pushing the water landward. And that water, if it runs into some kind of resistance, like vegetation, is actually held back a little bit. So without having the vegetation there, the water has a more free shot to go right further north across what are now bays that used to be marsh, and so we end up now with a storm surge propagating more rapidly inland than it normally would have.

BLOCK: Mm-hmm.

Dr. SUHAYDA: The secondary effect is that given that the hurricane is fueled by warm water that it's passing over, if it were passing over a marsh area, that fueling process would be reduced somewhat. But with the wetlands gone--we actually have bays now where the wetlands used to be--the hurricane is still able to sustain itself a little longer than it normally would have. So actually, we have a little stronger hurricane and we have a situation where the loss of wetland has made it easier for the water to propagate inland.

BLOCK: Let's talk about some of the reasons behind this degradation of the wetlands. How have the levees that were designed to protect the city of New Orleans contributed to all of what you're describing right now?

Dr. SUHAYDA: What the levees accomplish is it prevents water, of course, from getting out of the normal channel of the Mississippi River onto the adjacent land. That levee blocks that flow.

BLOCK: Blocks the flooding, in other words.

Dr. SUHAYDA: Blocks the flooding. But the flooding actually was transporting sediments and nutrients historically to those lands.

BLOCK: And all of that would have supported the coastal wetlands, would have supported vegetation there.

Dr. SUHAYDA: That's correct. Those plants depended on and, in fact, were built because of that process that occurred historically.

BLOCK: If you look at an overhead map of the coastline and compare what you see now with what you might have seen, say, 50, 60 years ago, how dramatic is that?

Dr. SUHAYDA: Oh, tremendous. I mean, we're talking about the shoreline that you would perceive as the edge of the marsh migrating 20 and 30 miles northward.

BLOCK: Twenty and 30 miles over how many years?

Dr. SUHAYDA: Since the beginning of the last century, maybe the 1930s.

BLOCK: Is there any money or any project under way to try to reverse this damage that we've been talking about?

Dr. SUHAYDA: Yes, there are. There is what is called the Breaux Act, which has been a program in effect for 15 years. And that has recently been added to by some additional monies from the federal government so that we'll have about another half a billion dollars to deal with the problem.

BLOCK: And how much will that be able to solve?

Dr. SUHAYDA: In terms of actual area, you're probably only going to be able to address maybe 10 or 15 percent of the problem.

BLOCK: Joe Suhayda, thanks very much.

Dr. SUHAYDA: OK. Well, thank you very much.

BLOCK: Coastal oceanographer Joe Suhayda, speaking with us from his home in Baton Rouge.

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