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Gulf Coast Rebuild to Include Levees, Wetlands

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Gulf Coast Rebuild to Include Levees, Wetlands

Environment

Gulf Coast Rebuild to Include Levees, Wetlands

Gulf Coast Rebuild to Include Levees, Wetlands

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After Hurricane Katrina, one of the greatest challenges is how to make New Orleans and the surrounding areas more resilient in the face of flooding and hurricanes. Melissa Block talks with coastal oceanographer Robert Twilley of Louisiana State University about how the wetlands should be rebuilt. They provide a buffer for storms but have been seriously eroded. Robert Siegel talks with engineer Hassan Mashriqui, also of LSU, about strengthening protections around New Orleans such as levees and canals. The city was flooded partly because of breaks in the levees and canal walls.

MELISSA BLOCK, host:

From NPR News, this is ALL THINGS CONSIDERED. I'm Melissa Block.

ROBERT SIEGEL, host:

And I'm Robert Siegel.

It will be a great task to make the city of New Orleans safe from hurricanes and floods in the future. President Bush stated the basic problem in his address last night.

(Soundbite of speech)

President GEORGE W. BUSH: Much of the city lies below sea level. The people who call it home need to have reassurance that their lives will be safer in the years to come. Protecting a city that sits lower than the water around it is not easy, but it can and has been done.

BLOCK: That means re-engineering the city of New Orleans, and it means restoring surrounding wetlands that create a buffer against hurricanes and floods. During a storm, those wetlands reduce the energy of the storm as it moves toward New Orleans.

Robert Twilley is a coastal oceanographer at Louisiana State University. He says in the last 100 years, about a third of the wetlands have been eaten up by the ocean. He tells his students that means an area of wetlands the size of a lecture hall disappears in the course of one lecture. Twilley explains it's because the area has become more and more developed.

Professor ROBERT TWILLEY (Louisiana State University): The coastal wetland landscape in Louisiana, you start with 1900, there was a 1927 flood, oil and gas explorations in 1940. Navigation really expanded in the--from 1920 to 1950. All three of those produced extreme changes and all kinds of artificial structures to our coastal landscape, and mainly it's all related to disconnecting the river from the wetlands. That disconnect essentially prevented providing nourishment and silt to the wetlands so that they basically can keep up with the water level, because the land is sinking and sea levels are rising. Without the river, you cannot--the land cannot maintain its elevation relative to the rise in water.

BLOCK: When you went up this week in a helicopter to look at these wetlands, describe what you saw.

Prof. TWILLEY: Well, let's go to Breton Sound. Breton Sound is an area that is bounded on the east and the west by a levee system. The storm energy, of course, is in a sort of a circular motion, right? It spins, as everyone sees in the satellite images, and you really can see across the landscape the translation of what you see in a satellite image to essentially a scouring in almost circular patterns that replicate the energy field of a hurricane. And so what once was a carpet of wetlands are now essentially circular scouring patterns where there's ribbons of wetlands but large areas of open water.

BLOCK: How do you take a river like the Mississippi that, to some extent--to a great extent, has been artificially channeled and straightened and diverted from where it would naturally go--how do you fix that? What specifically can you do to make a more--to make it mimic what nature would ordinarily do?

Prof. TWILLEY: Well, we have mechanisms--we had one built in 1992--that are called freshwater diversions. They basically reconnect the river to the floodplain. These are cement structures. They don't use pumps. They have gates. When the river level is at a certain height, by gravity, water flows through the gates, through a series of canals, and nourishes the wetlands.

BLOCK: Would you need more diversions like that?

Prof. TWILLEY: Correct. We have already planned four additional diversions. But those structures are not going to rebuild the deficit that we're at right now. That's a very important point. That is only one part of the formula that includes a very aggressive shoreline protection system by rebuilding our barrier islands.

BLOCK: Well, how would you rebuild those barrier islands?

Prof. TWILLEY: Well, basically we need sand and we need larger particles that are transported down the river and they flow along the coastal boundary. And we may have to again use some artificial structures to maintain the barrier islands because we may not have as much resources as we had before.

BLOCK: There have also been a lot of canals cut through the wetlands for petroleum exploration, for shipping channels. Do you just accept those as a fact of life, that there's really nothing to be done about that?

Prof. TWILLEY: No, it's a very good point. You know, the key point about this coast and the fact that it is a working coast is it requires access to specific locations, to shipping, to oil and gas rigs, to operations, and access requires canals. That access also moves water; it moves sod; it moves a lot of the other elements that are part of the risk that these communities are having to deal with. We have got to re-evaluate access.

You know, again, there's a compromise here because there's a lot of the canals that I don't think industry would mind--there would be no problem that we knock down the dredge boyles(ph) that exist, the artificial banks that prevent water from flowing out into the wetlands. You know, there are a lot of pipelines out there that were covered by wetlands, and it's very important those wetlands stay there to protect that infrastructure. And so there's a very aggressive campaign by industry to make sure that we have sustainable wetlands in this area as well.

BLOCK: Robert Twilley, thanks for talking with us.

Prof. TWILLEY: Thank you.

BLOCK: Robert Twilley is a professor in the department of oceanography and coastal science; he's also director of the Wetlands Biogeochemistry Institute at Louisiana State University.

SIEGEL: Hassan Mashriqui is a civil engineer at LSU's Hurricane Center. Using computer modeling, he and his colleagues have studied the systems that are designed to protect New Orleans from storms like Katrina. In their work, they highlighted a key point of vulnerability in the city. It lies where two canals east of downtown join into one. During Katrina, this area served as a funnel, bringing floodwaters into the city. Mashriqui says re-engineering these canals is not an easy task.

Dr. HASSAN MASHRIQUI (Hurricane Center, Louisiana State University): I mean, if you break a bone, then how do you unbreak it? I mean, generally people or engineers suggest that we put a floodgate. This floodgate means you open it when you need it to be open, and you close it when there is storm surge. And..

SIEGEL: How big is a floodgate that you're talking about?

Dr. MASHRIQUI: It is--it would be on the Gulf Intracoastal Waterway, and the exact size I don't know. It has to cover the entire water body there, so maybe we're talking about a half-mile or something.

SIEGEL: What might be a 21st-century successor to the levee and the seawall?

Dr. MASHRIQUI: Well, if you look at the New Orleans from every side, we were surprised to find out that the safest side of New Orleans is the Mississippi River side. And personally, I was surprised because I thought that generally if you have a mighty river like Mississippi flows through New Orleans, then that's where you expect to see flood. But Corps of Engineers, after 1927, were given basically a kind of mandate to do whatever it takes so that Mississippi never overfloods. So they have very strong levees which are very dependable, and I don't think--they're much more dependable and stronger than what we have in the lakefront side. And those are really levees. Even if they overtop, they don't create disaster. In what sense? If they overtop, then they still hold, and whatever water spills over is--that water gets spilled over it. So the levees as strong as Mississippi River levees would be a better choice. But obviously, I would like an national level kind of involvement from engineers of all side to look at this design and make it really, truly American standard.

SIEGEL: Of course, there's another question that comes to mind. It certainly was not what was on President Bush's mind when he said New Orleans will rise again. And that is that New Orleans is, in part for natural causes, in part for man-made reasons, an island sitting off the Gulf Coast shore of the United States. It's below sea level, mostly, and we have to build up walls to make a bowl to protect it from flooding. It's just not a great place for a city is another argument.

Dr. MASHRIQUI: Well, it's how you look at it. If your city--if you fall in love with this city, then it doesn't matter how the city looks; you still love it. And I'm from Bangladesh, and I raised my hand in New Orleans and became a US citizen. And I have a special place for this city. I just can't think of anybody describing any city other than being beautiful.

SIEGEL: OK. Well, Dr. Mashriqui, thank you very much for talking with us about the civil engineering issues involved.

Dr. MASHRIQUI: Thank you so much.

SIEGEL: That's Hassan Mashriqui, an engineer at LSU's Hurricane Center.

BLOCK: We also heard from Robert Twilley. He runs LSU's Wetlands Biogeochemistry Institute. Both were talking about the scientific challenges to rebuilding New Orleans and southeastern Louisiana.

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