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The Joys of Art

Thursday, March 23, 2006

A Little Less Talk and a Lot more action

Little Less Talk and a Lot more Action--Toby Keith

I guess they are all waiting for a booming voice from heaven to sound before Congress and others start to act on this.....What part of start restoring the wetlands doesn't their azzes understand?!! What part?!!! Not only do we have a detached President it seems as though we have a detached Congress as well!!!! Alright Congress let's get to work!!!!! How come these people get it but yet Bush and Congress can't?!!!

Restoring wetlands as important as rebuilding levees, expert says

By Bob Marshall
Staff writer

The 20 Arpent canal levee runs straight as a green arrow through the wetlands of eastern St. Bernard Parish, its sides covered with a thick carpet of grass, its crown dry and firm enough to support the SUV Hassan Mashriqui has just stepped from to begin his lecture.

With a wide wave of his arm the Louisiana State University researcher is explaining that on Aug. 29 the western edge of Hurricane Katrina’s eye wall passed over this spot, its 85 mph winds driving 5-foot waves across the top of a storm surge that would rise to 17 feet on the nearby Mississippi River-Gulf Outlet. Levees just to the north and east of where Mashriqui stands crumbled under the shock of waves and water, allowing a flood of death and destruction to swamp the parish.

But the only evidence of that violent night on the 20 Arpent Canal levee is a line of marsh grass that rests about 10 feet from its crown.

“Why the difference?” asks Mashriqui, who quickly provides the answer by pointing to the thin line of trees and marsh beyond the debris line. “It is this marsh and those trees that saved this levee.

“This is called greenbelt defense. On soils like we have, marsh and trees — even small amounts — can be better armoring than concrete and steel, because they don’t sink, and don’t have to be rebuilt.

“Katrina has proven these are things we must start considering.”

In the months since Katrina took only a few hours to humble the system of levees and floodwalls built by the Army Corps of Engineers over 40 years, most of the headlines have been generated by investigations focused on “what went wrong.” But a quieter, equally important story is being written by researchers studying what went right.

Storm specialists want to know why Katrina’s fury reduced some levee sections to warm Jell-O while others nearby stood tall and strong. The answer, they are finding, comes in two parts.
The most obvious reason, according to Texas A&M researcher Jean-Louis Briaud: Some levees were built of tougher stuff than others.

In lab tests developed by A&M, core samples from levees that withstood Katrina consist of clays that are highly impervious to water. Conversely, samples of levees that evaporated in the storm were built of highly organic materials offering little resistance to water.

But another lesson emerging from Katrina is that the presence of wetlands — wooded wetlands as well as marshes — proved to be effective natural armoring for levees. From the MR-GO to eastern New Orleans levees with a buffer of wetlands had a much higher survival rate than those that stood naked against Katrina’s assault.

“If you travel the area and look at what survived and what didn’t, it becomes obvious,” Mashriqui said. “And this is not news. Other countries have been using natural barriers to protect against storms for many years.”

The concept of wetlands as storm buffers certainly is not new to Louisiana. In the late 1960s the corps produced a report that has become gospel for coastal wetlands advocates: 2.7 miles of coastal marsh reduces storm surge by 1 foot. And while many storm researchers today consider that report to have been widely misinterpreted, there is no disagreement on the statement that wetlands can reduce the worst effects of a hurricane: wind and rising water.

The problem is that much of the wetlands that once stood between New Orleans’ levees and the Gulf of Mexico have been destroyed by manmade developments. And while environmentalists for years fought a lonely battle against wetlands abuse, Katrina provided a deadly demonstration of their importance in storm protection — not just in huge swatch many miles wide, but even in relatively narrow borders adjacent the levees, researchers like Mashriqui contend.

Marsh and wooded wetlands reduce the impact of hurricanes in different but essential ways.

Friction from marsh grass reduces the speed, or current, of the surge as it travels across an area, but not as most people would imagine. The common concept of a storm surge is a wind-driven wall of water rolling across the landscape. That isn’t the case. A storm surge is a dome of water that rises over hours and days as a hurricane nears the coast. The direction and speed the surge travels is determined by the path and speed of the storm — not the winds aloft.

For example, during Katrina northeast winds drove huge waves against the southwest shoreline of Lake Borgne and the MR-GO levees. But below the surface the surge was actually moving — flowing — in a northwest direction.

It’s a critical distinction, because moving water will eventually erode a levee the way a rushing river cuts into its banks. The faster a storm surge current brushes the surface of a levee, the more danger it is in. So reducing the speed of that surge is important.

Mashriqui said data collected by the state showed the speed of the surge in the open water of the MR-GO approached 7 feet per second as it flowed over the shoulders of the levee at the Bayou Bienvenue floodgates. But in the marshes across the channel, friction from grasses and shrubs reduced that speed to 3 feet per second.

“If you can reduce the surge speed by half, this is very important to protecting levees,” he said. “Had there been marshes in front of the MR-GO levee instead of the (2,000-foot) wide canal, they would have had a much better chance.”

In addition to being a speed bump to storm surge, large expanses of marshes also provide a de facto rise in ground elevation, Mashriqui said.

“If the top of the marsh grasses is 3 feet, then in effect you have raised the land elevation by 3 feet,” he said. “To build waves, the surge must first flood that marsh with 3 feet of water, then add water to the top of that. And the marsh grasses are so thick, if they stand 3 feet tall, the surge must be 3 feet higher to gain momentum, force and speed.

“So, far all practical purposes, you are gaining elevation for your levees and your communities with marshes.”

Wooded wetlands such as the cypress swamps that once ringed New Orleans, are even more effective at reducing the impact of storm surge, researchers said, because their height and size act as natural breakers for wind as well as water. A study done by Japanese scientists showed an area about the size of a football field (100 yards by 50 yards), with a tree density equal to what is found in most Louisiana swamps would reduce the wave energy in a storm by 90 percent, LSU researchers said.

“If you had a border of even small trees like willows, you can significantly reduce wave energy,” LSU researcher Paul Kemp said. “The waves are breaking against trees instead of against levees. That’s really important in our areas, because the levees are not armored.

“Natural systems are very effective at protecting levees and other storms defenses, and they have the added benefit of offering other environmental benefits, such as helping fisheries. ”

However, quantifying the storm-dampening effects of wetlands is tricky business, experts said. Much depends on the size of a storm as well as its forward speed.

“You’ll get a lot more benefit from wetlands during a fast-moving storm, because the surge has less time to build,” Kemp said. “But in a slow-moving storm — something that just sits over the area for days — then you’ll eventually just be overwhelmed.”

The type of wetlands in a storm’s path also are important. For example, that 1960s study by the corps was based on storms that had come ashore in southwestern Louisiana, which has many miles of healthy freshwater marshes crossed by natural ridges called cheniers that are forested with oak trees. Southeastern Louisiana’s coastal marshes are built on young river deltas, and are much thinner and more fragile, with few ridges.

“Even before the amount of erosion that has taken place in southeastern Louisiana, you probably wouldn’t see that level of surge reduction (in southeast Louisiana) as they did in that study,” said Joe Suhayda, a retired LSU professor. “So the type or quality of the wetlands is very important.

“The reduction in surge will depend on the characteristics of each storm, and the wetlands it crosses.”

But by comparing actual storm surges against predictions, LSU researchers can provide an estimate of what wetlands could have meant to metro New Orleans area during Katrina. Their sophisticated storm-surge models, while accurate for areas that are not protected by wetlands, consistently over-predicted surge heights in areas that were protected by wetlands.

For example, the surge prediction for St. Charles Parish adjacent to the Bayou Labranche wetlands were 2 feet to 3 feet higher than those actually experienced, Mashriqui said.

“You have this very large area of wetlands that have been rebuilt over the last 10 years or so that really knocked down the surge,” he said. “Also, during Hurricane Rita, our models predicted storm surge 2 to 3 feet higher for Lake Charles than they actually got. And once again, it’s a city with miles of wetlands out in front of it.”

An LSU study done on Hurricane Andrew showed that storm’s surge, estimated at between 10 feet and 12 feet when it came ashore at Pointe au Fer on the central coast, was only 8 feet when it reached Morgan City, just 25 miles inland. The only thing standing between Morgan City and the eye of the storm was the flooded forests of cypress and tupelo in Atchafalaya Basin, and its delta of freshwater marshes.

“So it’s easy to deduce that (New Orleans) could get that same kind of reduction in surge if it had the wetlands that existed many years ago,” Mashriqui said.

Re-establishing or building even narrow buffer zones of wetlands near levees could dramatically increase protection, Mashriqui said.

“If we had to look at putting dredge material down near a levee and planting it with willow trees, that is something we need to consider,” he said.

"(Hurricane planners) should start thinking outside of its box of concrete and steel. They have to do what many parts of the world are already doing with success. They must consider restoring and building natural defenses.”

Staff writer Mark Schleifstein contributed to this report.

Bob Marshall can be reached at rmarshall@timespicayune.com or (504) 826-3539.

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