Study finds rapid pre-Katrina sinking in New Orleans

[Janice]

CNN) -- Parts of New Orleans sank rapidly in the three years leading up to Hurricane Katrina, which might have made the already low-lying city even more vulnerable, a new study found.

That may explain why some levees failed during Katrina and raises serious concerns about the future of the city, according to researchers.

The study, released Wednesday by the journal Nature, found that some areas subsided 1 1/8 inch per year (28.6 millimeters) between 2002 and 2005. The average decrease was about a quarter inch (5.6 millimeters).

The area around the Mississippi River-Gulf Outlet shipping canal in St. Bernard and Orleans Parishes sunk more than three-quarters of an inch (20 millimeters) per year during that period, according to the study.

The canal's levee was one of the ones breached by Katrina's floodwaters.

"What we found is that some of the levee failure in New Orleans were places where subsidence was highest," University of Miami professor Tim Dixon said in a news release from the school. "These levees were built over 40 years ago, and in some cases, the ground had subsided a minimum of 3 feet which probably put them lower than their design level."

Scientists made the measurements by studying more than 100,000 images taken by a Canadian satellite monitoring the wetlands around New Orleans, study co-author Shimon Wdowinski said. Scientists did not know about the images until after Katrina.

"Not only is New Orleans subsiding, but the whole Mississippi delta has big problems with disappearing wetlands," Wdowinski said. "Eighty acres of wetlands a year disappear because of subsidence and sea-level rise."

He said that some places, including the Lakeview and Kenner areas, would continue to sink about an inch per year over the next 10 years but that the average would be a fraction of that.

"We need to think long term, think of what will happen in the city in 50 or 100 years," Wdowinski said. "Some areas will continue to subside, the sea level will continue to rise. Places like the Lower Ninth Ward will be 10 feet below sea level."

He said the findings raise serious concerns as officials work to rebuild the city.

"I don't think anybody wants to live in a place like that. It's just not a good idea."

An independent study into New Orleans' flood control system found serious design and construction flaws. (Full story)

The report was highly critical of the Corps of Engineers, which is in charge of the levees.

U.S. Army Corps of Engineers civil engineer Allen Coates said on Friday that the subsidence findings were surprising but would not delay plans to improve the levee system.

"I'm certain that it will have some impact. The only thing we can do at this point in time, until we survey the data, is to keep building," he said, adding that scientists and engineers would have to investigate further.

The Corps has been working to rebuild the system before the start of hurricane season, but said some parts will not be ready until later in the summer.

[Dionne]

We've been rebuilding in Waveland these past few weeks. I couldn't help but wonder how long it would be before our efforts would go under water again? We're building to these new standards that involves connectivity of the entire structure......which becomes very expensive. Irregardless of what we do......if the water comes in again like it did last Aug 29.....it really won't make much difference.

It's a haunting feeling trying to second guess mother natures plans.

[HurricaneHunter914]

You know my dad has always asked this question, " Why did they build a city BELOW sea level?". I ask the same question everyday to myself and another one," Why would people move into a city that is BELOW sea level".

[Audrey2Katrina]

You know my dad has always asked this question, " Why did they build a city BELOW sea level?". I ask the same question everyday to myself and another one," Why would people move into a city that is BELOW sea level".

At the time they "built" New Orleans, the areas settled were ABOVE sea level (along the river's natural levee banks).. it just developed from there. As to why people might do so... perhaps because they just love the city/area, millions of them live below sea-level in the Netherlands.


A2K

[timNms]

You know my dad has always asked this question, " Why did they build a city BELOW sea level?". I ask the same question everyday to myself and another one," Why would people move into a city that is BELOW sea level".

I'd venture to guess that people move to New Orleans for the same reasons people move to tornado alley or San Francisco-earthquake country, or near Mt. St. Helens, or that great hurricane magnet we all know and love called Florida I can't think of anywhere else I'd rather live than where I am now. And we all know how bad it was during Katrina. We've also had our share of tornadoes in this area. But I have no plans to move away because of those things.

No one is immune to natural disasters whether they are below, at, or above sea level.

[Yarrah]

You know my dad has always asked this question, " Why did they build a city BELOW sea level?". I ask the same question everyday to myself and another one," Why would people move into a city that is BELOW sea level".

It's probably the fact that those regions are usualy close to the sea and in a river delta. These kind of places are really good trading posts, since you have a connection with the sea and with places further up the river. These trading posts often become cities, such as New Orleans and the cities in the Netherlands.